Question

a brown mouse is repeatedly crossed with a white mouse and produces 43 offspring, all of which are brown. assuming that mouse hair color is a mendelian trait (dominant allele = b), drag the correct genotype to each parent mouse.
bb bb bb
brown mouse
white mouse

Explanation:

Step1: Recall Mendelian genetics rules

In Mendelian traits, a dominant allele (B) masks a recessive allele (b). Brown is dominant (B -) and white is recessive (bb).

Step2: Analyze the offspring

Since all 43 offspring are brown, the white - colored parent must be homozygous recessive (bb) to contribute a recessive allele. The brown - colored parent must be homozygous dominant (BB) so that all offspring get a dominant B allele and express the brown phenotype.

Answer:

Brown mouse: BB
White mouse: bb