Question

Can someone please help me answer this question, and teach me how to do it step by step? I am currently taking genetics and am extremely confused.

In Drosophila, the genes y, f, and v are all X-linked. Females who are homozygous for recessive alleles of all three genes (y f v / y f v) are crossed to wild-type males (y⁺ f⁺ v⁺ /y⁺ f⁺ v⁺ ). The resulting trihybrid F1 females are test-crossed.

The F2 are distributed as follows:

y f v	3210
y f v+	72
y f+ v	1024
y f+ v+	678
y+ f v	690
y+ f v+	1044
y+ f+ v	60
y+ f+ v+	3222
Total	10,000

Which of the following linkage maps correctly shows the order of the y, f, and v genes?

a) y————v————f  

b) f————y————v

c) y————f————v

d) y————v————f and f————y————v are equally accurate

e) All three maps are equally likely