Question

In Drosophila, crossing over occurs in female but not in a male. Gene A and B are 10 map unit apart on the chromosome. A female Drosophila is with genotype $\frac{AB}{ab}$ and male Drosophila with genotype $\frac{AB}{ab}$. Then how many types of gametes are produced by female and male Drosophila respectively?

• A. 4 types: 2 types
• B. 2 types : 2 types
• C. 4 types : 4 types
• D. 4 types: one types

Answer 1

The correct option is A 4 types: 2 types

The linkage is referred to as the phenomenon wherein alleles located close together on a chromosome show a tendency to be inherited together during meiosis. Genes present near to each other have less probability of being separated onto different chromatids during the chromosomal crossover. Therefore, when a cluster of genes shows linkage behavior they do not show independent assortment.

The total possible type of gametes produced by an organism is 2${}^n$ where "n" is the number of genes for which the person is heterozygous. Female Drosophila is heterozygous for 2 gene pairs and shows cross over, thus it will form a total of four types of gametes ( 2${}^2$=4; two parental types and two recombinants). These are AB, ab, Ab, and aB. Since male Drosophila does not show cross over, it will form a total of two parental types of gametes; AB and ab.

So, the correct answer is option A.