Chapter 5, Problem 30P

A $\text{Drosophila}$ experiment examining potential geneticlinkage of $\text{X-linked}$ genes studies a recessive eye mutant(echinus), a recessive wing-vein mutation (crossveinless),and a recessive bristle mutation (scute). The $\text{wild-type}$ phenotypes are dominant. Trihybrid $\text{wild-type}$ females (allhave the same genotype) are crossed to hemizygous malesdisplaying the three recessive phenotypes. Among the $\text{20,765}$ progeny produced from these crosses are the phenotypes and numbers listed in the table. Any phenotypenot given is wild type.

$\begin{array}{cc}\text{Phenotype}& \text{Number}\\ \text{1}\text{. Echinus}& \text{8576}\\ \text{2}\text{. Scute}& \text{977}\\ \text{3}\text{. Crossveinless}& \text{716}\\ \text{4}\text{. Echinus, scute}& \text{681}\\ \text{5}\text{. Scute, crossveinless}& \text{8808}\\ \text{6}\text{. Scute, crossveinless, echinus}& \text{4}\\ \text{7}\text{. Echinus, crossveinless}& \text{1002}\\ \text{7}\text{. Echinus, crossveinless}& \text{1}\\ & \text{20765}\end{array}$

a. Determine the gene order and identify the alleles on thehomologous X chromosomes in the trihybrid females.

b. Calculate the recombination frequencies between eachof the gene pairs.

c. Compare the recombination frequencies and speculateabout the source of any apparent discrepancies in therecombination data.

d. Use $\text{chi-square}$ analysis to demonstrate that the datain this experiment are not the result of independentassortment.