Question

An individual has the chromosomes below where the dot represents the centromere:

ABCDEFG.H AEDCBFG.H

If a crossover event occurs between the B and C loci, what is the longest chromosome formed?

Enter your answer with no spaces between the loci and use a period as the centromere.

Answer 1

This is an example of paracentric inversion, where the crossing over takes place within an inversion loop, which does not contain the centromere. The resulting gametes may either contain

1) the normal chromatid ABCDEFG.H

2) the inverted chromatid AEDCBFG.H

3) the acentric fragment ABCDEA

4) the dicentric chromatid H.GFEDCBFG.H (the longest chromosome)

The picture below summarises the cross over event for the given chromosome.