Gene mapping & recombination frequencies

A Drosophila experiment examining potential genetic linkage of X-linked genes studies a recessive eye mutant (echinus), a recessive wing-vein mutation (crossveinless), and a recessive bristle mutation (scute). The wild-type phenotypes are dominant. Trihybrid wild-type females (all have the same genotype) are crossed to hemizygous males displaying the three recessive phenotypes. Among the 20,785 progeny produced from these crosses are the phenotypes and numbers listed in the table. Any phenotype not given is wild type.



a) Determine the gene order on the homologous X chromosomes in the trihybrid females
b)Calculate the recombination frequencies between each of the gene pairs.
c)Compare the recombination frequencies and speculate about the source of any discrepancies in the recombination data.
d)Use chi-square analysis to demonstrate that the data in this experiment are not the result of independent assortment.