3. Chromosome aberration characterized by lack of crossing over, pseudo-dominance and non-reversal of mutation occurs in-
(1) Inversion               (2) Deletion
(3) Translocation       (4) Duplication

Why deletion fits the description

In a chromosome with a deletion:

• The corresponding region is absent, so during meiosis the intact homolog forms a loop; no normal crossing over can occur inside the deleted segment because there is no partner sequence.

• If the deleted region carried a dominant allele (A) and the normal homolog carries recessive a, loss of A leaves only a in single copy; the recessive phenotype appears in a heterozygote, a phenomenon called pseudo‑dominance.

• Since a whole DNA segment is physically lost, the chromosome cannot “revert” back to the original normal structure by a simple back‑mutation; hence “non‑reversal of mutation”.

Therefore, the aberration described is deletion.

Why the other options are incorrect

1. Inversion

• The segment is reversed but not lost. Crossing over in the inversion loop is reduced or produces unbalanced gametes, but the genes are still present and some recombination can occur; it does not characteristically cause pseudo‑dominance or irreversibility by loss of DNA.

3. Translocation

• Segments are exchanged between non‑homologous chromosomes. Crossing over is altered but not absent; pseudo‑dominance is not a hallmark, because gene loss is not inherent.

4. Duplication

• A segment is present in extra copies. Crossing over can still occur; instead of loss, there is additional DNA. This does not create pseudo‑dominance or irreversible loss‑of‑function through deficiency.

Hence, the chromosome aberration with lack of crossing over in the missing region, pseudo‑dominance, and non‑reversal is (2) Deletion.