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During a cross between two individuals, the alleles of a particular gene get segregated according to Mendel’s law. The law of segregation suggests that each gene gets dispersed in the offsprings, independent of each other. Most of the genetic research has been done on the Drosophila melanogaster since the function of the mutated genes can be studied easily in this organism.
Explanation of Solution
The cross between gray body, short legs (DDbb) and dark body long legs (ddBB) is represented as follows in Figure 1.
Figure 1: A cross between gray body, short legs (DDbb) and dark body long legs (ddBB), representation of F1 and F2 generations, assuming that there is no crossing-over during self-fertilization.
From Figure 1, it is clear that all the offsprings produced in F1 generation have a gray body and long legs and they have DdBb genotype. A self-cross among the F1 generation offsprings to produce F2 generation is represented as follows:
When there is no crossover, the recombinants like ddbb will not be produced and only the parental genotypes are produced. Hence, in the absence of no-cross over, the ratio of genotype in F2 generation is 1:2:1, that is, 25% DDbb, 50% DdBb, and 25% ddBB. The phenotypes of the F2 generation are 25% long legs, black body; 50% long legs, gray body, and 25% short legs, gray body.
Thus, it can be concluded that in the F1 generation, 100% of the offsprings are the gray body and short legs. In F2 generation, in the absence of crossover, the genotypic ratio between organisms is 1:2:1 and the phenotypes produced are long legs, black body; long legs, gray body; and short legs, gray body.
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Life: The Science of Biology
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