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It has been shown that the Japanese Bantam breed of fowl carries the Creeper mutation or an allele of it. In matings of Japanese Bantams a much larger percentage of homozygous embryos generally survives to late developmental stages than in matings of ordinary Creeper fowl. In contradistinction to the situation in matings of ordinary Creepers, no preferential embryo mortality of heterozygous Creepers occurs in Japanese Bantam stock. The results of our breeding experiments suggest that the modified effect of the Creeper mutation in Japanese Bantams is caused by an incompletely dominant modifier linked with the Creeper factor.

In conclusion, it can be said that following crosses to Dorking fowl recessive rumplessness occurred in larger numbers of offspring, as far as all types of the abnormality are concerned (penetrance), and that incidence of complete rumplessness (expressivity) was significantly raised in comparison with the low degree of penetrance and expressivity in the original White Leghorn-derived stock. The opposite, at least as far as penetrance is concerned, was found in the descendants of crosses to Jungle fowl. These differences agree with what one might have expected if the innate tendencies of the two stocks to produce widely differing incidences of sporadic rumplessness and their similar divergence in response to rumplessness-inducing chemicals had had an influence on penetrance andexpressivity of the recessive rumpless mutation. If similar evidence can be obtained with other material, it should become possible to test, and perhaps verify the hypothesis that the occurrence of sporadic malformations with typical...

Shortness of the extremities in Dark Cornish fowls appears to be determined by several genetic factors, probably more than one of these being dominant over the long-legged condition. In short-legged Cornish tibia and tarsometatarsus are most strikingly shortened. The fibula is better developed than in ordinary chickens. One of the factors concerned in shortening of the long bones is lethal in homozygous condition. The lethal embryos die just before the end of the incubation period or are still living at hatching time but are unable to hatch. They show a striking shortening of the extremities. This lethal mutation is genetically independent of the Creeper mutation.

IT is a well-known fact that in man during childhood male mortality is higher than female mortality. This greater male mortality is responsible for a gradual decline of the sex-ratio from birth to puberty. It appears that no observations have been made as yet concerning the relation between postnatal mortality and sex-ratio in the domestic fowl. Since such information aside from its immediate interest may be of theoretical value for the explanation of selective mortality in general, we have undertaken to analyze the mortality rec-' ords for the first two months after hatching of the chicks, which at this station were hatched for experimental purposes during the years 1922 to 1930. Approximately 19,100 chicks were hatched during this nine-year period. About 9,500 chicks out of this total belonged to a large number of crosses which were made for the genetic analysis of various morphological characters, while the remaining 9,600 chicks were Single Comb White Leghorns-. The Leghorn chicks belonged to inbreeding experiments carried out by Dr. L. C. Dunn and were partly derived from brother by sister or half-brother by sister matings and partly from crosses between unrelated individuals. In tabulating the death records all cases of accidental death (due to crowding, predatory enemies, drowning, and so on) were omitted; these amounted to approximately 5 per cent. of the total mortality. There was also a small number of chicks which could not be sexed because they had lost their identification bands or were decomposed before they were found. Most of the chicks were hatched during March, April and May. There were some small hatches, however, which came off in January

Cyclopia and related malformations have been observed as a lethal condition of fowl. The more important facts and conclusions may be summarized as follows: 1. The morphological expression varied from a condition in which the upper beak was rudimentary to microcephaly. The whole gamut of defects is referred to as perocephaly. This is subdivided into two groups, viz. ‘rudimentary upper beak’, comprising the low-grade defects, and ‘cyclopia’, under which heading we include malformations ranging from synophthalmia to microcephaly. In the rudimentary upper-beak condition the premaxillary bones are lacking. On rare occasions such chicks hatched; they were always blind. Synophthalmia and cyclopia are associated with a proboscis above the median orbit. In more extreme conditions only a median pigment spot was present, there was no oral opening and the ears were closer to the ventral midline than normally (otocephaly). The most extreme cases were microcephalic without any indications of eyes, mouth or ears. 2. Perocephalic malformations made their first appearance inF 2 and later generations . of crosses between recessive rumpless fowl and representatives of the following three breeds: Silver Gray Dorking, Rhode Island Bed and Jungle fowl. In sibships which included any embryos with these malformations, the incidence was about 2–3%. When families with a different breeding history were intercrossed, the incidence of perocephaly rose to about 5 %, and upon combining the genotypes of all sources of origin the frequency became about 13%. The proportions of rudimentary upper beak and cyclopic embryos remained nearly constant during these changes in total incidence of perocephaly. After the 13% level of incidence had been reached, all but the smallest sibships contained perocephalic embryos. Significant heterogeneity of incidence continued, however, to exist between the individual sibships of pen matings. 3. Twenty-one sons of perocephaly-producing parents were tested in our experiments. All transmitted the malformations. 4. A rising incidence of perocephaly was associated with increased early embryo mortality. 5. The sex ratio appeared to be normal among perocephalic embryos of all grades. 6. A scrutiny of the data obtained during four years showed in three of them a highly significant seasonal trend, the incidence of perocephaly rising from early toward late spring. The causes of this trend remain uncertain. 7. The results of our breeding tests led to the following interpretation. The genetic factors responsible for the occurrence of perocephaly (possibly a single recessive gene substitution) were present in the stock of recessive rumpless fowl. Except for extremely rare ‘ sporadic’ occurrences, the mutation was completely suppressed by modifying genes. The mutation came to light after outcrosses to unrelated stocks and the incidence rose with continued dilution of protective modifiers. It is evident that even in later generations many embryos which were homozygous for perocephaly developed normally. 8. It is suggested that, in fowl at least, the accumulation of recessive modifying genes with individually small effects, but which in concert can completely suppress the action of deleterious mutants, represents a common and important mechanism of equilibration and genetic self-defence.

FLUCTUATIONS in the serum calcium level and in the degree of hyperossification of the long bones in the pigeon are correlated with ovarian function (1, 2). Similar changes also occur in sparrows in relation to the ovarian cycles (3), and follow the injection of estrogens in pigeons (4) and fowl (5, 6). Fowl, however, differ from pigeons in their response to estrogen in that the levels of serum calcium are much higher and hyperlipemia is grossly apparent. These differences in response might be associated with the fact that pigeons lay only 2 or 3 eggs in a clutch, whereas fowl lay more or less continuously. On this assumption, the amount of calcium and lipoid material mobilized under the influence of estrogen treatment would be to some extent proportional to egg production.

Linkage tests were made between the genes for single-comb and for the Creeper condition in fowl. Four geographically different lines or Creeper chickens were used in the matings. Chickens which were heterozygous for Creeper and rose-comb were crossed to others which were homozygous for the two recessive genes (normal skeleton and single-comb). Both heterozygous males and females were used in these back-crosses. The experiments extended over the first and second laying year. The total progeny of these matings amounted to 6627 individuals.

Breeding experiments in which selection was exercised against the lethal action of and the production of beak defects by the "short upper beak" mutation of fowl yielded the following results. The percentage of hatched chicks became nearly normal. In the final progeny the great majority of chicks had a normal beak at hatching time, and most of those chicks which at first had a slight shortening of the upper beak became normal during growth. In some instances the upper beak at maturity was longer than normal. The effect of the "short upper beak" mutation on long bone length became lessened under the influence of selection against lethal action and beak deformity. The "short upper beak" mutation was found in Houdan stock. The modifiers of this mutation were picked up after outcrosses to White Leghorn fowl. It is concluded that the "modifiers" are part of the normal genic make-up of beak development in the White Leghorn breed.

The duplicate mutation (Po d) of fowl is responsible for preaxial polydactylism of hand and foot Malformations of the radius occur frequently in association with finger duplication, These abnormalities can be arranged in series which in one direction lead by imperceptible steps from a slight hypoplasia to aplasia of the radius and which in the opposite direction proceed from the occurrence of small supernumerary rudiments to complete radius duplication. The duplicated radius may have a grossly abnormal, broad and flat shape with irregular outline.

Previous studies have shown that pigeons treated with estrogenic substances show a decided rise in blood calcium and a replacement of the marrow cavity by newly-formed endosteal bone.1 It seemed of interest, therefore, to study the effect of estrogen on the bones and on the blood calcium of the domestic fowl. While our experiments were in progress, Zondek reported that estrogens increase bone calcification and raise the blood calcium level of chicks of both sexes.2 These changes were associated with dwarfism.Our material consisted of fully-grown and sexually-mature cocks. We used normal and Creeper cocks, the latter belonging to a breed characterized by chondrodystrophy-like disproportionate dwarfism. Except for one cock, which was 9 months of age, the animals were about 6 to 7 months old when the injections were begun. The body weight of the animals ranged from 870 g to 1620 g at the beginning of the experiment. Nine Creeper and 6 normal cocks were treated with daily injections of estradiol benzoate ‡; 5...

THE only information concerning the primary sox ratio of birds, based on acceptable criteria, is to be found in a publication by Hays which relates to Rhode Island Red fowl1. Hays's results give the sexes in the progenies of 39 hens which in the course of a ten-year period had shown 100 per cent fertility and 100 per cent hatchability of their eggs during the two-months hatching season of one of these years. The 39 hens in question had a total of 931 offspring : 61 chicks were lost before the sex could be ascertained; among the remaining 870 chicks, 432 were males and 438 were females. These results clearly pointed to equality of the sexes as determined at fertilization. Yet, Hays suggested (see below), that significant differences may have existed between individual hens in the sex ratios of their offspring.

In 1934 Kyes and Potter reported the remarkable observation that cyclic changes in ossification of the long bones occur in pigeons parallel with, and indeed dependent upon, the alternations of ovarian activity. This was the first evidence for modifications of the skeleton brought about by estrogens, though it had been known that the serum calcium level may show such a dependence (Riddle and Reinhart, 1926). During the succeeding years extensive experimental work was conducted with mammals and birds relative to the effects of estrogens on ossification. With fowl tests of this nature were first made by Zondek (1936, 1937) and by Landauer, Pfeiffer, Gardner and Man (1939). A histological account of the changes observed in these experiments was given by Landauer and Zondek (1944). At that time (viz., 1941) an experiment was also conducted to determine the effect, as far as bone structure was concerned

Recently we have reported on linkage tests between the genes for single comb and for the creeper traits in fowl1. Afterwards, the back-cross matings of heterozygous rose-combed Creeper hens to Leghorn cocks were continued through the third laying year of the hens. During this period we obtained a total of 781 offspring (hatched chicks and classifiable dead embryos), distributed as follows: There was 0.38 per cent of crossing-over. These data added to our earlier ones bring the total off-spring of matings between heterozygous Creeper females and normal males to 4,313 individuals with 0.56 per cent of crossing-over, and the total offspring of all back-crosses to 7,408 chicks with 0.39 per cent crossing-over.