A researcher is curious if Bt resistant bollworms are susceptible to an insecticide called DDT. Bollworms susceptible to Bt have genotype RR or Rr, whereas those resistant to Bt have genotype rr. Bollworms susceptible to DDT have genotype tt, whereas bollworms resistant to DDT have genotypes Tt or TT. In an effort to better understand how these two genes are inherited, the researcher crosses an RR tt bollworm with an rr TT bollworm to produce the F1 generation. Then, the researcher crosses the F1 generation to produce an F2 generation. What proportion of the F2 generation is resistant to both Bt and DDT

It is given that bollworms that are susceptible to Bt are represented by either RR or Rr and resistance one are shown by rr genotype and bollworms that are resistant to DDT are represent TT or Tt genotype and susceptible to DDT have tt genotype.

Cross: RR tt with rr TT

Gametes: Rt and rT

F1 cross:

RT

rT RrTt ( susceptible Bt and resistant DDT)

F1 Cross with F1

Gametes: RT, Rt, rT and rt

cross:

RT Rt rT rt

RT RRTT RRTt RrTT RrTt

Rt RRTt RRtt RrTt RrTt

rT RrTT RrTt rrTt rrTt

rt RrTt Rrtt rrTt rrtt

The bold genotypes are the three out of 16 that are resistant to both DDT and Bt.