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 condition. Males receive their X chromosome from their mother; females receive one X from each parent. A daughter inherits the affected Xc chromosome from her father and a normal XC from her mother, becoming a carrier. A son cannot inherit Xc from his father because he receives only the Y chromosome. Cross:

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

- Consequently, neither the son nor the daughter can inherit colour blindness from the father due to its X-linked nature.