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Chen et al. identified 132 whole-genome duplications (WGDs) clustered around environmental crises. We highlight how, over longer evolutionary timescales, ancient WGDs convergently retained MADS-box, MYB, WRKY and HSF transcription factors, building stress-adaptation networks. These insights guide climate-resilient crop improvement through comparative genomics and CRISPR engineering.
Ehrlich ascites tumor cells from the plateau phase of growth were transplanted into new hosts, pulse-labeled with tritiated thymidine and blocked with repeated injections of vinblastine. When unlabeled cells were analyzed for their cellular DNA content utilizing a cytophotometric technique it was found that in relation to the total number of cells (labeled plus unlabeled), 13% had a 2C DNA content, 36% a 4C DNA content and 5% and 8C DNA content at 0.5 hours after tranplantation. By 24 hours the distributions changed dramatically: the initally unlabeled 2C cells were now 4C, the 36% of the cells that were initially 4C partitioned into 24% that were still 4C and 12% that progressed to 8C, and the initial 8C cells remained 8C. These studies indicate that the accumulation of 4C cells during the plateau phase of growth is due to a combination of G2 diploid and G1 tetraploid cells.
The mutation rate to thioguanine resistance was 3.11 X 10(-6) in a near diploid V79 hamster cell line and 7.58 X 10(-8) in a near tetraploid derivative produced with colchicine. The specific activities of glucose-6-phosphate dehydrogenase and phosphoglycerate kinase of the tetraploid line were greater than that of the diploid which suggests that twice the number of active X chromosomes were present in the tetraploid. These results are compatible with the hypothesis that spontaneous variants resistant to thioguanine arise through mutation and chromosomal segregation, as has been suggested for induced mutations in tetraploid hamster cells.
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Satellite DNA amounts were examined in adult tissues of Drosophila virilis, a species whose DNA contains three prominent satellites. Satellite amounts in DNA from six of the seven tissues were lower than in DNA from diploid (adult brain) tissue. Satellite amounts in adult ovary DNA, however, were equivalent to or greater than diploid levels. When DNA from pupal ovaries was examined, a 30% increase in satellite amounts over diploid levels was found. An RNA-DNA hybridization experiment showed that the ribosomal RNA genes in pupal ovary DNA were under-replicated relative to diploid DNA levels.
C-band patterns of some Odontophrynus species from Brazil are described. O. americanus 2n and 4n are cryptic species similar to O. cultripes 2n, but their C-banding patterns are different. In O. americanus 2n the C-band appears at the secondary constriction of chromosomes 4. In O. americanus 4n and O. cultripes the C-band appears at the secondary constriction of chromosomes 11. O. cultripes chromosomes 2,3 and 6, have also an intercalary band. Furthermore, fine centromeric bands in several weeks old preparations of these species were observed. The possibility of a structural or chemical heterogeneity of those heterochromatic regions is discussed.
The DNA analysis of rat brain nuclei by two independent cytochemical methods, namely microfluorometry and UV-absorption, brings completely different results to those published previously by many investigators. The neuronal nuclei possess twice as much DNA as the glial nuclei.
2 new species of the anuran genus Xenopus have been found in western Uganda: X. ruwenzoriensis sp.n. with the hexaploid chromosome number of 108 in the Semliki Valley, west of the Ruwenzori, and X. species nova with the tetraploid chromosome number of 72 in and near lake Bunyoni.
The state of ploidy of 4c hepatocytes is examined by kinetic analysis of DNA reassociation. The nucleotide sequences present in 4c hepatocyte DNA are found to be complementary to, and present in the same relative abundance as, those of the normal diploid genome. Therefore, these experiments indicate that the increased DNA content of 4c hepatocytes is due to the presence of four haploid genomes and not to selective replication of a subfraction of the diploid genome. The concept of ploidy, typically defined in terms of karyotypic and/or DNA content multiples is thus corroborated and extended by these experiments.
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