Question

When does nondisjunction occur which affects inheritance?

Answer 1

Answer:

The correct answer would be meiosis.

Nondisjunction refers to the failure of separation of one or more homologous chromosome pairs or that of sister chromatids during nuclear division.

It can occur in both meiosis as well as mitosis, however, meiosis (formation of gametes) is involved in inheritance, so, the correct answer would be meiosis.

During anaphase I, nondisjunction occurs when homologous chromosome pair(s) fails to separate. In anaphase II, it occurs due to the failure of separation of sister chromatids.  

It results in the formation of gametes with abnormal chromosome number.

Answer 2

The answer is the first one, meiosis. This nondisjunction could occur whether in meiosis I or meiosis II. For example, an autosomal nondisconjunction at meiosis I can determine if the baby will be born with down syndrome.