Question

Assume non-disjunction occurs in meiosis II in oogenesis. If the resulting gametes are fertilized by normal sperm, what types of zygotes can be produced?

1) Zygotes with normal chromosome number
2) Zygotes with abnormal chromosome number
3) Zygotes with extra chromosomes
4) Zygotes with missing chromosomes

Answer 1

Nondisjunction in meiosis II during oogenesis can result in zygotes with normal, abnormal, or an extra or missing chromosome when these gametes are fertilized by normal sperm. This can lead to conditions like Down Syndrome.

Step-by-step explanation:

When nondisjunction occurs in meiosis II during oogenesis, and the resulting gametes are fertilized by normal sperm, four potential zygote outcomes are possible:

• Zygotes with a normal chromosome number (n).
• Zygotes with an abnormal chromosome number.
• Zygotes with an extra chromosome (trisomy).
• Zygotes with a missing chromosome (monosomy).

Although nondisjunction in meiosis II typically leads to two normal gametes and two abnormal ones, the zygotes formed after fertilization with normal sperm could have either the correct number of chromosomes, a missing chromosome, or an extra chromosome. These conditions can lead to various developmental and health issues, with Down Syndrome being one example of a trisomy condition.