What term describes the failure of homologous chromosomes (or chromatids) to separate properly during meiosis, potentially producing gametes missing a chromosome or with an extra copy?

What term describes the failure of homologous chromosomes (or chromatids) to separate properly during meiosis, potentially producing gametes missing a chromosome or with an extra copy?

• A. Zygote
• B. Crossing over
• C. Recombination
• D. Nondisjunction error

Answer: (C)

Nondisjunction is the process at play here. It describes when homologous chromosomes or sister chromatids fail to separate during meiosis, so some gametes end up with too few or too many chromosomes. If nondisjunction happens in meiosis I, all gametes can have an abnormal chromosome number; if it happens in meiosis II, only some gametes are affected. When such a gamete fuses with a normal gamete, the resulting zygote can be monosomic (missing a chromosome) or trisomic (an extra chromosome). Crossing over and recombination are normal exchange events that shuffle genetic material and are not about chromosome separation, while a zygote is simply the fertilized cell that results after union of gametes.

Nondisjunction is the process at play here. It describes when homologous chromosomes or sister chromatids fail to separate during meiosis, so some gametes end up with too few or too many chromosomes. If nondisjunction happens in meiosis I, all gametes can have an abnormal chromosome number; if it happens in meiosis II, only some gametes are affected. When such a gamete fuses with a normal gamete, the resulting zygote can be monosomic (missing a chromosome) or trisomic (an extra chromosome). Crossing over and recombination are normal exchange events that shuffle genetic material and are not about chromosome separation, while a zygote is simply the fertilized cell that results after union of gametes.