Question

__________ can occur in either the first or second meiotic division to produce abnormal gametes. Choose the correct word from the below-given option to fill in the gap.

• A. Translocation
• B. Inversion
• C. Non-disjunction
• D. Insertions

Hint:

To determine when non-disjunction occurred:
- Non-disjunction in Meiosis I produces gametes carrying both maternal and paternal homologous chromosomes.
- Non-disjunction in Meiosis II produces gametes carrying identical sister chromatid copies from one parent.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Meiosis is a two-step cell division process (Meiosis I and Meiosis II) that produces haploid gametes (\(n\)) from a diploid cell (\(2n\)).
Proper gamete formation requires homologous chromosomes to separate in Meiosis I, and sister chromatids to separate in Meiosis II.

Step 3: Detailed Explanation:
Let us analyze the terms provided in the options:
Non-disjunction is the failure of chromosomes or sister chromatids to separate correctly during cell division.
- If non-disjunction occurs in Meiosis I, homologous chromosomes fail to separate.
Both chromosomes move to the same pole, producing gametes with an extra chromosome (\(n+1\)) or a missing chromosome (\(n-1\)).
- If non-disjunction occurs in Meiosis II, sister chromatids fail to separate.
This results in two normal gametes (\(n\)), one gamete with an extra chromosome (\(n+1\)), and one missing a chromosome (\(n-1\)).
Both types of non-disjunction produce aneuploid gametes, which can cause genetic disorders (such as Down syndrome) after fertilization.
Let us evaluate the other options:
Translocation and Inversion are structural changes where segments of chromosomes are rearranged or inverted.
They are not failures of chromosome separation during division.
Insertions are gene-level mutations where extra nucleotide base pairs are added to a DNA sequence.
Therefore, the process described is non-disjunction.

Step 4: Final Answer:
The phenomenon of failed chromosome separation in Meiosis I or II is non-disjunction, matching Option (C).