Question

A Xw+m+Xwm female was mated to a XwmY male. Out of 1000 total F1 progeny there were 230 flies that were otherwise wild type with white eyes and 240 flies that were otherwise wild type with miniature wings. What is the distance between the genes for eye color and wing length?

Answer 1

In order to calculate the distance between two alleles/genes that are found in the same chromosome, we need to know how often crossing-over happened (recombination frequency). We know from the text that white eyes were linked to miniature wings and that wild type eyes were linked to wild type wings, so any phenotype that's contrary to these parent combinations are a result of crossing-over. We know then that 230 flies + 240 flies were a result of such recombination. To calculate the recombination frequency we only need to divide these flies (total of recombinant flies) by the total of flies in the offspring and turn it into percentage.
$\frac{230+240}{1000}$=0.47
0.47*100%=47%
47 map units is the distance between the genes for eye color and wing length.