We perform the following three crosses with silkworms: A translucent male crosse

Question

We perform the following three crosses with silkworms: A translucent male crossed with a wild type female, what are the parental genotypes for this cross? Draw the Punned square and list the expected phenotypic ratios. A homozygous wild type male crossed with a translucent female, what are the parental genotypes for this cross? Draw the Punned square and list the expected phenotypic ratios. A heterozygous wild type male crossed with a translucent female, what are the parental genotypes for this cross? Draw the Punned square and list the expected phenotypic ratios.

Explanation / Answer

Unlike XX-XY sex determination system where XY is heterozygotic male in the silkworm (Bombyx mori), heterozygotic genotype is for female i.e. ZW in the ZZ-ZW system and the male is the homogametic (ZZ).

Translucent skin (Zod) is the Z-linked trait; phenotypically recessive against wildtype opaque skin (Z+). So a homozygous recesive can only be expressed in male. Translucent female Zod will be observed in presence of single alleli.

crosses with silkworms:

A. A translucent male crossed with a wildtype female.

a.The parental genotypes for this cross is Zod/Zod XZod/W

b.Punnett square and list of the expected phenotypic ratios.

Phenotypically opaque male and translucent female in 1:1 ratio will be produced
B. A homozygous wildtype male crossed with a translucent female.

a.The parental genotypes for this cross is: Z+/Z+ X Zod/W

b.Drawing of the Punnett square and list of the expected phenotypic ratios.

Expected phenotypic ratios Opaque male: opaque female in 1:1 ratio

C. A heterozygous wildtype male crossed with a translucent female

a. Parental genotype: Z+/Z+ X Zod/W

b. Punnett square and expected phenotypic ratios

expected phenotypic ratios Opaque male: translucent male: Opaque female: translucent female: 1:1:1:1

Z+ W Zod Zod/Z+ Zod/W Zod Zod/Z+ Zod/W

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