12. Following is the picture of an inversion heterozygote undergoing a single crossing – over event

The following statements are given towards explaining the consequences at the end of meiosis.
A. The resultant two chromosomes will have deletions and duplications.
B. A dicentric and an acentric chromosome will be formed.
C. The inversion does not allow crossing over to occur, so even if a crossing over is initiated, it will fail to occur.
D. The crossing over is considered suppressed by inversion as the acentric chromosome will not segregate normally.
E. All the gametes formed with cross-over chromatid at the end of meiosis will be non-viable as they carry large deletion or duplication.
F. The gametes having non-crossover (parental) chromatid will survive.
Which combination of statements is correct?
(1) B and E            (2) A and C
(3) B, D, and F       (4) A, E and F

Understanding the diagram

The figure shows an inversion heterozygote (one normal and one inverted homolog) with a single crossover within the inversion loop. This is a classic paracentric inversion (centromere outside the loop).

Consequences:

• Two chromatids remain non‑recombinant (one normal sequence, one inverted).

• Two recombinant chromatids are:

  • Dicentric (two centromeres) with deletions/duplications.

  • Acentric (no centromere) with deletions/duplications.

• During anaphase, the dicentric forms a bridge and breaks; the acentric is lost.

• Thus, gametes carrying crossover chromatids are non‑viable; only non‑crossover (parental) chromatids give functional gametes.

Evaluating each statement

A. “The resultant two chromosomes will have deletions and duplications.” – Incorrect

• Only the recombinant chromatids (two of the four) have deletions/duplications; the two parental chromatids remain structurally normal.

B. “A dicentric and an acentric chromosome will be formed.” – Correct

• This is the hallmark of a single crossover in a paracentric inversion loop.

C. “The inversion does not allow crossing over to occur, so even if a crossing over is initiated, it will fail to occur.” – Incorrect

• Crossing over does occur; it is the products that are inviable, not the crossing over process itself.

D. “The crossing over is considered suppressed by inversion as the acentric chromosome will not segregate normally.” – Correct

• The acentric fragment is lost and the dicentric breaks; thus recombinant gametes are not recovered, giving an apparent suppression of crossing over.

E. “All the gametes formed with cross‑over chromatid at the end of meiosis will be non‑viable as they carry large deletion or duplication.” – Correct in content, but note that the options ask for combinations; E describes the same consequence as D and F, but the key combination provided with E does not include B and D together.

F. “The gametes having non‑crossover (parental) chromatid will survive.” – Correct

• Only gametes that receive normal or purely inverted parental chromatids (no deletions/duplications) are viable.

Given the answer choices, the set that correctly captures the essential consequences—dicentric and acentric formation, suppression of recombinants, and survival of only parental chromatids—is B, D and F → option (3).