Linkage in Drosophila

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                                                           Linkage in Drosophila


In Drosophila, grey colour(G) is dominant over black colour (g) and long wing (L) is dominant over vestigial wing (l). The genes for these two characters (colour of the body and length of the wings) are linked together in the same chromosome.

The linked genotypes of the parents are written as follows:

Grey long-GL/GL

Black vestigial-gl/gl

When a fly with grey body and long wings (GGLL) is crossed with another fly having black body and vestigial wings (ggll), all the F, individuals are having grey body and long wings (GgLI). When F, male hybrid is test crossed with the double recessive parent, the F, contains only two types of individuals in equal numbers (1:1 ratio) instead of the expected 1:1:1:1 dihybrid test cross ratio. In the F2 generation, all the flies are like their parents. There are no new combinations. This is because the gene G is linked with L in one chromosome and the genes g and I are linked in another chromosome. Hence during gamete formation, they cannot segregate independently. Hence only two types of gametes are formed resulting the formation of two types of combinations in F2. The resulting offspring are resembling the grand parents. This because gene G is linked with L and the gene g is linked with l.


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