Question

what results from the fertilization of a gamete with an extra chromosome?
monosomy
aneuploidy
tetrasomy
trisomy

Explanation:

• Monosomy is the absence of one chromosome (having one copy instead of two), so it's not from an extra chromosome.
• Aneuploidy is a general term for abnormal chromosome number (gain or loss), but the specific result of a gamete with an extra chromosome fertilizing (leading to three copies of a chromosome) is trisomy. However, wait—actually, when a gamete with an extra chromosome (n+1) fuses with a normal gamete (n), the zygote has 2n+1, which is trisomy. But aneuploidy includes trisomy, monosomy, etc. Wait, no—let's recheck: The question is what results from fertilization of a gamete with an extra chromosome. A gamete with an extra chromosome (so its chromosome number is n+1, where n is the haploid number) when fertilized by a normal gamete (n) gives a zygote with 2n+1, which is trisomy (three copies of that chromosome). But aneuploidy is the broader category, but the specific result here is trisomy? Wait, no—wait, the options: Let's define each:
• Monosomy: 2n - 1 (missing one chromosome).
• Aneuploidy: Any abnormal number of chromosomes (gain or loss).
• Tetrasomy: 2n + 2 (four copies of a chromosome, from a gamete with n+2 fertilizing n).
• Trisomy: 2n + 1 (three copies of a chromosome, from a gamete with n+1 fertilizing n).

So when a gamete with an extra chromosome (n+1) is fertilized by a normal gamete (n), the zygote has 2n+1, which is trisomy. But wait, aneuploidy is the general term, but the question is "what results"—the direct result is trisomy? Wait, no—wait, maybe I made a mistake. Wait, the gamete has an extra chromosome (so it's n+1), and the other gamete is n. So the zygote is (n+1) + n = 2n + 1, which is trisomy. So the correct answer is trisomy? Or is aneuploidy correct? Wait, no—aneuploidy is the condition of having an abnormal number of chromosomes, so trisomy is a type of aneuploidy. But the question is asking what results from that fertilization. Let's check the options again. The key is: the gamete has an extra chromosome (so it's not missing, so not monosomy). Tetrasomy would be if the gamete had two extra chromosomes (n+2), so that's not it. Aneuploidy is a category, but trisomy is the specific result here. Wait, but maybe the answer is aneuploidy? No, because trisomy is a specific aneuploidy. Wait, let's re-express:

• If a gamete with an extra chromosome (n+1) fuses with a normal gamete (n), the zygote has 2n + 1, which is trisomy (three copies of one chromosome). So the result is trisomy. Wait, but let's confirm the definitions:

Trisomy: Presence of three copies of a chromosome (2n + 1).

Aneuploidy: Abnormal number of chromosomes (either extra or missing).

So the fertilization of a gamete with an extra chromosome (n+1) and a normal gamete (n) produces a zygote with 2n + 1, which is trisomy. So the correct option is trisomy (the fourth option). Wait, but maybe the answer is aneuploidy? No, because aneuploidy is the broader term, but the question is asking what the result is. Let's check the options again. The options are monosomy, aneuploidy, tetrasomy, trisomy.

So the correct answer is trisomy (the last option), because the zygote will have three copies of that chromosome (trisomy), which is a type of aneuploidy, but the specific result here is trisomy. Wait, but maybe I'm wrong. Wait, let's think again: the gamete has an extra chromosome (so it's n+1), and the other is n. So total is 2n + 1, which is trisomy. So the answer is trisomy (the option "trisomy").

Answer:

D. trisomy (assuming the options are labeled as A. monosomy, B. aneuploidy, C. tetrasomy, D. trisomy; if the original options are in order, the fourth option is trisomy)