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A genetic map of D. melanogaster is illustrated in 4 FIGURE 7.15.

Interference and coefficient of coincidence Map distances give us information not only about the physical distances that separate genes, but also about the proportions of recombinant and nonrecombinant gametes that will be produced in a cross. For example, knowing that genes st and ss on the third chromosome of D. melanogaster are separated by a distance of 14.6 m.u. tells us that 14.6% of the gametes produced by a fly heterozygous at these two loci will be recombinants. Similarly, 12.2% of the gametes from a fly heterozygous for ss and e will be recombinants.

Theoretically, we should be able to calculate the proportion of double-recombinant gametes by using the multiplication rule of probability (Chapter 3), which states that the probability of two independent events occurring e e e e e e e e e

Chromosome 1 (X)

Chromosome 3

Net veins

Chromosome 3

Net veins

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