Question

Two homologous chromosomes are depicted in the diagram given below. Crossing over occurs between chromatid 2 and chromatid 3 at the point as depicted.

The gametes produced as a result of this crossing over will be

• A. Ab and aB
• B. AB and ab
• C. Ab, AB, ab and aB
• D. Ab, aB and ab

Answer 1

Answer: (C)

Crossing over occurs between non-sister chromatids of homologous chromosomes during the pachytene phase of meiosis I. In this example, after crossing over, chromosome number 1 will have one chromatid with Ab and another chromatid with AB. Chromosome number 2 will have one chromatid with ab and another chromatid with aB. In anaphase 1, one of these chromosomes will go in one cell and the other will go in another cell. Then in anaphase 2, the centromere of these chromosomes will split leading to the formation of four cells one with Ab, the other with AB, the third with ab and the fourth with aB.