Question

. In chickens, silver and gold feathering is determined by a single pair of alleles as is slow and rapid feather development. True-breeding males that were silver, slow feathered were crossed with true-breeding females that were gold, fast feathered. All F1 were silver, slow feathered. The F2 phenotypes were as follows: 300 male progeny were silver, slow feathered; 120 females were silver, slow feathered; 123 females were gold, rapid feathered 35 females were silver, rapid feathered; and 32 females were gold, slow feathered.

Explain the different results obtained for females and males.

Are the two genes linked or independently segregating? Explain.

On which chromosomes, autosomes or sex chromosomes, are the traits located? Be specific.

Answer 1

Ratio of progenies in F2 :

Silver slow male = 300

Silver slow female = 120

Gold rapid female = 123

Silver rapid female = 35

Gold slow female = 32

# silver slow = 300 + 120 = 420

# gold slow = 32

# silver rapid = 35

# gold rapid = 123

Ratio = 420/32, 123/32, 35/32, 32/32 = 13.1, 3.84, 1.09, 1

There is a different for males and females because the genes would have been located on chromosome. In case of X linked traits the results of second generation for males and females are different.

The ratio obtained in this obtained for 2nd generation is not the classical mendelian ratio. Therefore we can say that the genes are not showing mendelian pattern of inheritance. Therefore they will not show independent assortment. In this case there is said to be linked and will show linkage.

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