Question

In Drosophila, crossing over occurs in females but not in a male. Gene A and B are 10 map units apart on the chromosome. A female Drosophila is with genotype ${AB}/{ab}$ and male Drosophila with genotype ${AB}/{ab}$. 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

Crossing over, in other terms, is the exchange of fragment seen in homologous chromosomes between non-sister chromatids and occurs while the pachytene stage of the prophase I within the cell division process of meiosis and always occurs within a linkage group.

Complete answer:
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 almost one another have less probability of being separated into 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 2n where "n" is the number of genes for which the person is heterozygous. Female Drosophila is heterozygous for two gene pairs and exhibits cross over, thus it'll form a complete of 4 sorts of. These are AB, ab, Ab, and aB. Since male Drosophila doesn't show crossover, it'll form a complete of two parental sorts of gametes; AB and ab.

Additional Information: In most eukaryotes, a cell carries two versions of every gene, each mentioned as an allele. Each parent passes on one allele to every offspring. An individual gamete inherits a complete haploid complement of alleles on chromosomes that are independently selected from each pair of chromatids lined up on the metaphase plate. Without recombination, all alleles for those genes linked together on an equivalent chromosome would be inherited together. Meiotic recombination allows more independent segregation between the 2 alleles that occupy the positions of single genes, as recombination shuffles the allele content between homologous chromosomes.
So, the correct answer is ‘4 types: 2 types’.

Note: Crossing over was described, in theory, by Thomas Hunt Morgan. He relied on the discovery of Frans Alfons Janssens who described the phenomenon in 1909 and had called it "chiasmatypie".The recombination of linked genes that cross overproduces plays a significant role in evolution. Crossing over and DNA repair are very similar processes, which utilize many of equivalent protein complexes.