Abstract
One of the most striking and interesting variations existing among domestic fowls is the condition known as rumplessness, in which the birds have no tail. The present author had the opportunity to obtain at Sapporo five rumpless fowls, three hens and two cocks, in 1930 and 1932 (Table 1). They appeared sporadically as an occasional occurrence in a flock of normal-tailed White Leghorns (Figs. 1-2). A morphological study of these rumpless fowls made by the present author (Hayasi 1941) revealed that they completely lacked one or two synsacral vertebrae, the free caudal vertebrae and the pygostyle (Figs. 4-8). On this basis, their condition is to be referred to as complete rumplessness. Dunn ('25, '26) and Laudauer and Dunn ('25) reported that there are two types of complete rumplessness, one type being accidental rumplessness which is non-heritable in character, while the other is hereditary rumplessness and was inherited as a dominant trait in their genetical experiments.
With the five rumpless fowls herein obtained some genetical experiments were attempted by the present author, to see whether the rumpless character in this case showed the same type of inheritance as reported by the previous authors.
The mating of a rumpless hen with a normal-tailed cock which was firstly made, produced progeny with normal external appearance having completely developed tails. The result is given in Table 2. The data suggest that the rumpless character in this case may probably be inherited as a recessive trait. In the inter es matings of F1-fowls obtained in the above experiment, there were obtained 96 F2-offsprings which segregated in the approximate proportion of 3 normals to 1 rumpless (cf. Table 3); that is, segregation took place in monohybrid fashion.
Furthermore, the back-crossing attempted between F1-hen and a rumpless cock, one of the parent birds, produced normal and rumpless progeny in approximately equal proportions (cf. Table 4). These results are sufficient to conclude that the rumpless character in the present case is inherited by a simple, Mendelian recessive gene, which is symbolically designated as r. It is quite evident that the rumpless fowls used as parents in these experiments are homozygotes for this rumpless gene r.
