Incidence and origin of heteroploidy, especially haploidy, in chick embryos from intraline and interline matings

Abstract

Preparations for chromosomal analysis were made from 2107 chick embryos at 16 hours of incubation. The embryos resulted from intraline and reciprocal interline matings of two genetically different stocks (AG and D6). The two stocks had been previously characterized as producers of high (AG) and low (D6) frequencies of chromosomally aberrant embryos. The overall frequency of aberrant embryos was 4.0 ± 0.42 %. The types and frequencies of abnormalities were: haploidy and haploid-euploid mosaics, 57 %; polyploidy and polyploid-diploid mosaics, 19%; aneuploidy, 17%; aneuploid-diploid mosaics, 5%; and structural aberrations, 2 %. Although there were no significant differences among the four types of matings in the overall frequency of heteroploid embryos (P > 0.1), a significant difference (P < 0.01) in the frequency of haploid and haploid-euploid mosaic embryos was found. The difference was entirely attributable to the line of dam; D6 dams had 1.2% and AG dams had 2.7 % haploid and haploid-euploid mosaic embryos. The difference between lines of sires was not significant. In addition, there was evidence of nonrandom distribution, among dams of both lines, of haploid and haploid-euploid mosaic embryos. It was concluded that the genotype of dam is an important influencing factor in the production of haploid cell lines in embryos. The superfluous genome in triploid embryos is usually maternal in origin, resulting from retention of the second polar body in the ovum. Sex-chromosome aneuploidy in chick embryos apparently derives from nondisjunction at meiosis I of oogenesis. The sex proportion of 2023 chromosomally sexed, diploid embryos was 50.2 ± 1.1 % male. No significant heterogeneity was observed among the types of matings. Sex proportion was not significantly influenced by any of a number of nongenetic variables.