Mice have two unlinked allele pairs that affect fur color. The table shows how allele pairs affect fur color. The term “agouti” describes fur with pigmentation that changes in each hair from the shaft to the tip, giving the fur a banded appearance. Mice with the aa allele pair are albino, regardless of the second allele-pair combination.

Question

What is the probability of albinism in the offspring of a cross between two mice with AaBb alleles?

Answer 1

To determine the probability of albinism in the offspring of a cross between two mice with the genotype AaBb, we need to analyze the inheritance of the alleles involved.

Allele Key:

• A (agouti): Dominant allele for fur color that produces pigmentation.
• a (albino): Recessive allele for albinism.
• B (also a fur color trait): Let's assume it is a dominant allele, but it does not affect albinism.
• b: The recessive allele that may have some effect on fur color but is not relevant for albinism.

Parental Genotypes:

Both parents are AaBb.

Step 1: Punnett Square for A and a

For the alleles A and a, the possible gametes from each parent are:

• From Parent 1: A, a
• From Parent 2: A, a

The Punnett square for these alleles is:

| | A | a | |------|-----|-----| | A | AA | Aa | | a | Aa | aa |

From this Punnett square, the offspring probabilities for the A and a alleles are:

• 25% AA (agouti)
• 50% Aa (agouti)
• 25% aa (albino)

Step 2: Calculate Probability of Albinism

From the cross Aa x Aa, the probability of an offspring being aa (albino) is 25% (or 1/4).

Since the albino trait is determined only by the presence of the aa genotype, the second allele pair (B and b) does not affect the probability of albinism.

Conclusion

The probability of albinism in the offspring of a cross between two mice with AaBb alleles is 25% or 1/4.