Look at the Punnett square obtained by the monohybrid cross between two rabbits.

Question

B b
B BB Bb
b Bb bb

Here, B represents the allele for black hair and b represents the allele for white hair. If both the rabbits crossed had genotype Bb, what will be the phenotypic ratio for the observable monohybrid crosses (complete dominance)?


Responses
A 1:1:1:11:1:1:1
B 2:22:2
C 2:1:12:1:1
D 3:1

Answer 1

In a monohybrid cross between two rabbits with the genotype Bb (heterozygous for black hair), the Punnett square shows the following genotypes:

• BB (homozygous dominant) - Black hair
• Bb (heterozygous) - Black hair
• Bb (heterozygous) - Black hair
• bb (homozygous recessive) - White hair

The resulting genotypic ratio is:

• 1 BB: 2 Bb: 1 bb.

For the phenotypes, the black hair (both BB and Bb) is dominant over the white hair (bb). Therefore, the phenotypic ratios are:

• 3 black hair (BB + Bb) to 1 white hair (bb).

This gives a phenotypic ratio of:

• 3 (black hair) : 1 (white hair).

So, the correct response is:

D) 3:1.