You Are Mapping the Location of Two Genes in Drosophila,listless

Multiple Choice

You are mapping the location of two genes in Drosophila,listless l and blind b.(l⁺ l⁺ b⁺ b⁺) and (l⁺ l b⁺ b) flies are normal,but (l l b b) flies don't move around very much and cannot detect the location of a light source.You perform a cross between a true-breeding normally active,sighted fly and a true-breeding listless,blind fly.You testcross an F1 individual with an individual homozygous recessive for both traits and get the following results:
Listless,sighted: 100
Listless,blind: 400
Normal activity,sighted: 400
Normal activity,blind: 100
The recombination frequency observed in experimental crosses can be used to indicate distances between genes on a chromosome.More specifically,the map distance in map units between two genes is equal to the frequency of recombinant offspring.What is the distance between these two genes?

A) They are on different chromosomes.
B) They are 10 map units apart.
C) They are 20 map units apart.
D) They are 40 map units apart.
E) They are 80 map units apart.