Mapping traits to a chromosome
Fruit flies have four chromosomes. Fruit flies also have anumber of body markers that are useful for mapping genes to givenchromosomes. Chromosome I is the X chromosome, which has eye coloralleles w+ (red eyes, dominant) and w- (white eyes, recessive).Curly O (Cyo), located on chromosome II, is a dominant markermutation which causes the wings to curl on the ends instead ofbeings straight (WT). Stubble (Sb), a dominant marker mutationlocated on chromosome III, causes the fly’s normally (WT) long andslender bristles to be short and stubbly. (Chromosome IV is verytiny, and has very few genes on it, so we'll ignore it for thisproblem.)
You have a new mutation that causes the fly to have fourantennae instead of two, which you've named double. This mutationis dominant to the wild type allele (two antennae). You want toknow which chromosome it is on, so you perform tests for linkage ofdouble to the three markers on the three major chromosomes. Assumeall parents are pure-breeding.
Cross I: Test for linkage with white You cross a white-eyedfemale with two antennae to a red-eyed male with four antennae.Offspring: 405 females with red eyes and four antennae 399 maleswith white eyes and four antennae
Cross 2: Testing for linkage with CyO and Sb You cross a flywith four antennae to a fly with curly wings and stubbly bristles.The offspring all have four antennae, curly wings, and stubblybristles. You cross one of these F1 hybrid offspring to a WT fly(all recessive), and get the following outcomes: 226 curly wings,stubbly bristles, two antennae 224 straight wings, stubblybristles, two antennae 223 curly wings, long bristles, fourantennae 227 straight wings, long bristles, four antennae 23 curlywings, stubbly bristles, four antennae 24 straight wings, stubblybristles, four antennae 26 curly wings, long bristles, two antennae27 straight wings, long bristles, two antennae
To which of the three markers is double linked?
Which chromosome is it on?
Calculate the distance between double and that marker, showingyour calculations below.

