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4. In humans, red-green color blindness is recessive to normal sight. The gene for this trait is...

4. In humans, red-green color blindness is recessive to normal sight. The gene for this trait is carried on the X chromosome. In each of the following, give the genotype and phenotype of all possible offspring and their expected ratios. Give the phenotypic ratios of males ♂ and females ♀ separately (ALWAYS FOR X-LINKAGE):

(a) a color-blind man married to a normal- sighted woman whose father is color-blind;

(b) a man with normal color vision married to a color-blind woman.

Solutions

Expert Solution

4) let the alleles be XC- normal Xc- colourblind ( recessive)

males who carry the mutated allele in their X chromosome is colourblind and for females to be colourblind both of their X chromosomes has to have recessive alleles.

a) genotype of the colour blind man is XcY and genotype of the normal- sighted woman whose father is color-blind is XCXc ( she has inherited Xc allele from her father since she has normal vision she has XC allele)

so XCXc * XcY

	XC	Xc
Xc	XCXc ( female with normal vision)	XcXc (colorblind female)
Y	XCY ( male with normal vision)	XcY (colorblind male)

genotypes and phenotypes of the progenies are given in the punnet square

genotypic ratio in males is

XCY: XcY=1:1

Genotypic ratio in females is

XCXc:XcXc=1:1

phenotypic ratio in males

normal vision: colourblind=1:1

phenotypic ratio in females

normal vision: colourblind=1:1

b) genotype of man with normal vision XCY and genotype of the woman with colorblindness is XcXc

XCY * XcXc

	XC	Y
Xc	XCXc ( female with normal vision)	XcY (colorblind man)
Xc	XCXc ( female with normal vision)	XcY (colorblind man)

genotypic ratio in males is

XCY: XcY=0:1

Genotypic ratio in females is

XCXc:XcXc=1:0

phenotypic ratio in males

normal vision: colourblind=0:1

phenotypic ratio in females

normal vision: colourblind=1:0

gladiator answered 1 year ago

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