Question

in the cross bb x bb (two heterozygous mice), what percentage of the offspring would you predict to have the same phenotype as the parents? 0% 25% 50% 75% 100%

Explanation:

Step1: Set up Punnett - square

The cross is Bb x Bb. The possible gametes from each parent are B and b. The Punnett - square will have 4 cells: BB, Bb, bB, bb.

Step2: Determine phenotypes

Assume B is dominant for a certain phenotype (e.g., black fur) and b is recessive (e.g., white fur). Parents with Bb genotype have the dominant phenotype. Genotypes BB, Bb, and bB all show the dominant phenotype (because of the presence of the dominant allele B), while bb shows the recessive phenotype.

Step3: Calculate percentage

Out of 4 possible genotypes (BB, Bb, bB, bb), 3 genotypes (BB, Bb, bB) have the same phenotype as the parents (dominant phenotype). The percentage is $\frac{3}{4}\times100\% = 75\%$.

Answer:

75%