Chromosome abnormalities in chicken (Gallus domesticus) embryos: types, frequencies and phenotypic effects.

Abstract

Cytological screening of 4182 chick embryos from 10 strains and 5 strain crosses was performed to determine the types and frequencies of chromosome abnormalities. Gross phenotypic effects, such as growth retardation and malformation, were noted. Clues to the etiology of such chromosome aberrations were also sought. The following euploid series was observed: Haploid mosaics (A-Z/2A-ZZ, A-Z/2A-ZZ/3A-ZZZ, A-Z/A-W/2A-ZW/2A-ZZ, A-Z/A-W/2A-ZW/ 3A-Z?), diploid (2A-ZZ and 2A-ZW), triploid (3A-ZWW, 3A-ZZW, 3A-ZZZ, 3A-ZZZW) and tetraploid (4A-ZZWW and 4A-ZZZZ). Aneuploidy was observed as follows: Trisomy for chromosome numbers 1, 2, 3, 4 and double trisomy 2/5. Trisomy-4 with deletion of 50% of the long arm of one member of the trisomic triplet was observed. A 3A-ZWW embryo was found with two cell populations: one, disomic for chromosome 2 and 6; the other, tetrasomic for 2 and 6. Of the 4182 embryos sampled 1.4% were haploids, 97.5% diploids, 0.8% triploids, 0.1% tetraploids and 0.2% trisomics. On the average 10.8% of the early dead embryos were euploid (excluding diploid) or aneuploid. However, the range for euploidy and aneuploidy among strains was 2.3–23.7% of early deads. Haploid embryos were consistently underdeveloped at 4 days of incubation (D.I.), and died by 5–7 D.I. About 90% of (36) triploid embryos died at or before 4 D.I. The remaining 10% (normal embryos) died prior to hatching. Trisomic embryos were dead or underdeveloped at 4 D.I. Tetraploidy appeared to be lethal at a very early stage. The various strains examined had different overall rates of chromosome aberrations (0.4–8.9%), and also showed different varieties of such aberrations. The modes and possible causes of meiotic, mitotic and fertilization errors are considered. Genetic control of chromosome abnormalities, particularly haploidy, is postulated.