Question

Zebra Mussel Genetics
Zebra mussels are originally native to Russia. In the mid-1980s, zebra mussels were introduced into the Great Lakes region of the United States where they rapidly reproduced. Females can produce up to one million eggs per year. In one zebra mussel population, most of the individuals have dark, zebra-striped shells (genotype AA). However, solid light-colored shells (genotype aa) occur in 1 of every 10,000 individuals. The solid light-colored shells indicate mussels that are not hardy in cold water temperatures (<
C). Heterozygous individuals (Aa) have solid, dark-colored shells.
If you cross a mussel with dark, zebra-striped shells with a mussel with solid light-colored shells, how many offspring would you expect to have the have solid, dark-colored shells?
A 0%
B 50%
C 75%
D 100%
Which cross would produce the greatest genetic diversity among the offspring?
A AA x aa
B AA x Aa
C aa x Aa
D Aa x Aa

Answer 1

Question 1:
Cross: AA (dark, zebra-striped) × aa (solid light)
All offspring will be Aa, and Aa = solid, dark-colored shells.
Answer: D — 100%

Question 2:
Compare genotype outcomes:
- AA × aa → 100% Aa (1 genotype)
- AA × Aa → 50% AA, 50% Aa (2 genotypes)
- aa × Aa → 50% aa, 50% Aa (2 genotypes)
- Aa × Aa → 25% AA, 50% Aa, 25% aa (3 genotypes)

Greatest genetic diversity: D — Aa × Aa.