7) Color Blindness is a sex chromosome linked trait. A woman with normal vision,

Question

7) Color Blindness is a sex chromosome linked trait. A woman with normal vision, whose father was color has a child with a man with normal vision Color Vision alleles: Xc= normal color vision allele, xc=color blindness allele Genotype xcxc xcY Phenotype Normal female Normal female -carrier for color blind allele Color blind female Normal male Color blind male XcY What are the genotypes of the woman and man? What proportion of their sons are expected to be color blind? Note: This question is only in regards to the sons. Do not include the daughters in your calculations What proportion of their daughters are exp the daughters. Do not include the sons in your calculations. a) b) ected to be carriers? Note: This question is only in regords c)

Explanation / Answer

7. a. Color blindness is a sex chromosome linked trait.

Given, the woman has normal vision but her father was color blind which means her father has XcY genotype. The woman acquires one X chromosome from her father. Since she has normal vision her genotype will thus be XCXc. The woman is therefore a carrier of the disease.

The man has a normal vision. So, his genotype will be XCY.

Therefore, the genotype of woman is XCXc and genotype of male is XCY.

Punnett square for the cross between woman who is carrier for the disease and a man with normal vision is as follows:

XC

Y

XC

XCXC

XCY

Xc

XCXc

XcY

b. As per the Punnett square, the proportion of their sons who are expected to be color blind (XcY ) is ½ = 0.5.

c. As per the Punnett square, the proportion of their daughters who are expected to be carriers (XCXc ) is ½ = 0.5

XC

Y

XC

XCXC

XCY

Xc

XCXc

XcY

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