Showing papers on "Chromosome 22 published in 1970"

DNA and chromosomes

Abstract: DNA forms a Double Helix shape DNA is arranged in a double helix shape. The up rights of the “ladder” consist of alternating sugar and phosphate molecules bonded together. Making up the “rungs” are two base molecules bonded to each other. A nucleotide is one unit of DNA. DNA (deoxyribonucleic acid) is made from smaller repeating units called nucleotides, which consist of a sugar, a triphosphate and a base.

The discriminating fluorescence patterns of the chromosomes of Drosophila melanogaster.

Abstract: Mitotic and salivary gland chromosomes of D. melanogaster show striking fluorescent patterns when stained with Quinacrine. In the salivary gland chromosomes there are up to five strongly fluorescing bands located on the fourth chromosome and at the proximal end of the X chromosome.—In mitotic cells the Y chromosome shows four fluorescent segments and other fluorescent regions are found proximally on the third pair and on the X chromosome. It is, therefore, possible to distinguish male and female interphase cells by their patterns of fluorescence.—A comparison between the position of heterochromatic, late replicating and fluorescing segments in the mitotic chromosomes, shows differences which demonstrate, for the first time, the chemical, morphological and genetical diversity of these three types of segments.

Isolation of DNA from B Chromosomes in Grasshoppers

Abstract: A NUMBER of organisms have been reported to possess supernumerary or B chromosomes 1–3, although the origins and function of these chromosomes have largely remained an enigma. A large proportion of individuals in populations of the grasshopper Myrmeleotettix maculatus from the warmer and dryer parts of Great Britain contain B chromosomes in both germ-line and somatic cells. The frequency of individuals containing B chromosomes decreases in less favourable environments, and populations which live in even more stringent conditions, for example in Scotland, have none4. Individuals which possess these supernumerary chromosomes have an increased chiasma frequency and variance compared with standard grasshoppers in the same population5. Furthermore, this B chromosome is markedly heterochromatic during meiotic prophase.

Rearrangements between germ-line Limited and somatic chromosomes in Smittia parthenogenetica (Chironomidae, Diptera)

Abstract: Among more than 700 chromosome rearrangements induced by X-rays in oocytes of newly hatched females of Smittia parthenogenetica two cases of insertion of heterochromatin into an S chromosome have been obtained. As the S chromosomes do not contain such heterochromatic sections, the insertions must be derived from K chromosomes. Whether all K chromosomes are completely heterochromatic or whether all or some contain euchromatic sections remains open, but for the two latter possibilities no proof has been obtained. Euchromatic insertions or translocations with a banding pattern non-homologous with S chromosome sections have not been observed with certainty. Homologous duplications could all be interpreted as being derived from S chromosomes. From the K chromosome cycle it can be inferred that the K complement consists of more or less identical elements and that genetic isolation has led to their heterochromatinization.

Origin and Direction of Replication of the Chromosome of E. coli B/r

Abstract: The origin and direction of replication of the E. coli B/r chromosome has been determined by comparing gene frequencies in P1-transducing lysates prepared on cultures growing at different rates. The gene frequencies found are consistent with the idea that replication of the chromosome is dichotomous in rapidly growing B/r. The origin was found to be between 40 and 55 min on the E. coli genetic map with replication proceeding in a clockwise direction. Markers near the origin behaved anomalously.

Chromosome Number Variation in a Stick Insect Didymuria violescens (Leach)

Abstract: Seven major races, with diploid numbers ranging from 26 to 40, and three types of sex-chromosome mechanism were found in the Australian phasmatid Didymuria violescens (Leach). The differences between chromosome complements are mainly due to translocations between autosomes, and to translocations between autosomes and sex chromosomes. The geographic pattern of chromosome variation and the characteristics of hybrids implicate chromosomal rearrangements in mechanisms of speciation.

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.

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.

Human chromosome morphology. ii. studies on the satellites and identification of the large acrocentric chromosomes

Abstract: Chromosome measurements, centromeric position and short arm structure of the three large acrocentric autosomes in the human complement were investigated in somatic metaphases prepared from peripheral blood cultures. Chromosomes 13, 14 and 15 were arranged in descending order of their total length. The results of this study show that chromosome 13 has the lowest arm ratio and possesses a double satellite system, number 14 has the highest arm ratio and lacks satellites, and 15 has intermediate arm ratio and a prominent single satellite.

Chromosomal DNA replication pattern in human tumour cells in vitro.

Abstract: The present paper deals with the chromosomal DNA replication pattern in human solid tumour cells in vitro. This was studied at the terminal stages of the S-period. All the cell lines of female origin showed a late replicating chromosome in group XX6-12. In cell lines of male origin one of the chromosomes of group 21-22Y was later replicating than the rest of the members of the group. The DNA replication pattern of the autosomes and the sex chromosomes was similar to that of the cultured human leucocytes. The results of the present study show that the DNA replication pattern of the chromosome in neoplastic cells is basically unchanged despite the changes in the chromosome number and morphology. Therefore the abnormal behaviour of the neoplastic cells cannot be related to the changes in the pattern of the chromosomal DNA replication.