In cross I we are treating F1 x dp se cross b and dp se x F1

In cross I, we are treating F1 x dp se (cross [b]) and dp se   x   F1 (cross [c] ) as equivalent crosses, but in Drosophila that is generally a very bad idea! Why is it a bad idea in general and why will we be able to get away with it in cross I? (3 points)

Cross B is (F1 virgin females X dp;se males)

Cross C (dp;se virgin females X F1 males)

Solution

The dp-dumpy or truncated wings are chromosome II mutant type. The se-sepia eye or black eyed are chromosome III mutant type. The cross is dihybrid cross with two non linked pair of traits. In this type of cross the mutant alleles are on two different chromosomes II and III. The first dihybrid cross is between male with homogeneous with sepia (se) eyes and dumpy (dp) wings with females with both wild traits. This P1 generation with all are heterogenous traits.

In the F1 generation all the gametes are ++, dp+, se+ and dpse. In Drosophila the crossing the F1 gametes with dese is a bad idea because the results produced are all mutants. So this cross is bad in general.

In Cross B (F1 virgin females X dp;se males) i.e, F1 virgin female with dp;se male (multichromosomal mutant) as the F1 virgin females the cross produces heterogeneous traits. The resultant flies are phenotypically 50% normal. As the traits are recessive.

In Cross C (dp;se virgin females X F1 males) i.e, in this case multichromosomal mutant virgin female with F1 males the cross produces homogeneous and hetergeneous traits. All the flies are phenotypically normal.