8. The structural change which leads into crossover suppression and position effect is
(1) Deletion             (2) Duplication
(3) Inversion          (4) Translocation

Concept: why inversions fit both features

A chromosomal inversion occurs when a segment between two breaks is reinserted in the reverse orientation.

• In inversion heterozygotes, homologous chromosomes must form an inversion loop to pair. Crossovers inside this loop often generate unbalanced gametes (with deletions/duplications), so such recombinant chromatids are eliminated. Functionally this appears as crossover suppression within the inverted region.

• Inversions change gene position along the chromosome. If a gene is moved near heterochromatin or different regulatory domains, its expression can change even though its coding sequence is intact—this is a classic position effect.

Therefore, only inversion simultaneously explains crossover suppression and position effect.

Option‑wise explanation

1. Deletion

   • Removes a chromosome segment. It changes gene dosage and can unmask recessive alleles, but the region is simply gone; recombination there cannot be “suppressed” in the same mechanistic sense, and position effects are not the hallmark feature.

2. Duplication

   • Produces extra copies of a segment, altering gene dosage. While it can affect pairing and sometimes recombination, it is not typically described as causing systematic crossover suppression and classical position-effect variegation.

3. Inversion – correct

   • Balanced rearrangement (no net gain/loss of DNA).

   • Crossover suppression inside the inversion loop in heterozygotes.

   • Position effect because gene order and chromosomal neighborhood change.

4. Translocation

   • Exchanges segments between non‑homologous chromosomes. This can cause semi-sterility or position effects at breakpoints, but the classic, textbook association of both crossover suppression within a defined segment plus position effects is strongest for inversions.

Hence, the structural change that leads to both crossover suppression and position effect is chromosomal inversion (option 3).