Question

16. The maternal copy of chromosome 19 has undergone an inversion such that its new ordering is as follows:

A-*-B-E-D-C-F(* denotes the centromere).

The normal ordering of the paternal copy is as follows:

a-*-b-c-d-e-f.

According to the location of the affect chromosome region with respect to the centromere, how would this inversion be classified?

17. Assume the crossing over occurs between d and e during meiosis. Denote all possible monads in the gametes using the asterisk and upper and lower-case letters as above.

18. Gametes containing which of the above monads would NOT be expected to be viable?

Answer 1

1. A paracentric ("away from the center") inversion does not include the centromere. In above example C and E have inversed and since these are not located near the centromere, this is a example of paracentric inversion.
2. Suppose there are 2 chromosomes, A-*-B-C-D-E-F and a-*-b-c-d-e-f. Possible combinations of chromosomes formed during meiosis if 'd' and 'e' crossover are as follows:

• A-*-B-C-D-E-F, a-*-b-c-d-e-f (normal chromosomes which do not crossover)
• A-*-B-C-d-e-F ('d' and 'e' from the other chromosome crossover and recombine), a-*-b-c-D-E-f ('D' and 'E' from the other chromosome crossover and recombine).

3. Non-viability is only when a important gene which is essential for survival (ex. House-keeping genes) is missing. Since in the above crossover deletion of any gene is not occuring and hence, all the monads will be viable.