Explain how mitotic recombination leads to the mosaic condition termed twin spots.

If an individual Drosophila has two or more populations of cells comprising different genotypes from one single egg then it is termed as twin spots or mosaic.

Explanation:

There might be different reasons for mosaic to occur like

Nondisjunctioning of the chromosomes

Lag in anaphase

Endoreplication

Mutations in a single cell

Mitotic recombination:

One of the major ways through which mosaic or twin spots arise is the mitotic recombination. It is also termed as somatic cross over. Twin spot or mosaic generally occurs if there is linking of heterozygous genes in repulsion. The recombination generally happens among the centromeres from the adjacent genes.

A common example of the mitotic recombination is the Bloom's syndrome. Bloom's syndrome is caused due to the mutation that occurs in the blm gene. As a result, there are defects in the BLM protein produced.