Question

Cross between homozygous black rough (BBRR) guinea pig and homozgous white smooth guinea pig (bbrr) produced black and rough animals in F${}_1$ generation. Presuming the genes to be present on different chromosomes, the percentage of F${}_2$ individuals which are heterozygous for both the gene pairs would be

• A. 25%
• B. 35%
• C. 50%
• D. 75%

Answer 1

The correct option is A 25%

Due to presence of both genes on different chromosomes, the genes follow independent assortment and do not show linkage.

Parent generation (P${}_1$) : BBRR x bbrr

F${}_1$ generation BbRr

Selfing of F${}_1$ generation : BbRr x BbRr

Gametes BbRr---> BbRr	BR	Br	bR	br
BR	BBRR	BBRr	BbRR	BbRr
Br	BBRr	BBrr	BbRr	Bbrr
bR	BbRR	BbRr	bbRR	bbRr
br	BbRr	Bbrr	bbRr	bbrr

Thus, proportion of F${}_2$ individuals which are heterozygous for both gene pairs (BbRr) = 4/16 = 1/4 or 25%. Correct option is A.