The lack of independent assortment of two genes A and B in fruit fly Drosophila is due to linkage. Linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together.

Explanation:

Linkage is the phenomenon where genes located near each other on the same chromosome tend to be inherited together more frequently than expected by chance. This is because during meiosis, when the chromosomes separate and are distributed into gametes, the genes on the same chromosome are less likely to undergo recombination or independent assortment.

1. Independent Assortment:
Independent assortment is the principle that states that alleles of different genes segregate independently of one another during the formation of gametes. This means that during meiosis, the genes for different traits are randomly sorted into gametes, resulting in various combinations of alleles.

2. Linkage:
Linkage occurs when genes are located on the same chromosome and are physically close to each other. When genes are closely linked, they tend to be inherited together and do not assort independently.

3. Crossing Over:
Crossing over is the exchange of genetic material between homologous chromosomes during meiosis. It occurs during prophase I of meiosis and results in the exchange of genetic material between the non-sister chromatids of homologous chromosomes. Crossing over can break the physical connection between genes on the same chromosome, leading to recombination and independent assortment.

However, if the genes are closely linked and do not undergo crossing over, they will be inherited together more frequently. In the case of the fruit fly Drosophila, the lack of independent assortment of genes A and B suggests that they are closely linked on the same chromosome and do not undergo crossing over frequently.

In conclusion, the lack of independent assortment of genes A and B in Drosophila is due to linkage, which means that they are located close to each other on the same chromosome and tend to be inherited together. This phenomenon can be explained by the fact that these genes do not undergo recombination or crossing over frequently.

The lack of independent assortment in sweet pea and Drosophila is due to linkage.