In: Biology
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.
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