Question

In structural chromosome mutations pericentric inversion mutation means

• A. A portion in the chromosome is reversed and gets inserted back into the other arm of the same chromosome
• B. Some part of the chromosome is deleted and new is added
• C. A portion in the chromosome is reversed and gets inserted back into the same arm of the chromosome
• D. A portion in the chromosome is reversed and gets inserted back into the other chromosome

Hint:

• Inversion A chromosomal segment is detached, rotated 180 degrees, and reinserted.
• Paracentric Inversion Does NOT include the centromere. Breaks are in one arm.
• Pericentric Inversion DOES include the centromere. Breaks are in different arms (one on each side of the centromere). Can change arm length ratio.

Answer 1

The Correct Option is A

Chromosomal inversions are structural mutations where a segment of a chromosome breaks off, rotates 180 degrees, and then reattaches to the same chromosome. There are two main types of inversions based on whether the inverted segment includes the centromere: 1. Paracentric Inversion: The inverted segment does not include the centromere. Both breaks occur in the same arm of the chromosome. 2. Pericentric Inversion: The inverted segment does include the centromere. The breaks occur in different arms of the chromosome (one in the short arm 'p', one in the long arm 'q'). A pericentric inversion can change the relative lengths of the chromosome arms and thus potentially alter the chromosome's morphology (e.g., from metacentric to submetacentric). Let's analyze the options: (a) "A portion in the chromosome is reversed and gets inserted back into the other arm of the same chromosome": This phrasing is a bit imprecise. For a pericentric inversion, the segment that includes the centromere is reversed. If the breaks are on opposite sides of the centromere, then parts of "other" arms are involved in the inverted segment. This is the closest description to a pericentric inversion if "inserted back into the other arm" means the inverted segment now spans parts of what were originally different configurations of the arms relative to the centromere, or that arm lengths change. More accurately, the inverted segment *includes* the centromere. (b) "Some part of the chromosome is deleted and new is added": This describes deletion and insertion, not inversion. (c) "A portion in the chromosome is reversed and gets inserted back into the same arm of the chromosome": This describes a paracentric inversion (centromere not included). (d) "A portion in the chromosome is reversed and gets inserted back into the other chromosome": This describes a translocation, not an inversion on the same chromosome. Given the options, option (a) is the most plausible description intended for a pericentric inversion, focusing on the involvement of both arms (implicitly because the centromere is included in the inversion). A key feature of pericentric inversion is that the inverted segment contains the centromere. If the break points are in different arms, then the orientation of the segment containing the centromere is flipped, affecting how the arms are now constituted. The phrasing could be better, e.g., "An inversion that includes the centromere." But (a) implies the centromere is involved. \[ \boxed{\parbox{0.9\textwidth}{\centering A portion in the chromosome is reversed and gets inserted back into the other arm of the same chromosome (implying the centromere is within the inverted segment)}} \]