Question

If a human sperm with the normal number of chromosomes fertilizes a human

egg with one extra chromosome # 21, how many chromosomes would the zygote
have?
47 total

24 total

22 total

45 total

Answer 1

47 total

Step-by-step explanation:

Since both sperm and egg cells are diploid, they only have 23 chromosomes instead of 23 PAIRS (46 total). When they merge and create a zygote, the resulting cell has a complete 23 pairs, or 46 chromosomes. However, if a human egg has an extra #21, then it has 24 chromosomes, and the resulting zygote has 23+24=47 total chromosomes. This is trisomy 21, or what is widely called Down Syndrome.