Black Langshan chickens have feathered shanks (part of the leg). White leghorns
ID: 55165 • Letter: B
Question
Black Langshan chickens have feathered shanks (part of the leg). White leghorns have naked shanks. Pure-breeding Langshans were crossed to pure-breeding White Leghorns and the F1 all had feathered shanks. The F1 were crossed to one another and produced 448 F2 progeny. Of these, 27 were found to have naked shanks, while the remaining 421 had feathered shanks. What is the most likely mode of inheritance for the difference (feathered vs. naked shank) in these chickens? Explain your answer by showing the genetics of the cross (NB: the concept of reduced penetrance is NOT involved here).
Explanation / Answer
Consider the genotype of Black Langshan chickens have feathered shanks as "FF," and the genotype of white leghorns with naked shanks is NN. True breeding between these two give the offpsring (F1) with the following genotypes.
FF* NN = FN (100%). Cross between F1 gives F2 progeny.
Thus, F2 offspring are, FN* FN = FF (feathered), FN (feathered), FN (feathered), NN (nacked). (Since, F is dominant to N).
Thus, the expected genotypic ratio of feathered to nacked phenotype is, 3:1 (3/4 feathered, 1/4 nacked). But, this is deviating from the given progeny phenotype. It is given that 27 were found to have naked shanks, while the remaining 421 had feathered shanks.
This is because the F and N are linked genes, and they undergo recombination. The percent recombination ferquency is = 27/448* 100 = 6%.
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