When doing a genetic cross why is it necessary to remove the parent flies before the pupae have hatched?

Answer 1

Usually, the parent flies will have a different genotype to the F1 generation (their offspring).

For example, if the parents had WW (black eyes) and ww (white eyes), their offspring would all have Ww (black eyes). If you were experimenting further, you would want the F1 generation to cross - with Ww X Ww. If you did not remove the parental generation, you could have crosses between them and the F1 generation, which would result in different genotypes.

If the parents were not removed, you could have the following crosses:

Ww X WW

Ww X ww

WW X ww

Ww X Ww

The only cross that you would desire in the experiment would be F1 X F1 (Ww X Ww), which would give you the desired genotypes for the F2 generation.

Answer 2

It is necessary to remove parent flies before the pupae hatch to prevent them from interfering with the offspring. The parent flies might eat the pupae or contaminate the breeding environment, leading to inaccurate results in the genetic cross.