Chromosome 21

About: Chromosome 21 is a research topic. Over the lifetime, 4736 publications have been published within this topic receiving 206655 citations. The topic is also known as: chr21 & Homo sapiens chromosome 21.

A Mouse Translocation Giving a Metacentric Marker Chromosome

Abstract: The paper describes genetic and cytological studies of mice carrying a sub-metacentric chromosome, apparently formed by the combination of a medium-sized acrocentric chromosome with a small one having

The repair of X-ray induced chromosomal damage in trisomy 2-and normal diploid lymphocytes.

Abstract: The frequency of chromosomal aberrations produced by X-rays is greater in lymphocytes cultured from trisomy 21 patients (Down's syndrome) than from normal diploid donors. This increase, which can be detected by a micronucleus assay for chromosomal damage, was postulated by us to result from a defect in the rejoining system which repairs chromosomal breaks. The postulated defect would result in a longer rejoining time, therapy permitting more movement of broken ends and thus enhancing the frequency of exchanges. To test this possibility, the time required for the rejoining (repair) of chromosome breaks was measured in lymphocytes from five Down's syndrome (four trisomy 21 and one D/G translocation partial trisomy 21) donors, from a monosomy 21 donor, and from five diploid donors. The rejoining time was reduced in the Down's syndrome lymphocytes in comparison to the normal diploid and monosomy 21 lymphocytes. Thus the repair of chromosome breaks, far from being defective as evidenced by a longer rejoining time in Down's syndrome cells, occurred more rapidly than in normal cells. A mechanism is proposed by which reduced rejoining times would increase aberration frequencies as a consequence of competition between a (hypothetical) error-free repair system and the error-prone repair system that generates chromosomal aberrations. We suggest that the alteration in the rejoining of chromosomal aberrations may underlie the increased susceptibility of people with Down's syndrome to leukemia.

Normal phenotype with paternal uniparental isodisomy for chromosome 21.

Abstract: Uniparental disomy (UPD) involving several different chromosomes has been described in several cases of human pathologies. In order to investigate whether UPD for chromosome 21 is associated with abnormal phenotypes, we analyzed DNA polymorphisms in DNA from a family with de novo Robertsonian translocation t(21q;21q). The proband was a healthy male with 45 dup(21q) who was ascertained through his trisomy 21 offspring. No phenotypic abnormalities were noted in the physical exam, and his past medical history was unremarkable. We obtained genotypes for the proband and his parents' leukocyte DNAs from 17 highly informative short sequence repeat polymorphisms that map in the pericentromeric region and along the entire length of 21q. The order of the markers has been previously determined through the linkage and physical maps of this chromosome. For the nine informative markers there was no maternal allele contribution to the genotype of the proband; in addition, there was always reduction to homozygosity of a paternal allele. These data indicated that there was paternal uniparental isodisomy for chromosome 21 (pUPiD21). We conclude that pUPiD21 is not associated with abnormal phenotypes and that there are probably no imprinted genes on chromosome 21.