The present paper deals with the comparative morphology of the chromosomes in seventeen races of Domestic fowl,
Gallus gallus var.
domesticus, which was carried out with the purpose of finding whether any cytological difference is present or not among them, based on the morphological analysis of the chromosomes and the close comparison of the corresponding elements in them; the races under study are the Shamo, the Koshamo, the Chabo, the Totenko, the Shokoku, the White Leghorn, the Black Minorca, the Yukei (Buff Chinese fowl), the Light Sussex, the Ukokkei (the Chinese Silky), the Nagoya, the Mikawa, the Barred Plymouth Rock, the Rhode Island Red, the Buff Orpington, the Australorp, and the White Wyandotte.
(1) The result of the investigation shows that, so far as the general morphological characteristics of the chromosomes are concerned, the chromosome constitutions of the studied races are fairly identical with each other in all characters, not only in number of chromosomes and in the other morphological features. The number of chromosomes established was given in every race studied, as 78 in diploid and 39 in haploid in the male side and 77 in the diploid of the female.
(2) The constitution of the diploid complement is divided into two distinct size-groups, the macro-chromosomes and micro-chromosomes. The numbers of the macro-chromosomes are 16 in the male and 15 in the female (
a's to
h's), and consist of two homologous pairs of extremely large V-shaped elements (
a's and
b's), a pair of long rod-shaped ones (
c's), a pair of J-shaped ones having subterminal attachment (
d's), a medium sized distinct V-shaped element which is paired in the male cell and unpaired in the female cell (
e's), and three pairs of rod-shaped ones (
f's to
h's). The micro-chromosomes, 62 in number, all appear to he telomitic in structure and vary in shape from short rod to minute grainlike ones in a graded series. The sexual difference of chromosomes is found by the fact that the fifth largest V-shaped element labelled
e is destitude of its synaptic mate in the female cell, while it is paired in the male cell. By this evidence it is clear that the
e-chromosome under con-sideration is nothing other than the sex-chromosome.
(3) A close comparison was made based on the value of the ratio calculated in the length between the long arm and short arm of the
a- and
b-chromosomes respectively. The results presented indicate that the value of the obtained ratio is higher in the
b-element than in the a-element with-out exception in all the cases observed. The data are given in Tables 5, 6, and 9.
(4) The behaviour of germ-cells in testes of three kinds of interracial hybrids was observed and the results obtained prove that the chromosomes of these races are quite identical not only in their external visible feature but also in their inner genie constitution.
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