Question

Suppose you collected a population of 50 mice from the wild that had a mixture of grey and yellow mice. Assuming fur color is genetically determined by a single gene, how could you go about determining which trait is dominant and which is recessive?

Answer 1

The answer to the question: How could you go about determining which trait is dominant and which is recessive, would be: Because the traits for yellow, or grey colored fur, which are present in a single gene, will be part of the chromosomic pairing that will happen when a chromosome from the father, and one from the mother combine.

As such, some of these traits will be present in chromosomic alleles as dominant and some as recessive. Since it is one single gene, we will assign it a letter (B). Now, some of the traits will be dominant (B), and some will be recessive (b). When these traits combine, there are three possibilities. One, that the resulting offspring obtains two homozygotic dominant alleles (BB), another is that the offspring receive a heterozygotic pairing (Bb) and the third that they receive another homozygotic but recessive pairing (bb).

Depending on which of the two colors express phenotypically for the dominant allele B, and which for the recessive b, you will have the incidence of the different colors in the population of 50 mice.

Answer 2

Step-by-step explanation:

Some of the mice will be homozygous dominant (AA), others will be heterozygous (Aa) and others homozygous recessive (aa).

Because the population isn't homogeneous, the easiest way would be to mate all grey mice on one side, and all yellow mice on the other, and analyze the phenotype of the offspring.

The cross between mice with the recessive trait will have 100% offpsring with the recessive trait.

• aa x aa ---> F1: aa

However, the cross between mice with the dominant trait will show some recessive individuals in the offspring:

• AA x AA ---> all A_
• AA x Aa ---> all A_
• Aa x Aa ---> 3/4 A_, 1/4 aa