Chromosomes of chicken-pheasant hybrids

Abstract

Chromosome analysis on 34 hybrid embryos obtained by two way crosses between Columbian Rock chickens (Gallus domesticus) and ring-necked pheasants (Phasianus colchicus) revealed that a majority of the embryos carry a haploid set each of chicken and pheasant chromosomes. Three of the male embryos resulting from chicken female-pheasant male crosses were cytogenetically indistinguishable from male domestic chicken whereas two embryos obtained from a similar cross, were chimeras composed of chicken cells and hybrid cells. The presence of hybrid embryos of chicken karyotype is attributable either to parthenogenesis in the hens or to fertilization of the hens ovum by rooster spermatozoa from previous matings, surviving in the female reproductive tract. It is postulated that the chimeric hybrids may be the result of double fertilization of the ovum and its retained polar body, and that the spermatozoa from the semen invested during this investigation and the rooster spermatozoa remaining viable in the hens oviduct from previous matings, were probably involved in this process. Studies on intergeneric hybrids obtained by crossing ring-necked pheasant and Columbian Rock chickens have shown that only less than thirty percent of the eggs laid were fertile (B ASRUR , ig6g ; B H AT N AGA R , 19 68). It was observed that among the fertile eggs incubated, over fifty percent died at various times before hatching (B ASRUR , ig6g). The exact reason for the high mortality rate in chicken-pheasant hybrids is not known although it is generally noted that the hybrid progeny are at great developmental disadvantage if the two species involved in hybridization are dissimilar in their cytogenetic make up (B ENIRSCHKE , et al., ig6 5). Higher fertility has been reported in matings of domestic chicken roosters to pheasant females than that noted in reciprocal crosses (A SMONDSON and Lox!rrz, 1957) although hatcha-bility was noted to be much lower in the chicken male-pheasant female crosses