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The parental source of heteroploidy in chick embryos determined with chromosomally marked gametes

Summary. Males homozygous for chromosomal translocations were mated to karyologically normal females. The resulting embryos, after incubation for 16–18 h, were prepared for cytogenetic analysis. Of the 692 embryos analysed, 54 (7·8%) were heteroploid or contained a major heteroploid cell line. Each of the 638 normal 2n embryos contained one marker and one normal chromosome, indicating that none arose from gynogenesis. Thirteen homogeneous haploid embryos were identified; 24 embryos were chimaeric 1n/2n and one was 1n/3n. All haploid cell lines contained a marker chromosome indicating androgenetic origins. The 9 homogeneous triploid (3n) embryos and the 3n cell line in a single 1n/3n embryo contained a single marker. All resulted from fertilization by single spermatozoon of eggs that were diploid as a result of suppression of the second meiotic division. The 3n lines of two 2n/3n embryos were derived from other mechanisms. A single homogeneous tetraploid (4n) embryo and the 4n cell lines of three 2n/4n mosaic embryos each contained two marker chromosomes and presumably resulted from failure of cytokinesis in an early cleavage division.