A testcross of F
1
flies produces a 1:1 ratio of
brown,thin
and
red,heavy
F
2
, with no
recombinants
.
If the genes were
not linked
, the testcross would have produced
four
phenotypes.
A testcross of F1 flies produces a 1:1 ratio of
brown,thin and red,heavy F2, with no recombinants.