Question

What is criss-cross inheritance? Explain with suitable example.

Answer 1

Criss-cross inheritance is the type of inheritance in which the genes are passed on from father to daughter and then to her son, i.e. from male to female and from female to male (grandson). In other words, it is also said that the transmission is from the grandfather to his grandson through his daughter

I. Inheritance of Colour blindness show crisscross pattern. 

(1) Colour blindness is a sex-linked disorder in which the person concerned cannot distinguish between red and green colours. 

(2) It is recessively X-linked disorder, which is expressed in males. It is rarely seen in females. 

(3) The genes for normal vision are dominant whereas those for colour blindness are recessive.

(4) 

Gene for normal vision : X^c

Gene for colour blindness : X^c

Normal female : X^cX^c 

Normal male : X^c Y 

Colour blind female : X^c X^c

Carrier female : X^c X^c 

Colour blind male : X^c Y

II. Crosses showing the inheritance of colour blindness: 

(i) A cross between normal female and colour blind male.

(ii) A cross of carrier female with normal male.

(1) Normal female with Colour blind male. Such cross produces 50% carrier daughters and 50% normal sons.

(2) Carrier female with normal male. Such a cross produces 25% normal daughters, 25% normal sons, 25% carrier daughters and 25% colour blind sons.

(3) Colour blind father transmits the disorder to his grandson through his carrier daughter. The inheritance of characters from the father to his grandson through his daughter is called criss-cross inheritance.