Articles written in Journal of Genetics
Volume 22 Issue 1 April 1930 pp 95-101
Volume 23 Issue 3 December 1930 pp 397-413
Volume 25 Issue 3 April 1932 pp 367-394
Volume 26 Issue 2 October 1932 pp 285-290
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.
The results show that linkage between the genes for Creeper and single-comb is very close, the frequency of crossing-over in the whole material amounting to 0·36 per cent. The data suggest that crossing-over occurs more frequently in females (0·57 per cent.) than in males (0·13 per cent.). No definite relation could be established between age and crossing-over. The Creeper characters of all four lines which were used for the crosses appear to be due to an identical mutation.
On the basis of our present knowledge it seems likely that the Creeper condition is caused by a section deficiency of the chromosomes in which the comb allelomorphs are located.
Volume 29 Issue 2 July 1934 pp 217-243
Volume 30 Issue 2 March 1935 pp 303-320
Volume 31 Issue 2 August 1935 pp 237-242
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.
Volume 33 Issue 3 December 1936 pp 401-405
Volume 37 Issue 1 December 1938 pp 51-68
Volume 54 Issue 2 May 1956 pp 199-218
The duplicate mutation (
Volume 54 Issue 2 May 1956 pp 219-235
Cyclopia and related malformations have been observed as a lethal condition of fowl. The more important facts and conclusions may be summarized as follows:
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.
Perocephalic malformations made their first appearance in
Twenty-one sons of perocephaly-producing parents were tested in our experiments. All transmitted the malformations.
A rising incidence of perocephaly was associated with increased early embryo mortality.
The sex ratio appeared to be normal among perocephalic embryos of all grades.
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.
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.
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.
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