Canadian journal of genetics and cytology. Journal canadien de genetique et de cytologie最新文献

Eggs and larvae produced by diploid, triploid, and tetraploid females collected from breeding ponds on Pelee Island in Lake Erie were studied to examine the reproductive mechanism. No instance of parthenogenesis was found as all examined females required sperm to produce viable progeny. Diploid females produced diploid and triploid larvae, triploid females produced triploid and tetraploid larvae, and tetraploid females produced triploid and tetraploid larvae. The majority of the eggs produced by hybrid females do not develop or do not complete embryogenesis. Electrophoretic examination of females and their offspring demonstrate that the male genome is being incorporated in reduced as well as unreduced eggs produced by all three ploidy classes of females. The elevation of ploidy among Pelee Island Ambystoma is attributed to sperm incorporation in unreduced eggs. Triploid as well as tetraploid individuals are constantly being produced. A critical examination of the literature on parthenogenetic or gynogenetic modes of reproduction in North America Ambystoma hybrids shows no conclusive evidence supporting these modes and it is suggested that the reproductive mechanism found among Pelee Island female hybrids may be more generally applied to other hybrid Ambystoma populations.

Chromosome banding patterns obtained by silver staining and chromomycin a3 (CMA3) staining were analyzed in six species of Oncorhynchus: O. tshawytscha, O. kisutch, O. keta, O. nerka, and O. gorbuscha from North America and O. masou from Japan. Four different chromosomal locations of the nucleolar organizer regions (NORs) were found in different species. In O. tshawytscha, O. kisutch, and O. masou the NORs comprised the entire short arms of one medium-sized acrocentric chromosome pair. In O. nerka the NORs were found in an interstitial band on the short arms of one submetacentric chromosome pair and in O. gorbuscha proximal to the centromere on one metacentric chromosome pair. In O. keta the NORs were found on the telomeres of one small submetacentric chromosome pair. As in the related genera Salmo and Salvelinus chromomycin A3 positive bands were found at the same sites as the AgNORs in all species. Salmonid fish are assumed to be ancestral tetraploids and the considerable differences in chromosome number between different species are thought to be the result of chromosomal fusions after tetraploidization. In all members of the genus Oncorhynchus the rearrangements have resulted in the consolidation of the NORs on a single chromosome pair. The possible significance of intra- and inter-species NOR polymorphisms is discussed.

It is well known that there is a strong influence of fixation, i.e., acetic methanol versus formaldehyde, on the chromosome morphology at stages of the first meiotic division. In this study the influence of both these types of fixation on the morphology of mitotic chromosomes was examined in human lymphocytes. After methanol-acetic acid (3:1) fixation, the chromosomes show the "classical" condensed shape in which it is not always possible to recognize the two sister chromatids. These chromosomes are accessible to the conventional G-, R-, and C-banding techniques. After formaldehyde fixation at a relatively high pH, the chromosomes are thinner and longer (two to six times) when compared with chromosomes following methanol-acetic acid fixation. They show a scaffold-like morphology, sometimes with a halo of thin material around it. In all cases the two sister chromatids could be recognized. This chromosome structure could be easily stained with silver, Giemsa, 4,6-diamino-2-phenyl-indole (DAPI), and fluorescein isocyanate isomere 1 (FITC). The results obtained following these stainings gave no indication to any specific chemical composition of a probable central scaffold. The scaffold-like structures were not accessible to G-, R-, or C-banding techniques. The only effect observed following these banding techniques was the disappearance of the halo of thin material around the central scaffold-like structure.