When the White Leghorn breed of chickens is crossed to the White Wyandotte breed

Question

When the White Leghorn breed of chickens is crossed to the White Wyandotte breed, all the F1 birds have white feathers. The F2 birds appear in the ratio 13 white: 3 colored. When the White Leghorn breed is crossed to the White Silkie breed, all of the F1 progeny are white and the F2 progeny appear in a ratio of 13 white: 3 colored. But when the White Wyandottes are crossed to the White Silkies all of the F1 progeny are colored and the F2 progeny appear in the ratio 9 colored: 7 white. a. How are feather colors inherited in these breeds? Assign genotype designations in your explanation. b. Show the genotypes of each of the three breeds. You can assume that each breed is pure breeding. c. What phenotypic ratio is expected in the progeny from trihybrid parents?

Explanation / Answer

a) Three loci involved---answert

One possess a dominant of color (I+) and the other two possess different recessive inhibitors (cc and oo).

Only genotype iiC-O- produces colored birds

All other genotypes produce white feathers

White Leghorn chickens are homozygous for a dominant allele C that produces colored feathers, but also homozygous for the dominant inhibitor allele at another locus (I) that inhibits color formation and prevents expression of C.

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White leghorns and White Wyandottes are crossed,

F1 chickens will have white feathers?

CCII x ccii -> CcIi

All of the chickens will be white because they have one copy of the dominant inhibitor, I

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CcIi         x CcIi

9 C-I- white

3 C-ii dark

3 ccIi white

1 ccii white

13 white :3 colored

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Another breed (White Wyandottes) are homozygous for both recessive alleles (ccii).

They make neither the pigment nor the inhibitor

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b) genotypes

White leghorns (CCOOII)

White Wyandott (ccOOii)

White silkie (CCoii)

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c) 5 white ;9 colored

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