Question

In a family, the father, the daughter, and the son are colour blind, whereas the mother has normal vision. Do you think the son and daughter have inherited the disease from their father? Work out a cross to justify your answer.

Hint:

For X-linked inheritance: - Males inherit X-linked traits from mothers. - Fathers pass X-linked traits only to daughters.

Answer 1

Colour blindness is an X-linked recessive disorder. Males inherit the X chromosome from their mother, while females inherit one X chromosome from each parent. The daughter inherits the Xc chromosome from her father and XC (normal) from her mother, making her a carrier. The son cannot inherit Xc from the father as he receives only the Y chromosome from him. Cross:

 Father (XcY) ×Mother (XCXC) 
Gametes: Xc, Y (Father) and XC, XC (Mother) 
Offspring:Daughter (XCXc) (Carrier) 
Son (XCY) (Normal).

- Hence, the son and daughter cannot inherit colour blindness from the father as it is X-linked.