the green-nose fly normally has six chromosomes: two metacentric and four acrocentric. A geneticist examines the chromosomes of an odd-looking green-nose fly and discovers that it has only five chromosomes; three of them are metacentric and two are acrocentric. Explain how this change in chromosome number might have taken place.

Robertsonian fusion

Explanation:

The Robertsonian (Rb) fusion is a type of chromosome rearrangement that involves the centric fusion of two acrocentric chromosomes to give rise to a metacentric. The normal chromosome number was six with two metacentri which increased to three in the odd looking fly and also the acrocentric which reduced from four to two.

Thus, it can be suggested that two of the four acrocentric chromosomes have fused either by telomere inactivation or loss in the process of Rb fusion reducing the number of acrocenric chromosomes and then produced a metacentric increasing the number of metacentrics.