3. In mice, black fur color is dominant to white When two heterozygous black rat

Question

3. In mice, black fur color is dominant to white When two heterozygous black rats are mated, what would be the probability of the following combination, of offspring? A. A litter of six pups, four with black fur and two with white fur. B. A litter of six pups, the firstborn with white fur, and among the remaining five pups, two with white fur and three with black fur C. A first litter of six pups, four with black fur and two with white fur, and then a second liner of seven pups, five with black fur and two with white fur. D. A first litter of five pups, four with black fur and one with white fur, and then a second liner of seven pups in which the first born is homozygous, the second born is black, and the remaining five pups are three black and two white.

Explanation / Answer

Black is B and White is b and heterozygous black rats are Bb and homozygous white rats are bb. Heterozygous Bb genotype produces phenotype intermediate to those produced by BB and bb
Cross between two Heterozygous (Bb) parents.

A cross between two heterozygous black fur animals (rats) will in the first filial generation yield Three(3) phenotypically black and one(1) white offspring in the ratio of 3:1.

Of the 3 phenotypically black fur animals, 2 will be heterozygous black and 1 homozygous black. The white offspring will be homozygous recessive.
The cross will be as follows-
Heterozygous Parents .....(Bb ) x ( Bb )
Genes segregate.............(B ) ( b ) x ( B ) ( b ) for crossing.

F1 offsprings.................... (BB), (Bb) , (Bb), (bb)
Phenotypic proportion......3 black fur: 1 white fur, Proportion = 3:1 or 75% tall, 25% short.

1Bb:2Bb:1bb for the genotypes, 3tall:1short for the phenotypes

Bb x Bb would produce the following genotypes/phenotypes:

1 BB (homozygous black)
2 Bb (heterozygous black)
1 bb (homozygous white)

25% dominant, 50%carrier, 25% recessive

1. Bb, Bb, Bb, Bb, - white pups ans bb, bb white pups.

2. first born bb, white pups - bb bb, Bb, Bb, BB

3. Bb, Bb, BB, BB,Bb, Bb black pups and bb, bb white pups, second litter BB, BB, Bb, Bb, Bb black pups, and bb, bb two white,

4. BB, bb, Bb, Bb, Black pups, bb white, second litter - Bb, second is Bb, and the rest BB, Bb,, bb- black and bb, bb- white

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