16. When gamete formation occurs in individuals heterozygous for an inversion, some of the following possibilities may occur:
A. A pericentric inversion heterozygote results in an acentric and a dicentric chromosome at the end of meiosis I
B. A paracentric inversion heterozygote also results in an acentric and a dicentric chromosome at the end of meiosis I
C. 25% of gametes formed in inversion heterozygoteare non-viable
D. Inversion are considered as cross-over suppressors because the gametes having a cross over product do not survive
Which combination of the above statements is correct to explain the meiotic consequence in inversion heterozygote?
(1) A and D           (2) B and C
(3) A and B           (4) B and D

Quick recap: inversions and meiosis

• Paracentric inversion: inverted segment does not include centromere.

• Pericentric inversion: inverted segment includes centromere.

• In an inversion heterozygote, homologous chromosomes form an inversion loop during pairing.

• A single crossover inside this loop creates abnormal recombinant chromatids that usually produce non‑viable gametes.

Evaluation of each statement

A. Pericentric inversion → acentric and dicentric chromosomes – Incorrect

• In pericentric inversion heterozygotes, crossover inside the loop produces recombinant chromatids each with one centromere, but with segmental duplication and deletion.

• Acentric and dicentric chromatids are characteristic of paracentric, not pericentric, inversions.

B. Paracentric inversion → acentric and dicentric chromosomes – Correct

• In a paracentric inversion heterozygote, a crossover within the loop yields:

  • One dicentric chromatid (two centromeres).

  • One acentric fragment (no centromere).

• These cannot segregate normally at anaphase I and lead to non‑viable gametes.

C. “25% of gametes formed in inversion heterozygote are non‑viable” – Incorrect/generalized

• With a single crossover in one chromatid pair, two of four chromatids (50%) are recombinant and typically unbalanced, so up to 50% of gametes may be non‑viable.

• The actual fraction can vary with crossover frequency; a rigid 25% is not a general rule.

D. Inversions act as cross‑over suppressors because crossover products do not survive – Correct

• Pairing and crossing over do occur, but recombinant chromatids (acentric/dicentric or deletion/duplication) usually lead to inviable gametes.

• Only non‑crossover parental chromatids contribute to the next generation, so recombination is effectively “suppressed” within the inverted region.

Final answer

The statements that correctly explain meiotic consequences in inversion heterozygotes are:

• B. A paracentric inversion heterozygote also results in an acentric and a dicentric chromosome at the end of meiosis I.

• D. Inversions are considered cross‑over suppressors because the gametes having a cross‑over product do not survive.

So the correct option is (4) B and D.