Sex and the chromosomes in the domestic fowl (gallus Domesticus)

The chromosome number in the domestic fowl is approximately thirty‐five or thirty‐six. It is difficult to determine the exact number, owing to the smallness of the shortest chromosomes of the complex and also to the tendency of the chromomeres to occasionally appear as discrete chromosomes rather than as parts of a whole. Difficulty experienced in fixing adult testes has prevented a satisfactory demonstration of all stages of spermatogenesis. However, satisfactorily preserved prophases of first spermatocytes have been observed which, together with the large amount of embryonic material available, have made it possible to work out the behavior of the sex‐associated chromosomes with reasonable certainty. Measurements of the chromosomes indicate that the longest chromosome in the cell is single in the female and paired in the male. Two classes of eggs are therefore possible—one with and one without this long chromosome, while all the spermatozoa produced are alike in possessing the long chromatic element. The female is therefore heterozygous and the male homozygous in regard to this chromosome which affords a cytological parallel for the genetic evidence of the heterozygosity of the female.