Discussion
Which of the following chromosomal aberration results in formation of dicentric and acentric chromosomes ?
Answer: A
The aberration is a paracentric inversion.
In a paracentric inversion the inverted segment does not include the centromere. In a heterozygote the chromosomes pair by forming an inversion loop, and a single crossover inside the loop produces one chromatid with two centromeres (dicentric) and one with none (acentric). At anaphase I the dicentric forms a bridge that breaks, and the acentric fragment is lost.
A crossover in a pericentric inversion, which includes the centromere, gives chromatids with duplications and deletions but each with one centromere. Reciprocal translocations and simple deletions do not routinely give this dicentric and acentric pair.
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