Question

Differentiate between Paracentric inversion and Pericentric inversion.

Answer 1

Hint: Pericentric and paracentric terms are used with reference to the presence or absence of centromere in the inverted chromosomal segment.

Complete Answer:
An inversion is produced when there are two breaks in a chromosome and the intercalary segment rotates at 180° and reunites in reverse order. The inversions are of two types – (i) paracentric inversion, and (ii) pericentric inversion. The differences between these two types of inversions are –

Sl.No	Paracentric inversion	Pericentric inversion
1.	In this type of inversion, the inverted segment does not include centromere.	In this type of inversion, the inverted segment includes centromere.
2.	In paracentric inversion, a single crossing over an inverted region results in the formation of a dicentric chromosome (a chromosome having two centromeres) and an acentric (a chromosome without centromere) chromosome.	In pericentric inversion, a single crossing over in an inverted region results in deficiencies and duplications after meiosis. In this type of inversion, dicentric bridges or acentric fragments are not formed.
3.	During meiosis at Anaphase I the dicentric chromatid and acentric chromatid appear as a dicentric bridge and a fragment.	In this type of inversion, if the breaks in chromosomes are not present at equal distance from centromere, this results into change in the shape of the chromosome eg. From metacentric to sub-metacentric or vice versa.

Note: Apart from these two types there is another type of inversion called as overlapping inversions. When in a chromosome already having one inversion, a second inversion is induced and the inverted segments involved in first and second inversions have a common region, then it is referred to as an overlapping inversion.