Question

1. A. Given the chromosome arrangement shown below, draw what this chromosome might look like with a pericentric inversion. The 'x' represents the centromere. (1 pt)

A B C D x E F G H I

B. Describe why being heterozygous for an inversion such as this might be detrimental. (1 pt)

C. Would you expect to see any evidence of a defect or phenotype in someone homozygous for an inversion? Why or why not? (1 pt)

Answer 1

1.A.Ans : With a pericentric inversion, the given chromosome would look like :

B.Ans : Inversion occurs when a part of the chromosome detaches, flips over (180 turn) and reattaches with the chromosome such that it is reversed. It can be homozygous or heterozygous. Homozygous inversions are balanced, they can pair with sister chromatids at the time of crossing over. However, heterozygous inversions cause errors in crossing over, leading to production of unbalanced and unviable gametes. This affects the fertility of the individual.

C.Ans : Inversion generally do not cause genetic defects are there is no loss or gain of genes, only rearrangement of their position on the chromosome. However, if inversion occurs by breaking away of chromosome at a region within a gene, that gene sequence is changed and it becomes defective. In such cases, homozygous inversion can cause a defect.