- Email: [email protected]
Cell Cycle
286
cD NA
This time-related reactivation has suggested that the mouse position effect variegation is not attributable to a progressive spread of inactivation into the insertion from the heterochromatic X, as hypothesized for Drosophila position effect variegation but, conversely, results from the progressive reactivation of the previously inactivated autosomal loci.
Uses of Translocation The translocation has been extensively used in diverse genetic and cytogenetic studies. In addition to providing the first recorded examples of the XXY condition in the mouse, selection studies upon the levels of variegation ultimately led to the recognition of the Xce locus and its control of the randomness of X inactivation. Xce effects have been investigated in both fetal and placental tissues using the translocation. The translocation has also been used in (1) diverse X-inactivation studies, (2) comparisonsofX-inactivation and chimerabased variegation, (3) biochemical studies upon gene dosage at the c locus, (4) creating flow sorted X chromosome libraries, (5) duplication mapping, (6) eye pigmentation studies, (7) investigations of the influence of pigmentation on the retinofugal pathways and, as a long marker chromosome, it has also been used in (8) cytogenetic studies on X inactivation, and (9) to investigate the single-cell origin of induced tumors. More recently, the translocation has been used to generate maternal duplication/paternal deficiency for the central region of chromosome 7 which creates a mouse model of the human imprinting condition, Prader± Willi syndrome. Currently, unbalanced (Type II) animals are being used to investigate the basis of autism found in humans with additional copies of the homologous region.
Further Reading
Cattanach BM (1961) A chemically-induced variegated-type position effect in the mouse. Zeitschrift fuÈr Verebbungslehre 92: 165±182.
See also: Nondisjunction; Translocation; X-Chromosome Inactivation
cDNA Y Kohara Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.1412
Complementary DNA (cDNA) is the DNA produced on an RNA template by the action of reverse
transcriptase (RNA-dependent DNA-polymerase). The sequence of the cDNA becomes complementary to the RNA sequence. Unlike RNA, DNA molecules can be cloned easily (these are called `cDNA clones') by making the cDNA double-stranded and ligated to a vector DNA. Sequence analysis of DNA is much easier than that of RNA, thus, cDNA is the essential form in the analysis of RNA, particularly of eukaryotic mRNA. Eukaryotic genes are fragmented (as exons) in the genomic DNA by the presence of intron sequences. When a gene is expressed, the entire gene region including the intron sequences is initially transcribed to RNA. Then the introns are removed (a process called `splicing') to generate mature mRNA which has a continuous set of triplets (three base genetic codons) corresponding to the amino acid sequence of the protein product. The pattern of splicing can be variable, leading to the production of different proteins from a single gene. This information is obtained mainly from cDNA analysis. Finally, cDNA clones are used for the production of proteins, using suitable expression systems such as bacteria, yeast, or animal cells. See also: DNA Cloning; Reverse Transcription
Cell Culture See: Tissue Culture
Cell Cycle D Lew Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.1557
In the first half of the nineteenth century, accumulating evidence from microscopic observations led to the recognition of cells as the fundamental building blocks of plant and animal tissues, and raised the question of how new cells are made. Pioneering microscopists witnessed the birth of new cells from the division of pre-existing cells, and repeated observation of cell division in many tissues firmly established that all cells arise by the division of parental cells. Indeed, over 150 years later, our appreciation of the complexity of cell organization makes it inconceivable that cells could arise in any other way. The means whereby self-replicating cells first evolved in the primeval soup remains one of the deepest mysteries in the origin of life, and even with our rapidly increasing technology and knowledge about what cells are made of, the goal
cD NA
This time-related reactivation has suggested that the mouse position effect variegation is not attributable to a progressive spread of inactivation into the insertion from the heterochromatic X, as hypothesized for Drosophila position effect variegation but, conversely, results from the progressive reactivation of the previously inactivated autosomal loci.
Uses of Translocation The translocation has been extensively used in diverse genetic and cytogenetic studies. In addition to providing the first recorded examples of the XXY condition in the mouse, selection studies upon the levels of variegation ultimately led to the recognition of the Xce locus and its control of the randomness of X inactivation. Xce effects have been investigated in both fetal and placental tissues using the translocation. The translocation has also been used in (1) diverse X-inactivation studies, (2) comparisonsofX-inactivation and chimerabased variegation, (3) biochemical studies upon gene dosage at the c locus, (4) creating flow sorted X chromosome libraries, (5) duplication mapping, (6) eye pigmentation studies, (7) investigations of the influence of pigmentation on the retinofugal pathways and, as a long marker chromosome, it has also been used in (8) cytogenetic studies on X inactivation, and (9) to investigate the single-cell origin of induced tumors. More recently, the translocation has been used to generate maternal duplication/paternal deficiency for the central region of chromosome 7 which creates a mouse model of the human imprinting condition, Prader± Willi syndrome. Currently, unbalanced (Type II) animals are being used to investigate the basis of autism found in humans with additional copies of the homologous region.
Further Reading
Cattanach BM (1961) A chemically-induced variegated-type position effect in the mouse. Zeitschrift fuÈr Verebbungslehre 92: 165±182.
See also: Nondisjunction; Translocation; X-Chromosome Inactivation
cDNA Y Kohara Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.1412
Complementary DNA (cDNA) is the DNA produced on an RNA template by the action of reverse
transcriptase (RNA-dependent DNA-polymerase). The sequence of the cDNA becomes complementary to the RNA sequence. Unlike RNA, DNA molecules can be cloned easily (these are called `cDNA clones') by making the cDNA double-stranded and ligated to a vector DNA. Sequence analysis of DNA is much easier than that of RNA, thus, cDNA is the essential form in the analysis of RNA, particularly of eukaryotic mRNA. Eukaryotic genes are fragmented (as exons) in the genomic DNA by the presence of intron sequences. When a gene is expressed, the entire gene region including the intron sequences is initially transcribed to RNA. Then the introns are removed (a process called `splicing') to generate mature mRNA which has a continuous set of triplets (three base genetic codons) corresponding to the amino acid sequence of the protein product. The pattern of splicing can be variable, leading to the production of different proteins from a single gene. This information is obtained mainly from cDNA analysis. Finally, cDNA clones are used for the production of proteins, using suitable expression systems such as bacteria, yeast, or animal cells. See also: DNA Cloning; Reverse Transcription
Cell Culture See: Tissue Culture
Cell Cycle D Lew Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.1557
In the first half of the nineteenth century, accumulating evidence from microscopic observations led to the recognition of cells as the fundamental building blocks of plant and animal tissues, and raised the question of how new cells are made. Pioneering microscopists witnessed the birth of new cells from the division of pre-existing cells, and repeated observation of cell division in many tissues firmly established that all cells arise by the division of parental cells. Indeed, over 150 years later, our appreciation of the complexity of cell organization makes it inconceivable that cells could arise in any other way. The means whereby self-replicating cells first evolved in the primeval soup remains one of the deepest mysteries in the origin of life, and even with our rapidly increasing technology and knowledge about what cells are made of, the goal