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.
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Answer:
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.
Explanation:
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