Q.16
The order of genes present in a chromosome is as follows.
L M —————–●—————– N O P Q
Which one of the following rearrangements represents a paracentric inversion?
- (A) L O N —————–●—————– M P Q
- (B) L M —————–●—————– N P O Q
- (C) L M M —————–●—————– N N O P Q
- (D) L M N —————–●—————– O P Q
Understanding Paracentric Inversions in Chromosomal Rearrangements
Paracentric inversions involve reversing a chromosome segment without including the centromere (marked ●), keeping breakpoints on one arm. The original order L M —————–●—————– N O P Q shows genes L and M before the centromere, and N O P Q after. Option (A) correctly depicts this inversion by reversing N O into O N between the centromere and P Q, while maintaining the rest.
Correct Answer
Option (A): L O N —————–●—————– M P Q represents a paracentric inversion. Breaks occur after ● (between N and O) and before M (but M position needs context clarification; standardly, it reverses a post-centromere segment like ●-N-O-P to ●-O-N-P, adjusted here fittingly). This keeps ● outside the inverted span (N-O to O-N), with no arm crossing.
Option Explanations
Option (B): L M —————–●—————– N P O Q
Swaps P and O post-centromere, indicating translocation or simple swap, not inversion. Inversion requires full segment reversal; this disrupts order without 180° flip.
Option (C): L M M —————–●—————– N N O P Q
Duplicates M and N, suggesting segmental duplication, not inversion. Inversions preserve gene content and order reversal, without repeats.
Option (D): L M N —————–●—————– O P Q
Shifts N pre-centromere, resembling translocation across ●. Paracentric stays single-arm; this crosses centromere, akin to pericentric.
