The other mutation we'll be mapping, B101, is a transposon insertion mutation. One question to ask about any newly-discovered mutation is whether it is homozygous viable. What does "homozygous viable" mean? If a mutation is a recessive lethal, then any fly carrying two copies of that mutation (one on each homologous chromosome) will die. Maybe as an embryo, maybe as a larva, pupa, or even an adult, but it won't survive to reproduce. If this is not the case — if animals homozygous for a mutation can survive and reproduce — we say that this mutation is "homozygous viable."
1. B101 is on the 2nd chromosome. I crossed it to flies with the genotype CyO/Sp; TM6B/Sb (I'm ignoring the X chromosomes since they're irrelevant for this problem). I then selected progeny which had curly wings, were tubby, had extra humeral bristles, and carried the B101 mutation. Write out the genotype of these progeny flies.
2. How many different gametes can these flies produce (again, we only care about the 2nd and 3rd chromosomes here).
3. Now draw out the Punnett square for an inter se cross among these flies.
4. Given that the Curly, Humeral, and Tubby mutations are all homozygous lethal, what are the expected phenotypes and ratios of the progeny of this cross if the B101 mutation is homozygous lethal, too?
5. What are they if your mutation is homozygous viable?