Abstract
An understanding of the action of hereditary factors in regulating structural expression is likely to be facilitated by finding ways of reproducing the same effects by other than genetic means. To this end, the conditioning of either of 2 allelomorphic forms irrespective of the genotype is a principal desideratum. The present note records the few fragmentary data obtained from an attempt in this direction. Suppression of several of the sacral and caudal vertebrae in the fowl producing the condition known as “rumplessness” has long been known, and has been studied by Du Toit, 1 Dunn, 2 and Landauer, 3 who have described the anatomy and genetics of the condition. The latter authors have also pointed out the occurrence of occasional spontaneous non-hereditary cases which differ little, if at all, from those of the hereditary type. Owing to the extreme rarity of the sporadic cases (not over 1 in 1000, according to Dunn), it has hitherto seemed improbable that much could be learned of their genesis.
The simultaneous appearance of 3 such cases among a small number of chicks hatched for another experiment suggested a search for the cause of the anomaly. Since the abnormal chicks were from artificially incubated eggs, the occurrence of some disturbance before or at the time of most rapid differentiation of the caudal end of the embryo seemed probable. Consequently tests were made in which the temperature was varied in different ways during the first 6 or 7 days of incubation. In one series it was possible through the kindness of Dr. Landauer to test eggs from fowls which were hereditarily rumpless, and should consequently be expected to produce a considerable proportion of rumpless chicks (Dunn and Landauer).
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