Q.Father of a child is colourblind and mother is carrier for colourblindness, the probability of the child being colourblind is

Step 1. Write the parental genotypes: colourblind father = XcY (hemizygous recessive); carrier mother = XCXc (heterozygous, normal vision but carrying the recessive allele).

Step 2. List the gametes: father gives Xc or Y; mother gives XC or Xc.

Step 3. Cross all four combinations: XC(mother) x Xc(father) → XCXc, carrier daughter, normal vision; Xc(mother) x Xc(father) → XcXc, colourblind daughter; XC(mother) x Y(father) → XCY, normal son; Xc(mother) x Y(father) → XcY, colourblind son. …

Punnett-square XcY (father) x XCXc (mother) and count the fraction of the four off …

• Only checking sons for colourblindness and forgetting that a carrier mother can also produce a colourblind (XcXc) daughter when the father is colourblind. …