Question

7. During a genetics simulation, students calculate that each parent can produce 8 different gametes. When they consider the possible combinations, they realize that 64 unique zygotes could result from the pairing of sperm and egg. One group concludes that this is why siblings can have very different genotypes, even though they have the same parents. Another group is unsure and suggests that gametes pair in a predictable order, so fertilization doesn’t really matter.

What best explains the siblings’ genetic differences in this case?

Responses

A. Meiosis ensures all gametes are genetically identical, so fertilization doesn’t affect variation.
A. Meiosis ensures all gametes are genetically identical, so fertilization doesn’t affect variation.

B. Independent assortment occurs only during fertilization, not during gamete formation.
B. Independent assortment occurs only during fertilization, not during gamete formation.

C. Mutations after birth explain why siblings differ in their genes.
C. Mutations after birth explain why siblings differ in their genes.

D. Fertilization is random, so any sperm can unite with any egg, creating many possible combinations.
D. Fertilization is random, so any sperm can unite with any egg, creating many possible combinations.

E. Gametes always combine in a set order, so environment must explain sibling differences.

Answer 1

D. Fertilization is random, so any sperm can unite with any egg, creating many possible combinations.

Explanation: Meiosis (with independent assortment and crossing over) generates genetically different gametes, and fertilization is essentially random — any sperm can fuse with any egg — producing the many possible zygotes (8 × 8 = 64). The other choices are incorrect: meiosis does not make identical gametes; independent assortment happens during gamete formation (meiosis), not at fertilization; post‑birth mutations affect somatic cells and don't explain inherited genotype differences between siblings; and gametes do not combine in a fixed order.