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Heterologous interchange and non-disjunction of distributively paired chromosomes in Drosophila melanogaster: Immature oocytes
Muta;tion Research, 23 (I974) t89-196
"{?Elsevier Sc(entific Publishing Company, Amsterdam
Printed in The Netherlands
I8 9
H E T E R O L O G O U S I N T E R C H A N G E AND N O N - D I S J U N C T I O N OF D I S T R I B U T I V E L Y P A I R E D CHROMOSOMES IN DROSOPHILA MELANOGASTER: IMMATURE OOCYTES*
J O H N H. W I L L I A M S O N
Department of Biology, University of Calgary, Calgary, Alberta (Canada) (Received D e c e m b e r I9th, I973)
SUMMARY
The relationships between interchange-mediated disjunction and segregation of distributively paired chromosomes have been analyzed. Even when an interchange generates a quasi-bivalent, one component of which is either the compound-X or the Y chromosome, the uninvolved sex chromosome disjoins from its regular disjunctive partner more often than not, Interchange between distributively paired heterologs does not remove these chromosomes from the distributive pool, a consequence of which would be regular disiunction of those elements remaining in the distributive pool.
INTRODUCTION
Meiosis in the female of Drosophila melanogaster consists of a complex sequence of events and has been partially analyzed by a variety of contrived genetic and cytogenetic experiments. Cytological documentation that meiosis in females does not deviate significantly from the classical description of meiosis has only recently been published 2. The only apparent major exception is that in the oocyte the chromosomes appear to be associated by a chromocentral arrangement, a situation that may prove to be standard in some groups of organisms. From her analysis of a series of genetic experiments, GRELL has described meiosis in tile female as a sequence of events consisting of (z) exchange pairing, (~') exchange, (j') distributive pairing and (4) disjunctiona, 6. Exchange pairing may be equated with synapsis of homologous chromosomes while exchange in this species is limited to the female and is coincident with the period of DNA synthesisS,L The period during meiosis in which exchange occurs is relatively short and occurs some 6 days prior to disjunction in reproductively active females. Distributive pairing involves non-exchange chromosomes, either homologs or heterologs, and is required by GRELL'S data to occur subsequent to exchange. The precise timing of the initiation of distributive pairing has not been established; the maintenance of distributive pairing relationships normally continues until just prior to * S u p p o r t e d b y the N a t i o n a l R e s e a r c h Council of ( ' a n a d a .
I90
J.H. \VILLIAI~'ISON
disjunction, i.e. for approximately 6 days sT. This is a necessary deduction since meiosis is arrested in late prophase until fertilization, after which the meiotic divisions are completed within a few minutes a. Distributive pairing is limited to the female, this being consistent with the conclusion reached from the study of meiotic m u t a n t s that the first meiotic division is under different genetic control in the 2 sexes 22. Another approach to the analysis of meiotic events in the female of D. mda~zogaster is the recovery and genetic analysis of chromosomal rearrangements induced at particular stages of oogenesis~, l° 2~,~-~9. These analyses have necessarily concerned rearrangements involving a compound-X, the Y and the fourth chromosomes for a variety of reasons. Vor example, sex is determined by the presence of I (male) vs. 2 (female) X chromosomes, hyperploidy for all or part of the fourth and Y chromosomes has little, if any, detrimental effect on viability of either sex, and hypoploidy for the fourth and Y chromosomes can be compensated for by using appropriate parental stacks. The distributive pool of females carrying a c o m p o u n d - X chromosome is composed of the compound-X, the f(mrth chromosomes and Y chrolnosome, if present a. Irradiation of c o m p o u n d - X females frequently results in detachment of the 2 X chromosomes and usually involves the Y chromosome or a fourth chromosome. Such induced interchanges are chromatid events and effectively conjoin the 2 involved chromosomes with a cross over-like event; the resultant complex has been called a quasi-bivalent. When females lacking a Y chromosome are irradiated C(I)-.! interchange results in orientation of the centromeres of these chromosomes such that they segregate at the first meiotic division. This led to the conclusion that bivalent conjunction rather than bivalent homologyis recognized b y t h e disjunctive process ~5.When interchange conjoins the c o m p o u n d - X and a fourth chromosome, 2 ot the 3 elements of the distributive pool have been removed and effectively placed back into the exchange pool. The uninvolved fourth chrolnosome, which wouM have disjoined from its homolog because of size similarity, behaves as a univalent and segregates at random with respect to the C(z)-.~ quasi-bivalentl% ~. When similar females carrying a Y chromosome are irradiated C(I)-Y interchange occurs more frequently than does C(r)-4 interchange ~s,~",~°. In addition, Y-:I interchange occurs and can be recognized by the recovery of partial Y chromosomes showing linkage with fourth chromosome markersl'~,27, 28. These Y-4R fragments are often recovered in females and when so recovered are seldom recovered along with a free fourth chromosome. Y-4R fragments recovered in male progeny of the irradiated females are frequently recovered along with a free, homologous fourth chromosome. This has been assumed to indicate that Y-4 interchange generates a Y-4 quasi-bivalent, the centromeres of which disjoin at the subsequent first meiotic division. Thus, the results of several experiments indicate that interchange can effectivel\ remove elements from the distributive pool and direct their disjunction at anaphase I. InC(z)R;II/Y females segregational behavior of the elements remaining in the distributive pool, I member from each of 2 pairs, has not been adequately analyzed. From previous experiments it was not permissible to suppose that the 2 elements reinaining in the distributive pool would form new conjunctive relationships with each other and assort apart. This would imply very simplistic rules governing an interval within a sequence of complex events. This paper describes an a t t e m p t to determine the segregational behavior of the Y chromosome and the uninvolved fourth chromosome in an oocyte in which a
INTF, RCHANGIC A N D N O N - I ) I S J U N C T I O N
IN
D. lllC[allo~6!slcf O O ( Y T E S
I9i
C ( z ) - 4 interchange has been induced. C o n c o m i t a n t l y the segregation b e h a v i o r of the C ( z ) R M and the u n i n v o l v e d 4 in oocvtes in which a Y - 4 interchange has been induced was d e t e r m i n e d . MATIn;RIALS A N D M E T H O 1 ) S
E x p e r i m e n t a l females of the g e n o t y p e ( ' ( z ) R ] I, 3' ~'b b / t3 .~"~ y ' ; cicy ,n @ / ~ ~ spav,,l were produced b y crossing C( r) R M /O; ci ev *~females with I,~ ( z ) F M 6, y:~adm B/t~'%" 3' +; still* ''l males (C( z) R M , reversed m e t a c e n t r i c c o m p o u n d X-chromosome ; Irz ( z ) F M 6, nmltiple-inversion X - c h r o m o s o m e used as a b a l a n c e r ; O, no Y chromosome; t3.%~v', a Y chroinosonae Inarked with Bar-Stone ( Bar eye) anti y*, n o r m a l b o d y color; 3', yellow body,; ~, vermilion eve color ; bb, small bristles ; ci cubitus i n t e r r u p t u s , a wing vein m u t a n t ; t,3,n, eyeless-Russian; spavor, poliert, an eye-smface n m t a n t ; &n, small bristles). Females were collected at I2-h intervals, t r e a t e d with 2ooo R of X - r a y s at 45o R/rain and stored 24 h on fresh mediuin sprinkled with d r y live yeast. The i r r a d i a t e d females were m a t e d to 4 - d a y - o l d y ze,"y r . y,s./y; ci t'3~/¢spa* ','t males in 1/4 t)int bottles, with IO females a n d 2o males per bottle (ze" w h i t e apricot). Parental flies were discarded after 48 h. The c o m p o u n d - X Y assured the recovery of n u l l o - X oocvtes as fertile males a n d the recovery of Y-chroinosoine f r a g m e n t s since it carries all of the X a n d Y chromosomes necessary for v i a b i l i t y and fertility. The free Y chromosome assured t h a t d e t a c h m e n t males carried a full set of male fertility loci. All exceptional p r o g e n y were tested by, backcrossing females to y ~e,"y L . y s / y ; ci ev ~¢ s/YaV~,l males and e x c e p t i o n a l males to C ( z ) R M , 3' "('t~t)/Y; cio,~spa*'"l females. These p r o g e n y tests allowed confirmation of X - Y linkage, X - 4 R linkage, Y - 4 R linkage the presence of free fourth chromosomes and their associated markers, and the presence of u n a l t e r e d Y chromosomes. In some instances p r o g e n y of d e t a c h m e n t - b e a r i n g females had to 1)e backcrossed a second time to positively d e m o n s t r a t e linkage of the X - c h r o m o some m a r k e r s with m a r k e r s from e i t h e i the Y or the fourth chromosomes. All crosses were m a d e on cornmeal-dried brewer's yeast sucrose dextrose agar m e d i u m with t)ropionic acid as a mold inhibitor and i n c u b a t e d at -o5~ and 4oC~, relative h u m i d i t y . All progeny tests were m a d e in 8-dram vials. A complete description of the listed m u t a n t s and special cl~romosomes can be found in LINI)SLEV AND GREI.I. ~. I{ESULTS
The results of this e x p e r i m e n t are s u m m a r i z e d in Table I. F r o m a t o t a l of 31 3_°7 p r o g e n y I7I 4 were scored p h e n o t y p i c a l l y as exceptiorLs a n d were p r o g e n y tested individually. Of these, I537 were completely analyzed. Each was scored as to the X, Y a n d fourth chromosome m a r k e r s carried and the linkage relationships of these markers. The various r e a r r a n g e m e n t and aneuploid classes are g r o u p e d in Table i. D e t a c h m e n t s of the c o m p o u n d - X chronlosome involved t h e Y-chromosome in 286 cases of a total of 4oo d e t a c h m e n t s analyzed. Linkage of fourth chromoson~e m a r k e r s with X chromosome m a r k e r s occurred 68 times and in the remaining 46 cases the interchange p a r t n e r of the C ( z ) R M could not be identifi.ed. In almost every case of C ( z ) - Y interchange (28o/286) the o fourth chromosomes had disjoined regularly,. In the 6 e x c e p t i o n a l cases the C ( z ) Y d e t a c h m e n t was recovered from diplo- 4 oocvtes. The 6 were recovered equally, in male and female p r o g e n y and contained homologous
192
J . H . WILLIAMSON
TABLE
I
SUMMARY OF P R O G E N Y OF I R R A D I A T E D C(%)Rl~,1, y v bb / B S y y + ; ci ey It / spaP °z FEMALES MATED TO ATTACHED X Y / }z; ei ey R spaP °~ MALES
Regular progeny Exceptions: Total Fertile Completely analyzed Detachment class
Females
X-4R / 0 X - 4 Ra / 4 b*
13
6
20
19
X-4R / BSyy + X-4Ra / 4h / BSyy + X-?
22
X- ? / 4 / BSyy + X-Y / 4 X - Y / 4a / 4b Non-disiunction C(z)RM / 4 /Bs~v ~ C ( I ) R M / .t a / 4 b Nullo-X Nullo-X
/ 4 / 4 a / 4 t~
14 6 4 7 490 433 433
~4 i I i
966 224 lO6 lO 4
Y Fragments
Females
Males
Y-4 R / 0 Y-4 Ra / 4 b Y-4 Ra / 4 a
23 8
19 56
I
o
Y-? /4 Y - ? / 4a / 4 b
4
I43
o
o
i
o
22
2
o
I83
97
3
3
50 97 o o
o o 487 248
* 4 a and 4 b are homologs,
Males
Males
6 o
/4
Females
Recombinant-
4
not sisters.
fourth chromosomes, not sisters. 39 of the X - 4 R d e t a c h m e n t s were recovered with an a d d i t i o n a l free fourth chromosome t h a t was the homolog of the fourth chromosome involved in the interchange. In IO cases the X - 4 R d e t a c h m e n t was recovered w i t h o u t a free fourth chromosome b u t with an u n a l t e r e d Y chromosome. In 19 cases the X - 4 R d e t a c h m e n t was recovered with neither a free fourth nor a Y chromosome. In no case was an X - 4 R d e t a c h m e n t recovered with a free t o u r t h a n d an i n t a c t Y chromosome. I n t e r c h a n g e involving the Y chromosome b u t not t h e C ( z ) R M g e n e r a t e d Y - 4 R fragments recovered w i t h o u t a free fourth chromosome equally f r e q u e n t l y in the 2 sexes (23 in females :19 in males). Of those Y-4 R f r a g m e n t s recovered with a free fourth chromosome 64 of 65 were recovered with the homolog; in only one case in the entire e x p e r i m e n t was the sister of the interchange-conjoined fourth chromosome recovered at the same time as the involved chromatid. Of the 64 recoveries of a Y - 4 R f r a g m e n t and a free homolog 56 were recovered in males. Diplo- 4 oocytes are a consequence of i r r a d i a t i n g i m m a t u r e oocytes a n d have been d e m o n s t r a t e d to be one of the consequences of d i r e c t e d disjunction of interchange-conjoined quasi-bivalents 21, 53-20. Such i n t e r c h a n g e - m e d i a t e d n o n d i s j u n c t i o n is recognized b y the recovery of diplo-4 oocytes as male exceptions much more often t h a n as female exceptions. N u l l o - X oocytes were recovered 735 times in males; of these 248 were s i m u l t a n e o u s l y diplo- 4. DISCUSSION
A v a r i e t y of e x p e r i m e n t s has d e m o n s t r a t e d t h a t r a d i a t i o n - i n d u c e d interchange in i m m a t u r e oocytes directs the disjunction of the centromeres of the quasi-bivalent
I N T E R C H A N G E A N D N O N - I ) I S J U N C T I O N IN
D. lllclaJlogastgt"
OOCYTES
193
to opposite poles at the first meiotic division. In females without a Y chromosome interchange often involves the C(z)RM and a fourth chromosome. As a consequence the uninvolved fourth chromosome apparently behaves as a univalent and segregates at r a n d o m with respect to its normal pairing partner. One of the observed results of this altered segregation behavior is dose-dependent, interchange-mediated non-disjunction of the fourth chromosomes. These nullo-X, dilpo- 4 oocytes are recovered as one of the classes ot exceptional male progeny. When a Y chromosome is carried by the irradiated C(I)R3I females a high frequency of C(z)-5" interchange is observed along with a concomitant decrease in the frequency of C(z)-4 interchange. In addition, Y-4 interchange frequently (~ccurs and is recognized by the recovery of Y chromosome fragments showing linkage of Y and fourth chromosome markers. When the resultant Y-qR fragment is recovered in females it is usually recovered without a free fourth chromosome, implying t h a t the homologous fourth chromosome segregated to the opposite pole as did the C(z)RM and Y-4R fragment. One of the consequences of such segregations is the induction of nullo-X, haplo- 4 oocytes which are recovered as exceptional male progeny. In the present data these comprise the largest class of exceptional progeny (487). Irradiation of mature oocytes results in completely different disjunctional events as has been adequately demonstrated~,2s, 29. In C(z)RM/Y females the distributive pool is composed of the compt~und-X, the Y and the 2 fourth chromosomes. The c o m p o u n d - X anti the Y disjoin regularly; the fourth chromosomes are significantly smaller and also disjoin regularly. Disjunction of the pair of fourth chromosomes is at r a n d o m with respect to disjunction of the C(~)RM and Y chromosomes. An interchange between the C(z)R3I and one of the fourth chromosomes effectively removes one member of each pair of distributively paired chromosomes from the pool and directs the disjunction of the interchangeconjoined elements. A comparable situation ensues when the Y and one of the fourth chromosomes are interchange-conjoined. The behavior ol the Y and the uninvolved fourth chromosome in the first case and C(z)RM and the uninvolved fourth chromosome in the second case has not been previously analyzed. One prediction is that the uninw~lved chromosomes making up the modified distributive pool will re-associate and will disjoin from each other in a regular fashion and independently of the interchange quasi-bivalent. For example, in an oocvte with an induced C(])-4 interchange the Y chromosome and the uninw~lved fourth chromosome m a y form a "new distributive relationship" and disjoin from each other at first division. Since in the unincumbered situation the heteromorphic pair of sex chronmsomes and the pair of fourth chromosomes segregate at r a n d o m with respect to each other, the above prediction might be extended to expect that the "reconstituted" pair (Y and 4) would segregate at random with respect to the interchange-conjoined quasi bivalent. The predictions in Figs. i and 2 are based on the assumption t h a t removal of one member of each pair of distributively paired chromosc,mes allows a "re-association" of the remaining 2 chromosomes and that these 2 disjoin at r a n d o m with respect to the quasi-bivalent. The prediction from Fig. I is that an X-4R detachment will be recovered with a Y chronmsome and no free fourth chromosome as often as an X-4R detachment is recovered with a free (homologous) fourth chromosome and no Y chromosome (Fig. z ; Alb vs. Bxb). The data in Table I are convincing that this prediction doesn't hold. X-4R detachments recovered with a Y chromosome but no free fourth chromosome are
z94
j . H . WILL1AMSON DIVISION
I
DIVISION
Tr
f A~
~
==2m
a
0
b
I
B~
GAMETES
{
a-->o
~
--o-
0
v~
Fig. 1. Hypothetical segregation of chromosomes when an interchange conjoins the C(z)RM and a fourth chromosome and if the Y chromosome and the uninvolved fourth chromosome segregate from each other and independently of their regular disjunctive partners. Thin lines represent the C(z)R31, wavy lines represent the Y chromosome and thick lines represent the fourth chromosonles.
r e p r e s e n t e d z() t i m e s w h e r e a s X-4R d e t a c h i n e n t s r e c o v e r e d w i t h a free f o u r t h c h r o m o s o m e a n d n o Y a r e r e p r e s e n t e d 39 t i m e s . I n a d d i t i o n , X-4R d e t a c h m e n t s I e c o v e r e d w i t h n e i t h e r a Y n o r a free f o u r t h c h r o m o s o m e are r e p r e s e n t e d z 9 t i m e s , a n d in n o ease w a s a n X-4R d e t a c h m e n t r e c o v e r e d w i t h b o t h a free f o u r t h a n d a Y c h r o m o s o m e . Fig. 2 p r e d i c t s t h a t Y-4 i n t e r c h a n g e a n d s e g r e g a t i o n of t h e C(±)RM f r o m t h e u n i n v o l v e d f o u r t h c h r o m o s o m e w o u l d r e s u l t in r e c o v e r y of Y-4R f r a g m e n t s w i t h o u t a free f o u r t h c h r o m o s o m e as o f t e n as it w o u l d r e s u l t in r e c o v e r y of Y-4R f r a g m e n t s w i t h a free ( h o m o l o g o u s } f o u r t h c h r o m o s o m e . T h e f o r m e r w o u l d b e r e c o v e r e d in f e m a l e s a n d t h e l a t t e r w o u l d b e r e c o v e r e d in m a l e s (Fig. 2 ; A~b vs. B~b). A g a i n t h e d a t a in T a b l e I d o n o t s u p p o r t so s i m p l i s t i c a n i n t e r p r e t a t i o n of t h e c o n s e q u e n c e s of i n t e r c h a n g e s in i m m a t u r e o o c y t e s . T h e r e w e r e less t h a n h a l f as m a n y Y-4R/O f e m a l e s (23) as Y-4R/4 m a l e s (56) a m o n g t h e e x c e p t i o n a l p r o g e n y of i r r a d i a t e d f e m a l e s . I n a d d i DIVISION
'T
DIVISION
Tr
t
GAMETES a
b-
A2
A
f ~ B1
B
B2
t
f
a
*
~
b
2--
a
1
b
~'
~'
b
>
~2>
a
D
0
2>
___/~o
0
Iqg. 2. Hypothetical segregation of chromosomes when an interchange conjoins the Y and a fourth chromosome, assuming t h a t the C(z)RllI and the uninvolved fourth chromosome segregate from each other and independently of their regular disjunctive partners. Thin lines represent the C(z)R31, wavy lines represent the Y chromosome and thick lines represent the fourth chromosomes.
INTERCHAN(~E AN1) NON DISJUNCTION IN D. inclauo~asler OOCYTES
105
tion, t h e r e were a b o u t as m a n v Y - 4 R / O m a l e s as t h e r e w e r e Y - 4 R / O females 119:23). T h o s e Y c h r o m o s o m e f r a g m e n t s for w h i c h t h e i n t e r c h a n g e p a r t n e r c a n n o t be d e t e r m i n e d ( Y . ?) were r e c o v e r e d a l m o s t e x c l u s i v e l y in m a l e s as was e x p e c t e d a n d were r e c o v e r e d w i t h o n l y one m a t e r n a l f o u r t h c h r o m o s o m e in e v e r y case. T h e d a t a in T a b l e 1 are q u i t e e x t e n s i v e c o m p a r e d w i t h t h o s e from p r e v i o u s e x p e r i m e n t s . F o r t h e m o s t p a r t t h e y v e r i f v t h e m a j o r details of t h e n a t u r e of t h e r e c o v e r y of r e c o m b i n a n t c h r o m o s o m e s f r o m i r r a d i a t e d females, yet s o m e differences are a p p a r e n t . D e t a c h m e n t s of t h e C ( I ) R M are u s u a l l y r e c o v e r e d e q u a l l y f r e q u e n t in t h e 2 sexes a n d this is t r u e in m o s t classes of d e t a c h m e n t s s m n m a r i z e d in T a b l e I. T h e X - } ' / 4 class, h o w e v e r , has a r e c o v e r y r a t i o ol I83 f e m a l e s to 97 males. A recessive l e t h a l carried b v t h e C ( r ) R M w o u l d e x p l a i n this d i s c r e p a n c y e x c e p t for t h e fact t h a t t h e o t h e r classes o{ d e t a c h m e n t s w o u l d be e x p e c t e d to d e m o n s t r a t e an m l e q u a l sex r a t i o a n d t h e y do not. T h e r e is no a p p a r e n t e x p l a n a t i o n for t h e u n e q u a l sex r a t i o in t h e X - Y class of d e t a c h m e n t s . A n o t h e r m i n o r d i s a g r e e m e n t of t h e d a t a in T a b l e I a n d p r e v i o u s d a t a is f o u n d in t h e sex r a t i o of Y-4 R recoveries. PARKER'S 1:1,15,16 d a t a in e l u d e d a s m a l l excess of m a l e s in t h e s e classes of e x c e p t i o n a l p r o g e n y while in T a b l e I t h e y are in a r a t i o of 32 females to 75 males. T h e s e d i s c r e p a n c i e s are n o t of i m p o r t a n c e h o w e v e r , in t h a t t h e y do n o t b e a r on t h e m a j o r q u e s t i o n s asked in this e x p e r i n l e n t . I t is o b v i o u s f r o m t h e s e c o n s i d e r a t i o n s t h a t i n t e r c h a n g e i n v o l v i n g tile C ( I ) R z l I and a fourth cllromosome and interchange involving the Y chronlosome and a fourth c h r o m o s o m e does n o t p r e c l u d e s e g r e g a t i o n of t h e C ( I ) R M a n d t h e Y c h r o m o s o m e s . I n d e e d , it a p p e a r s t h a t e v e n w h e n an i n t e r c h a n g e i n v o l v e s one b u t n o t t h e o t h e r of this pair of h e t e r o m o r p h s , t h e y t e n d to s e g r e g a t e from e a c h o t h e r m o r e 1ift e n t h a n not. In o t h e r words, d i s t r i t m t i v e p a i r i n g r e l a t i o n s h i p s of t h e C ( I ) t , LII a n d t h e Y c h r o m o sonles t e n d to be c o n s e r v e d e v e n w h e n C ( I ) - 4 a n d }'-4 i n t e r c h a n g e s are i n d u c e d . W h e t h e r or n o t t h e s e d a t a are i n d i c a t i v e of p r e - e x i s t i n g r e l a t i o n s h i p s b e t w e e n all of t h e m a n i t m l a t e d c h r o m o s o m e s is n o t clear. A e h r o m o c e n t r a l - l i k e r e l a t i o n s h i p of chron l o s o m e s in tile o o c y t e n u c l e u s has b e e n p r o p o s e d as one of the l e a s o n s t h a t t h e h e t e r o c h r o m a t i c regions of all of t h e c h r o n l o s o n l e s in t h e D r o s o p h i l a g e n o l n e call be i n v o l v e d in interchange12, 2v,'-'~, a n d r e c e n t l y a c h r o m o c e n t e r in t h e o n c v t e has been d e m o n s t r a t e d 2. A n y r e l a t i o n s h i p b e t w e e n an o v a r i a n c h r o m o c e n t e r a n d d i s t r i b u t i v e p a i r i n g r e l a t i l m s h i p s in i r r a d i a t e d females r e n l a i n s to be d e t e r m i n e d .
R 1':1:1':R KN(' I';S i V,ust~v, N., Segregation following interchall~e incluced by irradiating mature oocytes of Drosophila melanogaster, 3latation I¢,:s., 11 11971 ) 391 306. 2 I)AVRING, L., AND ~i. SI.'NNER, Fenlale meil)sis and enlbryonic mitosis in Drosophila melanogash'r, I. Meiosis and fertilization, Hereditas, 73 11973) 51 64. 3 (;nELL, E. H., Distributive pairi.ng lff compound chromosomes in females of Drosophila mclam~gaster, Gem,tics, 48 (19631 1217 I22% 4 (]RELL, R. 1:., A new model for secondary non disjunction: the role' of distributixc pairing, Genetics, 47 (1962) 1737-~754. 5 (;RI~LL, R. I:., The naeiotic origin of t~'mpcrature-induce(1 crossovers in Drosophila mHanogaster females, (;era'tics, 54 (10061 4 It 421. 0 (;RELI., R. F., Pairing at the chromosomal level..]. Cell Physiol., 7o, .Suppl. l (I9()~) 119 I40. 7 (;R~=LL, R. F., leeconlbination and I)NA replication in the Drosophila melanogaster oocyte, Gem'tics, 73 (~973) ~7 io8. S |',[IN(;, R. C., A. C. Ru~tNS/lX AXl) R. 1:. SMITH, ()o~4cnesis in adult Drosophila melanogasler, (;r,~wth, 2o (i056) I2I ~57.
196
J.H.
WILLIAMSON
9 LINDSLEY, i). L., AND ]?.. H. GRELL, Genetic v a r i a t i o n s of Drosophila melanogaster, Carnegie Inst. Wash. Publ., 627 (19681. 10 PARKER, D. R., R a d i a t i o n - i n d u c e d e x c h a n g e s in Drosophila females, Proc. Natl. dcad..';ci. (U.S.), 40 (19541 795-800. 1 I PARKER, D. R., On t h e n a t u r e of s e n s i t i v i t y c h a n g e s in oocytes of Drosophila melanogaster, in F. H. SOBELS (Ed.), Repair from Genetic Radiation Damage, P e r g a m o n , Oxford, 1963, pp. 11-19.
12 PARKER, l). R., Chronaosoine pairing a n d i n d u c e d e x c h a n g e in Drosophila, Mutation Res., 2 (1965) 523-529. 13 PARKER, D. R., I n d u c e d heterologous e x c h a n g e at nieiosis in Drosophila, I. E x c h a n g e s b e t w e e n Y a n d f o u r t h c h r o m o s o m e s , Mutation Res., 4 (1967) 333-33714 PARKER, D. R., A s u r v e y of m e t h o d s for t h e i n d u c t i o n of a b e r r a t i o n s in meiotic stages in Drosophila females a n d for o b s e r v a t i o n s of their d i s j u n c t i o n a l properties in t h e e n s u i n g meiotic divisions, in Effects of Radiation on Meiotic Systems, I n t e r n a t i o n a l A t o m i c E n e r g y Agency, Vienna, 1968, pp. 2o9 218. 15 PARKER, D. R., H e t e r o l o g o u s i n t e r c h a n g e at meiosis in Drosophila, II. Some d i s j u n c t i o n a l cons e q u e n c e s of interchange, Mutation Res., 7 (19691 393 4o7 • I6 PARKER, D. R., C o o r d i n a t e d n o n d i s j u n c t i o n of Y a n d f o u r t h c h r o m o s o m e s in irradiated coinp o u n d - X female Drosophila, Mutation Res., 9 (I97 o) 3o7-322. 17 PARKER, D. R., A,XD N. BUSBY, C h r o m o s o n l a l i n t e r c h a n g e in m a t u r e oocytes of Drosophila, Mutation Res., 16 (19721 49 58. 18 PARKER, D. R., AND N. BUSBY, O b s e r v a t i o n s c o n c e r n i n g t h e effects of r a d i a t i o n s on t h e segreg a t i o n of chronlosomes, Mutation Res., 18 (19731 33-46. 19 PARKER, D. R., AND A. E. HAM~IOND, T h e p r o d u c t i o n of t r a n s l o c a t i o n s in Drosophila oocytes, Genetics, 43 (I958) 9 2 - I ° ° . 2o PARKER, D. R., AND J. McCRONE, A genetic analysis of sonic r e a r r a n g e m e n e s i n d u c e d in oocytes of Drosophila, Genetics, 43 (19581 172-186. 2I PARKER, i). R., AND J. H. WILLIAMSON, Heterologous i n t e r c h a n g e at meiosis in Drosophila, III. I n t e r c h a n g e - m e d i a t e d n o n - d i s j u n c t i o n , Mutation Res., 9 (I97 o) 273-286. 22 SANDLER, L., D. L. LINDSLEY, B. NICOLETTI AXD G. TRIPPA, M u t a n t s affecting meiosis in nat u r a l p o p u l a t i o n s of Drosophila melanogaster, Genetics, 6o (1968) 325-528. 23 TRAUT, H., E x p e r i m e n t s on t h e m e c h a n i s m s of X - r a y induced c h r o m o s o n l e loss, Mutation Res., 6 (1968) lO9-115. 24 TRAUT, H., N o n d i s j u n c t i o n induced by X - r a y s in oocytes of Drosophila melanogaster, Mutation Res., IO (197 o) I 2 5 - I 3 2 . 25 TRAUT, H., AND W. SCHEnl, Cytological analysis of partial a n d total X - c h r o m o s o m e loss induced b y X - r a y s in oocytes of Drosophila melanogaster, Mutation Res., io (197 o) 583 589. 26 TRAUT, H., AND W. SCHEID, T h e p r o d u c t i o n of m o n o s o m i c - t r i s o m i c i n d i v i d u a l s in Drosophila melanogaster b y X - i r r a d i a t i o n of i m m a t u r e oocytes, 216rutation Res., 13 (1971) 429-432. 27 WILLIAMSOX, J. H., On t h e n a t u r e of Y c h r o m o s o m e f r a g m e n t s i n d u c e d in Drosophila rnelanogaster females, I. I m m a t u r e oocytes, Mutation Res., 8 (1969) 327-335. 28 WILLIA.~:SO.N, J. H., On t h e n a t u r e of Y c h r o m o s o m e f r a g m e n t s induced in Drosophila melanogaster females, II. M a t u r e oocytes, Mutation Res., 9 (197 o) 85-9o. 29 \VILLIAMSO~', J. H., Heterologous i n t e r c h a n g e a n d n o n d i s j u n c t i o n of d i s t r i b u t i v e l y paired c h r o m o s o m e s in Drosophila melanogaster. M a t u r e oocytes, Mutation Res., 18 (19731 273-277.
"{?Elsevier Sc(entific Publishing Company, Amsterdam
Printed in The Netherlands
I8 9
H E T E R O L O G O U S I N T E R C H A N G E AND N O N - D I S J U N C T I O N OF D I S T R I B U T I V E L Y P A I R E D CHROMOSOMES IN DROSOPHILA MELANOGASTER: IMMATURE OOCYTES*
J O H N H. W I L L I A M S O N
Department of Biology, University of Calgary, Calgary, Alberta (Canada) (Received D e c e m b e r I9th, I973)
SUMMARY
The relationships between interchange-mediated disjunction and segregation of distributively paired chromosomes have been analyzed. Even when an interchange generates a quasi-bivalent, one component of which is either the compound-X or the Y chromosome, the uninvolved sex chromosome disjoins from its regular disjunctive partner more often than not, Interchange between distributively paired heterologs does not remove these chromosomes from the distributive pool, a consequence of which would be regular disiunction of those elements remaining in the distributive pool.
INTRODUCTION
Meiosis in the female of Drosophila melanogaster consists of a complex sequence of events and has been partially analyzed by a variety of contrived genetic and cytogenetic experiments. Cytological documentation that meiosis in females does not deviate significantly from the classical description of meiosis has only recently been published 2. The only apparent major exception is that in the oocyte the chromosomes appear to be associated by a chromocentral arrangement, a situation that may prove to be standard in some groups of organisms. From her analysis of a series of genetic experiments, GRELL has described meiosis in tile female as a sequence of events consisting of (z) exchange pairing, (~') exchange, (j') distributive pairing and (4) disjunctiona, 6. Exchange pairing may be equated with synapsis of homologous chromosomes while exchange in this species is limited to the female and is coincident with the period of DNA synthesisS,L The period during meiosis in which exchange occurs is relatively short and occurs some 6 days prior to disjunction in reproductively active females. Distributive pairing involves non-exchange chromosomes, either homologs or heterologs, and is required by GRELL'S data to occur subsequent to exchange. The precise timing of the initiation of distributive pairing has not been established; the maintenance of distributive pairing relationships normally continues until just prior to * S u p p o r t e d b y the N a t i o n a l R e s e a r c h Council of ( ' a n a d a .
I90
J.H. \VILLIAI~'ISON
disjunction, i.e. for approximately 6 days sT. This is a necessary deduction since meiosis is arrested in late prophase until fertilization, after which the meiotic divisions are completed within a few minutes a. Distributive pairing is limited to the female, this being consistent with the conclusion reached from the study of meiotic m u t a n t s that the first meiotic division is under different genetic control in the 2 sexes 22. Another approach to the analysis of meiotic events in the female of D. mda~zogaster is the recovery and genetic analysis of chromosomal rearrangements induced at particular stages of oogenesis~, l° 2~,~-~9. These analyses have necessarily concerned rearrangements involving a compound-X, the Y and the fourth chromosomes for a variety of reasons. Vor example, sex is determined by the presence of I (male) vs. 2 (female) X chromosomes, hyperploidy for all or part of the fourth and Y chromosomes has little, if any, detrimental effect on viability of either sex, and hypoploidy for the fourth and Y chromosomes can be compensated for by using appropriate parental stacks. The distributive pool of females carrying a c o m p o u n d - X chromosome is composed of the compound-X, the f(mrth chromosomes and Y chrolnosome, if present a. Irradiation of c o m p o u n d - X females frequently results in detachment of the 2 X chromosomes and usually involves the Y chromosome or a fourth chromosome. Such induced interchanges are chromatid events and effectively conjoin the 2 involved chromosomes with a cross over-like event; the resultant complex has been called a quasi-bivalent. When females lacking a Y chromosome are irradiated C(I)-.! interchange results in orientation of the centromeres of these chromosomes such that they segregate at the first meiotic division. This led to the conclusion that bivalent conjunction rather than bivalent homologyis recognized b y t h e disjunctive process ~5.When interchange conjoins the c o m p o u n d - X and a fourth chromosome, 2 ot the 3 elements of the distributive pool have been removed and effectively placed back into the exchange pool. The uninvolved fourth chrolnosome, which wouM have disjoined from its homolog because of size similarity, behaves as a univalent and segregates at random with respect to the C(z)-.~ quasi-bivalentl% ~. When similar females carrying a Y chromosome are irradiated C(I)-Y interchange occurs more frequently than does C(r)-4 interchange ~s,~",~°. In addition, Y-:I interchange occurs and can be recognized by the recovery of partial Y chromosomes showing linkage with fourth chromosome markersl'~,27, 28. These Y-4R fragments are often recovered in females and when so recovered are seldom recovered along with a free fourth chromosome. Y-4R fragments recovered in male progeny of the irradiated females are frequently recovered along with a free, homologous fourth chromosome. This has been assumed to indicate that Y-4 interchange generates a Y-4 quasi-bivalent, the centromeres of which disjoin at the subsequent first meiotic division. Thus, the results of several experiments indicate that interchange can effectivel\ remove elements from the distributive pool and direct their disjunction at anaphase I. InC(z)R;II/Y females segregational behavior of the elements remaining in the distributive pool, I member from each of 2 pairs, has not been adequately analyzed. From previous experiments it was not permissible to suppose that the 2 elements reinaining in the distributive pool would form new conjunctive relationships with each other and assort apart. This would imply very simplistic rules governing an interval within a sequence of complex events. This paper describes an a t t e m p t to determine the segregational behavior of the Y chromosome and the uninvolved fourth chromosome in an oocyte in which a
INTF, RCHANGIC A N D N O N - I ) I S J U N C T I O N
IN
D. lllC[allo~6!slcf O O ( Y T E S
I9i
C ( z ) - 4 interchange has been induced. C o n c o m i t a n t l y the segregation b e h a v i o r of the C ( z ) R M and the u n i n v o l v e d 4 in oocvtes in which a Y - 4 interchange has been induced was d e t e r m i n e d . MATIn;RIALS A N D M E T H O 1 ) S
E x p e r i m e n t a l females of the g e n o t y p e ( ' ( z ) R ] I, 3' ~'b b / t3 .~"~ y ' ; cicy ,n @ / ~ ~ spav,,l were produced b y crossing C( r) R M /O; ci ev *~females with I,~ ( z ) F M 6, y:~adm B/t~'%" 3' +; still* ''l males (C( z) R M , reversed m e t a c e n t r i c c o m p o u n d X-chromosome ; Irz ( z ) F M 6, nmltiple-inversion X - c h r o m o s o m e used as a b a l a n c e r ; O, no Y chromosome; t3.%~v', a Y chroinosonae Inarked with Bar-Stone ( Bar eye) anti y*, n o r m a l b o d y color; 3', yellow body,; ~, vermilion eve color ; bb, small bristles ; ci cubitus i n t e r r u p t u s , a wing vein m u t a n t ; t,3,n, eyeless-Russian; spavor, poliert, an eye-smface n m t a n t ; &n, small bristles). Females were collected at I2-h intervals, t r e a t e d with 2ooo R of X - r a y s at 45o R/rain and stored 24 h on fresh mediuin sprinkled with d r y live yeast. The i r r a d i a t e d females were m a t e d to 4 - d a y - o l d y ze,"y r . y,s./y; ci t'3~/¢spa* ','t males in 1/4 t)int bottles, with IO females a n d 2o males per bottle (ze" w h i t e apricot). Parental flies were discarded after 48 h. The c o m p o u n d - X Y assured the recovery of n u l l o - X oocvtes as fertile males a n d the recovery of Y-chroinosoine f r a g m e n t s since it carries all of the X a n d Y chromosomes necessary for v i a b i l i t y and fertility. The free Y chromosome assured t h a t d e t a c h m e n t males carried a full set of male fertility loci. All exceptional p r o g e n y were tested by, backcrossing females to y ~e,"y L . y s / y ; ci ev ~¢ s/YaV~,l males and e x c e p t i o n a l males to C ( z ) R M , 3' "('t~t)/Y; cio,~spa*'"l females. These p r o g e n y tests allowed confirmation of X - Y linkage, X - 4 R linkage, Y - 4 R linkage the presence of free fourth chromosomes and their associated markers, and the presence of u n a l t e r e d Y chromosomes. In some instances p r o g e n y of d e t a c h m e n t - b e a r i n g females had to 1)e backcrossed a second time to positively d e m o n s t r a t e linkage of the X - c h r o m o some m a r k e r s with m a r k e r s from e i t h e i the Y or the fourth chromosomes. All crosses were m a d e on cornmeal-dried brewer's yeast sucrose dextrose agar m e d i u m with t)ropionic acid as a mold inhibitor and i n c u b a t e d at -o5~ and 4oC~, relative h u m i d i t y . All progeny tests were m a d e in 8-dram vials. A complete description of the listed m u t a n t s and special cl~romosomes can be found in LINI)SLEV AND GREI.I. ~. I{ESULTS
The results of this e x p e r i m e n t are s u m m a r i z e d in Table I. F r o m a t o t a l of 31 3_°7 p r o g e n y I7I 4 were scored p h e n o t y p i c a l l y as exceptiorLs a n d were p r o g e n y tested individually. Of these, I537 were completely analyzed. Each was scored as to the X, Y a n d fourth chromosome m a r k e r s carried and the linkage relationships of these markers. The various r e a r r a n g e m e n t and aneuploid classes are g r o u p e d in Table i. D e t a c h m e n t s of the c o m p o u n d - X chronlosome involved t h e Y-chromosome in 286 cases of a total of 4oo d e t a c h m e n t s analyzed. Linkage of fourth chromoson~e m a r k e r s with X chromosome m a r k e r s occurred 68 times and in the remaining 46 cases the interchange p a r t n e r of the C ( z ) R M could not be identifi.ed. In almost every case of C ( z ) - Y interchange (28o/286) the o fourth chromosomes had disjoined regularly,. In the 6 e x c e p t i o n a l cases the C ( z ) Y d e t a c h m e n t was recovered from diplo- 4 oocvtes. The 6 were recovered equally, in male and female p r o g e n y and contained homologous
192
J . H . WILLIAMSON
TABLE
I
SUMMARY OF P R O G E N Y OF I R R A D I A T E D C(%)Rl~,1, y v bb / B S y y + ; ci ey It / spaP °z FEMALES MATED TO ATTACHED X Y / }z; ei ey R spaP °~ MALES
Regular progeny Exceptions: Total Fertile Completely analyzed Detachment class
Females
X-4R / 0 X - 4 Ra / 4 b*
13
6
20
19
X-4R / BSyy + X-4Ra / 4h / BSyy + X-?
22
X- ? / 4 / BSyy + X-Y / 4 X - Y / 4a / 4b Non-disiunction C(z)RM / 4 /Bs~v ~ C ( I ) R M / .t a / 4 b Nullo-X Nullo-X
/ 4 / 4 a / 4 t~
14 6 4 7 490 433 433
~4 i I i
966 224 lO6 lO 4
Y Fragments
Females
Males
Y-4 R / 0 Y-4 Ra / 4 b Y-4 Ra / 4 a
23 8
19 56
I
o
Y-? /4 Y - ? / 4a / 4 b
4
I43
o
o
i
o
22
2
o
I83
97
3
3
50 97 o o
o o 487 248
* 4 a and 4 b are homologs,
Males
Males
6 o
/4
Females
Recombinant-
4
not sisters.
fourth chromosomes, not sisters. 39 of the X - 4 R d e t a c h m e n t s were recovered with an a d d i t i o n a l free fourth chromosome t h a t was the homolog of the fourth chromosome involved in the interchange. In IO cases the X - 4 R d e t a c h m e n t was recovered w i t h o u t a free fourth chromosome b u t with an u n a l t e r e d Y chromosome. In 19 cases the X - 4 R d e t a c h m e n t was recovered with neither a free fourth nor a Y chromosome. In no case was an X - 4 R d e t a c h m e n t recovered with a free t o u r t h a n d an i n t a c t Y chromosome. I n t e r c h a n g e involving the Y chromosome b u t not t h e C ( z ) R M g e n e r a t e d Y - 4 R fragments recovered w i t h o u t a free fourth chromosome equally f r e q u e n t l y in the 2 sexes (23 in females :19 in males). Of those Y-4 R f r a g m e n t s recovered with a free fourth chromosome 64 of 65 were recovered with the homolog; in only one case in the entire e x p e r i m e n t was the sister of the interchange-conjoined fourth chromosome recovered at the same time as the involved chromatid. Of the 64 recoveries of a Y - 4 R f r a g m e n t and a free homolog 56 were recovered in males. Diplo- 4 oocytes are a consequence of i r r a d i a t i n g i m m a t u r e oocytes a n d have been d e m o n s t r a t e d to be one of the consequences of d i r e c t e d disjunction of interchange-conjoined quasi-bivalents 21, 53-20. Such i n t e r c h a n g e - m e d i a t e d n o n d i s j u n c t i o n is recognized b y the recovery of diplo-4 oocytes as male exceptions much more often t h a n as female exceptions. N u l l o - X oocytes were recovered 735 times in males; of these 248 were s i m u l t a n e o u s l y diplo- 4. DISCUSSION
A v a r i e t y of e x p e r i m e n t s has d e m o n s t r a t e d t h a t r a d i a t i o n - i n d u c e d interchange in i m m a t u r e oocytes directs the disjunction of the centromeres of the quasi-bivalent
I N T E R C H A N G E A N D N O N - I ) I S J U N C T I O N IN
D. lllclaJlogastgt"
OOCYTES
193
to opposite poles at the first meiotic division. In females without a Y chromosome interchange often involves the C(z)RM and a fourth chromosome. As a consequence the uninvolved fourth chromosome apparently behaves as a univalent and segregates at r a n d o m with respect to its normal pairing partner. One of the observed results of this altered segregation behavior is dose-dependent, interchange-mediated non-disjunction of the fourth chromosomes. These nullo-X, dilpo- 4 oocytes are recovered as one of the classes ot exceptional male progeny. When a Y chromosome is carried by the irradiated C(I)R3I females a high frequency of C(z)-5" interchange is observed along with a concomitant decrease in the frequency of C(z)-4 interchange. In addition, Y-4 interchange frequently (~ccurs and is recognized by the recovery of Y chromosome fragments showing linkage of Y and fourth chromosome markers. When the resultant Y-qR fragment is recovered in females it is usually recovered without a free fourth chromosome, implying t h a t the homologous fourth chromosome segregated to the opposite pole as did the C(z)RM and Y-4R fragment. One of the consequences of such segregations is the induction of nullo-X, haplo- 4 oocytes which are recovered as exceptional male progeny. In the present data these comprise the largest class of exceptional progeny (487). Irradiation of mature oocytes results in completely different disjunctional events as has been adequately demonstrated~,2s, 29. In C(z)RM/Y females the distributive pool is composed of the compt~und-X, the Y and the 2 fourth chromosomes. The c o m p o u n d - X anti the Y disjoin regularly; the fourth chromosomes are significantly smaller and also disjoin regularly. Disjunction of the pair of fourth chromosomes is at r a n d o m with respect to disjunction of the C(~)RM and Y chromosomes. An interchange between the C(z)R3I and one of the fourth chromosomes effectively removes one member of each pair of distributively paired chromosomes from the pool and directs the disjunction of the interchangeconjoined elements. A comparable situation ensues when the Y and one of the fourth chromosomes are interchange-conjoined. The behavior ol the Y and the uninvolved fourth chromosome in the first case and C(z)RM and the uninvolved fourth chromosome in the second case has not been previously analyzed. One prediction is that the uninw~lved chromosomes making up the modified distributive pool will re-associate and will disjoin from each other in a regular fashion and independently of the interchange quasi-bivalent. For example, in an oocvte with an induced C(])-4 interchange the Y chromosome and the uninw~lved fourth chromosome m a y form a "new distributive relationship" and disjoin from each other at first division. Since in the unincumbered situation the heteromorphic pair of sex chronmsomes and the pair of fourth chromosomes segregate at r a n d o m with respect to each other, the above prediction might be extended to expect that the "reconstituted" pair (Y and 4) would segregate at random with respect to the interchange-conjoined quasi bivalent. The predictions in Figs. i and 2 are based on the assumption t h a t removal of one member of each pair of distributively paired chromosc,mes allows a "re-association" of the remaining 2 chromosomes and that these 2 disjoin at r a n d o m with respect to the quasi-bivalent. The prediction from Fig. I is that an X-4R detachment will be recovered with a Y chronmsome and no free fourth chromosome as often as an X-4R detachment is recovered with a free (homologous) fourth chromosome and no Y chromosome (Fig. z ; Alb vs. Bxb). The data in Table I are convincing that this prediction doesn't hold. X-4R detachments recovered with a Y chromosome but no free fourth chromosome are
z94
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Fig. 1. Hypothetical segregation of chromosomes when an interchange conjoins the C(z)RM and a fourth chromosome and if the Y chromosome and the uninvolved fourth chromosome segregate from each other and independently of their regular disjunctive partners. Thin lines represent the C(z)R31, wavy lines represent the Y chromosome and thick lines represent the fourth chromosonles.
r e p r e s e n t e d z() t i m e s w h e r e a s X-4R d e t a c h i n e n t s r e c o v e r e d w i t h a free f o u r t h c h r o m o s o m e a n d n o Y a r e r e p r e s e n t e d 39 t i m e s . I n a d d i t i o n , X-4R d e t a c h m e n t s I e c o v e r e d w i t h n e i t h e r a Y n o r a free f o u r t h c h r o m o s o m e are r e p r e s e n t e d z 9 t i m e s , a n d in n o ease w a s a n X-4R d e t a c h m e n t r e c o v e r e d w i t h b o t h a free f o u r t h a n d a Y c h r o m o s o m e . Fig. 2 p r e d i c t s t h a t Y-4 i n t e r c h a n g e a n d s e g r e g a t i o n of t h e C(±)RM f r o m t h e u n i n v o l v e d f o u r t h c h r o m o s o m e w o u l d r e s u l t in r e c o v e r y of Y-4R f r a g m e n t s w i t h o u t a free f o u r t h c h r o m o s o m e as o f t e n as it w o u l d r e s u l t in r e c o v e r y of Y-4R f r a g m e n t s w i t h a free ( h o m o l o g o u s } f o u r t h c h r o m o s o m e . T h e f o r m e r w o u l d b e r e c o v e r e d in f e m a l e s a n d t h e l a t t e r w o u l d b e r e c o v e r e d in m a l e s (Fig. 2 ; A~b vs. B~b). A g a i n t h e d a t a in T a b l e I d o n o t s u p p o r t so s i m p l i s t i c a n i n t e r p r e t a t i o n of t h e c o n s e q u e n c e s of i n t e r c h a n g e s in i m m a t u r e o o c y t e s . T h e r e w e r e less t h a n h a l f as m a n y Y-4R/O f e m a l e s (23) as Y-4R/4 m a l e s (56) a m o n g t h e e x c e p t i o n a l p r o g e n y of i r r a d i a t e d f e m a l e s . I n a d d i DIVISION
'T
DIVISION
Tr
t
GAMETES a
b-
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B
B2
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Iqg. 2. Hypothetical segregation of chromosomes when an interchange conjoins the Y and a fourth chromosome, assuming t h a t the C(z)RllI and the uninvolved fourth chromosome segregate from each other and independently of their regular disjunctive partners. Thin lines represent the C(z)R31, wavy lines represent the Y chromosome and thick lines represent the fourth chromosomes.
INTERCHAN(~E AN1) NON DISJUNCTION IN D. inclauo~asler OOCYTES
105
tion, t h e r e were a b o u t as m a n v Y - 4 R / O m a l e s as t h e r e w e r e Y - 4 R / O females 119:23). T h o s e Y c h r o m o s o m e f r a g m e n t s for w h i c h t h e i n t e r c h a n g e p a r t n e r c a n n o t be d e t e r m i n e d ( Y . ?) were r e c o v e r e d a l m o s t e x c l u s i v e l y in m a l e s as was e x p e c t e d a n d were r e c o v e r e d w i t h o n l y one m a t e r n a l f o u r t h c h r o m o s o m e in e v e r y case. T h e d a t a in T a b l e 1 are q u i t e e x t e n s i v e c o m p a r e d w i t h t h o s e from p r e v i o u s e x p e r i m e n t s . F o r t h e m o s t p a r t t h e y v e r i f v t h e m a j o r details of t h e n a t u r e of t h e r e c o v e r y of r e c o m b i n a n t c h r o m o s o m e s f r o m i r r a d i a t e d females, yet s o m e differences are a p p a r e n t . D e t a c h m e n t s of t h e C ( I ) R M are u s u a l l y r e c o v e r e d e q u a l l y f r e q u e n t in t h e 2 sexes a n d this is t r u e in m o s t classes of d e t a c h m e n t s s m n m a r i z e d in T a b l e I. T h e X - } ' / 4 class, h o w e v e r , has a r e c o v e r y r a t i o ol I83 f e m a l e s to 97 males. A recessive l e t h a l carried b v t h e C ( r ) R M w o u l d e x p l a i n this d i s c r e p a n c y e x c e p t for t h e fact t h a t t h e o t h e r classes o{ d e t a c h m e n t s w o u l d be e x p e c t e d to d e m o n s t r a t e an m l e q u a l sex r a t i o a n d t h e y do not. T h e r e is no a p p a r e n t e x p l a n a t i o n for t h e u n e q u a l sex r a t i o in t h e X - Y class of d e t a c h m e n t s . A n o t h e r m i n o r d i s a g r e e m e n t of t h e d a t a in T a b l e I a n d p r e v i o u s d a t a is f o u n d in t h e sex r a t i o of Y-4 R recoveries. PARKER'S 1:1,15,16 d a t a in e l u d e d a s m a l l excess of m a l e s in t h e s e classes of e x c e p t i o n a l p r o g e n y while in T a b l e I t h e y are in a r a t i o of 32 females to 75 males. T h e s e d i s c r e p a n c i e s are n o t of i m p o r t a n c e h o w e v e r , in t h a t t h e y do n o t b e a r on t h e m a j o r q u e s t i o n s asked in this e x p e r i n l e n t . I t is o b v i o u s f r o m t h e s e c o n s i d e r a t i o n s t h a t i n t e r c h a n g e i n v o l v i n g tile C ( I ) R z l I and a fourth cllromosome and interchange involving the Y chronlosome and a fourth c h r o m o s o m e does n o t p r e c l u d e s e g r e g a t i o n of t h e C ( I ) R M a n d t h e Y c h r o m o s o m e s . I n d e e d , it a p p e a r s t h a t e v e n w h e n an i n t e r c h a n g e i n v o l v e s one b u t n o t t h e o t h e r of this pair of h e t e r o m o r p h s , t h e y t e n d to s e g r e g a t e from e a c h o t h e r m o r e 1ift e n t h a n not. In o t h e r words, d i s t r i t m t i v e p a i r i n g r e l a t i o n s h i p s of t h e C ( I ) t , LII a n d t h e Y c h r o m o sonles t e n d to be c o n s e r v e d e v e n w h e n C ( I ) - 4 a n d }'-4 i n t e r c h a n g e s are i n d u c e d . W h e t h e r or n o t t h e s e d a t a are i n d i c a t i v e of p r e - e x i s t i n g r e l a t i o n s h i p s b e t w e e n all of t h e m a n i t m l a t e d c h r o m o s o m e s is n o t clear. A e h r o m o c e n t r a l - l i k e r e l a t i o n s h i p of chron l o s o m e s in tile o o c y t e n u c l e u s has b e e n p r o p o s e d as one of the l e a s o n s t h a t t h e h e t e r o c h r o m a t i c regions of all of t h e c h r o n l o s o n l e s in t h e D r o s o p h i l a g e n o l n e call be i n v o l v e d in interchange12, 2v,'-'~, a n d r e c e n t l y a c h r o m o c e n t e r in t h e o n c v t e has been d e m o n s t r a t e d 2. A n y r e l a t i o n s h i p b e t w e e n an o v a r i a n c h r o m o c e n t e r a n d d i s t r i b u t i v e p a i r i n g r e l a t i l m s h i p s in i r r a d i a t e d females r e n l a i n s to be d e t e r m i n e d .
R 1':1:1':R KN(' I';S i V,ust~v, N., Segregation following interchall~e incluced by irradiating mature oocytes of Drosophila melanogaster, 3latation I¢,:s., 11 11971 ) 391 306. 2 I)AVRING, L., AND ~i. SI.'NNER, Fenlale meil)sis and enlbryonic mitosis in Drosophila melanogash'r, I. Meiosis and fertilization, Hereditas, 73 11973) 51 64. 3 (;nELL, E. H., Distributive pairi.ng lff compound chromosomes in females of Drosophila mclam~gaster, Gem,tics, 48 (19631 1217 I22% 4 (]RELL, R. 1:., A new model for secondary non disjunction: the role' of distributixc pairing, Genetics, 47 (1962) 1737-~754. 5 (;RI~LL, R. I:., The naeiotic origin of t~'mpcrature-induce(1 crossovers in Drosophila mHanogaster females, (;era'tics, 54 (10061 4 It 421. 0 (;RELI., R. F., Pairing at the chromosomal level..]. Cell Physiol., 7o, .Suppl. l (I9()~) 119 I40. 7 (;R~=LL, R. F., leeconlbination and I)NA replication in the Drosophila melanogaster oocyte, Gem'tics, 73 (~973) ~7 io8. S |',[IN(;, R. C., A. C. Ru~tNS/lX AXl) R. 1:. SMITH, ()o~4cnesis in adult Drosophila melanogasler, (;r,~wth, 2o (i056) I2I ~57.
196
J.H.
WILLIAMSON
9 LINDSLEY, i). L., AND ]?.. H. GRELL, Genetic v a r i a t i o n s of Drosophila melanogaster, Carnegie Inst. Wash. Publ., 627 (19681. 10 PARKER, D. R., R a d i a t i o n - i n d u c e d e x c h a n g e s in Drosophila females, Proc. Natl. dcad..';ci. (U.S.), 40 (19541 795-800. 1 I PARKER, D. R., On t h e n a t u r e of s e n s i t i v i t y c h a n g e s in oocytes of Drosophila melanogaster, in F. H. SOBELS (Ed.), Repair from Genetic Radiation Damage, P e r g a m o n , Oxford, 1963, pp. 11-19.
12 PARKER, l). R., Chronaosoine pairing a n d i n d u c e d e x c h a n g e in Drosophila, Mutation Res., 2 (1965) 523-529. 13 PARKER, D. R., I n d u c e d heterologous e x c h a n g e at nieiosis in Drosophila, I. E x c h a n g e s b e t w e e n Y a n d f o u r t h c h r o m o s o m e s , Mutation Res., 4 (1967) 333-33714 PARKER, D. R., A s u r v e y of m e t h o d s for t h e i n d u c t i o n of a b e r r a t i o n s in meiotic stages in Drosophila females a n d for o b s e r v a t i o n s of their d i s j u n c t i o n a l properties in t h e e n s u i n g meiotic divisions, in Effects of Radiation on Meiotic Systems, I n t e r n a t i o n a l A t o m i c E n e r g y Agency, Vienna, 1968, pp. 2o9 218. 15 PARKER, D. R., H e t e r o l o g o u s i n t e r c h a n g e at meiosis in Drosophila, II. Some d i s j u n c t i o n a l cons e q u e n c e s of interchange, Mutation Res., 7 (19691 393 4o7 • I6 PARKER, D. R., C o o r d i n a t e d n o n d i s j u n c t i o n of Y a n d f o u r t h c h r o m o s o m e s in irradiated coinp o u n d - X female Drosophila, Mutation Res., 9 (I97 o) 3o7-322. 17 PARKER, D. R., A,XD N. BUSBY, C h r o m o s o n l a l i n t e r c h a n g e in m a t u r e oocytes of Drosophila, Mutation Res., 16 (19721 49 58. 18 PARKER, D. R., AND N. BUSBY, O b s e r v a t i o n s c o n c e r n i n g t h e effects of r a d i a t i o n s on t h e segreg a t i o n of chronlosomes, Mutation Res., 18 (19731 33-46. 19 PARKER, D. R., AND A. E. HAM~IOND, T h e p r o d u c t i o n of t r a n s l o c a t i o n s in Drosophila oocytes, Genetics, 43 (I958) 9 2 - I ° ° . 2o PARKER, D. R., AND J. McCRONE, A genetic analysis of sonic r e a r r a n g e m e n e s i n d u c e d in oocytes of Drosophila, Genetics, 43 (19581 172-186. 2I PARKER, i). R., AND J. H. WILLIAMSON, Heterologous i n t e r c h a n g e at meiosis in Drosophila, III. I n t e r c h a n g e - m e d i a t e d n o n - d i s j u n c t i o n , Mutation Res., 9 (I97 o) 273-286. 22 SANDLER, L., D. L. LINDSLEY, B. NICOLETTI AXD G. TRIPPA, M u t a n t s affecting meiosis in nat u r a l p o p u l a t i o n s of Drosophila melanogaster, Genetics, 6o (1968) 325-528. 23 TRAUT, H., E x p e r i m e n t s on t h e m e c h a n i s m s of X - r a y induced c h r o m o s o n l e loss, Mutation Res., 6 (1968) lO9-115. 24 TRAUT, H., N o n d i s j u n c t i o n induced by X - r a y s in oocytes of Drosophila melanogaster, Mutation Res., IO (197 o) I 2 5 - I 3 2 . 25 TRAUT, H., AND W. SCHEnl, Cytological analysis of partial a n d total X - c h r o m o s o m e loss induced b y X - r a y s in oocytes of Drosophila melanogaster, Mutation Res., io (197 o) 583 589. 26 TRAUT, H., AND W. SCHEID, T h e p r o d u c t i o n of m o n o s o m i c - t r i s o m i c i n d i v i d u a l s in Drosophila melanogaster b y X - i r r a d i a t i o n of i m m a t u r e oocytes, 216rutation Res., 13 (1971) 429-432. 27 WILLIAMSOX, J. H., On t h e n a t u r e of Y c h r o m o s o m e f r a g m e n t s i n d u c e d in Drosophila rnelanogaster females, I. I m m a t u r e oocytes, Mutation Res., 8 (1969) 327-335. 28 WILLIA.~:SO.N, J. H., On t h e n a t u r e of Y c h r o m o s o m e f r a g m e n t s induced in Drosophila melanogaster females, II. M a t u r e oocytes, Mutation Res., 9 (197 o) 85-9o. 29 \VILLIAMSO~', J. H., Heterologous i n t e r c h a n g e a n d n o n d i s j u n c t i o n of d i s t r i b u t i v e l y paired c h r o m o s o m e s in Drosophila melanogaster. M a t u r e oocytes, Mutation Res., 18 (19731 273-277.