In an organism, pink spot is a sex-linked recessive trait and black hair heterozygous female is mated to a white male which is not spotted, the phenotypic ratio of the offspring would be

(1) 1/4 spotted black; 1/4 pink spotted white; 1/4 unspotted black; 1/4 unspotted white
(2) 1/2 pink spotted black; 1/2 pink spotted white
(3) 3/4 pink spotted black; 1/4 pink spotted white
(4) 3/4 unspotted black; 1/4 pink spotted white

Asked by Atulcaald | 19th May, 2018, 01:41: AM

Expert Answer:

Pink spot is a sex-linked recessive trait, which means that the trait is expressed only if it is present in homozygous condition.

Let allele B denote black colour and r denote pink spot.

Pink spotted black hair heterozygous female = Bbrr

Not spotted white hair male = bbRr

Parents:    Bbrr         x      bbRr

Gametes: Br, br                bR, br

 

bR

br

Br

BbRr

black unspotted

Bbrr

Black pink spotted

br

bbRr

white unspotted

bbrr

white pink spotted


This implies that the phenotypic ratio of the offspring produced are-

¼ black unspotted : ¼ Black pink spotted : ¼ white unspotted : ¼ white pink spotted.

Answered by Sheetal Kolte | 21st May, 2018, 10:38: AM