Showing papers on "Chromosome 21 published in 1970"

Heritable Fragile Site on Chromosome 16: Probable Localization of Haptoglobin Locus in Man

Abstract: We have found recurrent chromosome breaks at a site (the "fragile site") on the long arm of chromosome 16. This site segregates in simple Mendelian dominant fashion in a large family. The distal portion of the chromosome sometimes shows selective endoreduplication. Preliminary linkage results reveal only 3 recombinants in 33 opportunities for recombination between the fragile site and the alpha locus of haptoglobin, an indication that the alpha-Hp gene is located near this region on chromosome 16.

Genetic activity of sex chromosomes in somatic cells of mammals

Abstract: Mammals are thought to have a type of dosage compensation not so far known in any other animal group: however many X chromosomes are present, only one remains genetically active in somatic cells. Considerable evidence for this idea exists, in spite of criticism; the greatest difficulty is presented by the abnormalities in human individuals with X chromosome aberrations. Possible explanations for these abnormalities include: wrong X chromosome dosage in early development before X inactivation, reversal of inactivation, partial inactivation of both X chromosomes, activity of the X while in the condensed inactive state, and the presence of a homologous non-inactivated region of the human X and Y. In female germ cells X inactivation apparently does not occur, but the situation in male germ cells is less clear. The Y chromosome is probably also inactive in somatic cells of adults, but again its function in germ cells is not yet clear. Some species have a presumed doubly inactive X chromosome region, as well as the singly active one. The origins and functions of this region are unknown; it may have a role in female germ cells.

Late DNA replication in male mouse meiotic chromosomes.

Abstract: Parts of the male mouse meiotic complement comprising the Y chromosome, the whole X chromosome, and near-centromeric parts of autosomal bivalents are synthesized late, as judged by tritiated thymidine autoradiography. This confirms the occurrence of end-to-end association between X and Y chromosomes and suggests that paired heterochromatic segments in autosomes must synthesize DNA at the same time.

Replication of the mouse sex chromosomes early in the S period

Abstract: The late-replicating X of the mouse can be clearly identified in a large proportion of metaphase spreads as an unlabelled chromosome when labelling of cells is done early in the S period. The Y chromosome follows this same pattern. Studies on Cattanach’s translocation are also reported, and it has been shown that the Xt can be distinguished from the normal X in early labelled material.

Population cytogenetics, assignment of gene loci in autosomes, karyotype-phenotype correlations. A progress report on human cytogenetics.

Abstract: This review summarizes three areas of human cytogenetics: 1. Studies of over 10,000 unselected live-born infants from four different series reveal an incidence of chromosomal aberrations of 1:200. About 50% of anomalies involve the chromosome structure; abnormalities of the sex chromosomes and the autosomes occur with equal frequency; about 50% of infants with a chromosomal aberration are clinically inapparent. The most frequent numerical anomalies are the XXY- and the XYY-condition, and the most frequent structural aberration is the translocation DqDq between two chromosomes of group D. According to work of Lubs and Ruddle, minor variants of the normal karyotype occur in the different chromosomal groups with following frequencies: A-group: 1.1%, B-group: 0.04%, C-group: 0.16%, D-group: 16.9%, E-group: 4.2%, F-group: 0.08%, G-group: 6.2%, Y-chromosome: 5.6%. Recent studies of the familial translocation DqGq disclose a smaller than expected risk for trisomie offspring to translocation heterozygotes: about 15–18% for female and 2–3% for male carries of this translocation. 2. Several studies concerning the assignment of gene loci to autosomes are reviewed. At present, the following genes could be assigned to human autosomes with varying degrees of certainty: (I) Duffy blood group and congenital zonular pulverent cataract on or near the proximal long arm of chromosome 1; (II) MN locus on chromosome 4 (distal long arm) or chromosome 2 (middle of long arm); (III) Gc factor on chromosome 4 or 19\2-20; (IV) Hageman blood clotting factor on the short arm of chromsome 6; (V) Haptoglobin alpha chain locus on chromosome 16; (VI) thymidine kinase locus on a chromosome 17 or 18. In addition, there are some as yet inconclusive data supporting a possible association of the erythrocyte acid phosphatase and chromosome 2; triosephosphate isomerase and the short arm of chromosome 5; chromosome 18 and immunoglobulin A production; chromosome 21 and the Lewis red cell antigen (a). It is emphasized that nearly all of these assignments must be considered tentative. 3. Probably three further deletion syndromes could now be recognized clinically: (I) The partial deletion of the short arm of chromosome 18 (18p-), (II) patients with a ring-D(? 14) chromosome, and (III) patients with a partial deletion of the long arm of chromosome 13.

Chromosome Structure and Function in Man, III. Pachytene Analysis and Identification of the Supernumerary Chromosome in a Case of Down's Syndrome (Mongolism)

Abstract: Recently developed pachytene maps of the two small acrocentric autosomes (numbers 21 and 22) of man have been applied to a case of Down's syndrome mosaic for normal and trisomic cells (46,XY/47,XY,21+). Trivalents in trisomic spermatocytes, and thus the supernumerary chromosome, were recognized as compatible in length and chromomere pattern with the shorter of these two chromosomes at the pachytene stage. With the exception of the region of the centromere and the short arm, association among constituents of the trivalent appeared complete.

Chromosomes in trisomy 21

Abstract: So much work has been devoted to the chromosomal study of trisomy 21 that it seems unnecessary to add to it. Nevertheless, the organizers of this conference have rightly believed that research was probably not complete, since we do not yet know why, how and when the chromosomal aberrations appear. Before focusing our attention on this most important point for the understanding of the causes of the disease, we can briefly summarize the general data now established in regard to many thousands of trisomics.

X-ray-induced recombination in the fourth chromosome of Drosophila melanogaster females. II. Segregational properties of recombinant fourth chromosomes.

Abstract: X-ray-induced recombinant fourth chromosomes exhibited a wide range of nonrandom associations with the reversed metacentric compound-X chromosome in C( i )RM/o females. The addition of a Y chromosome altered the degree of association, often randomizing segregation of the recombinant fourth chromosome and the compound-X. In some cases, however, the addition of a Y chromosome caused the recombinant fourth chromosome and the compound-X chromosome to segregate together less often than random. We have concluded that X-ray-induced recombination is an interchange process involving breakage and rejoining of homologues. These breaks need not be precisely between homologous loci and may lead to small duplications and deficiencies. Therefore an “induced crossover” chromosomes is in reality a kind of “half-translocation”. Whether the observed variations in nonrandom associations are due to differences in mere size or differences in genetic content of the centric regions of the recombinant chromosome is problematical.