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
The correct answer is - 3/16 or 18.75% portion will be resistant to both Bt and DDT.
Explanation:
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.
Cystic Fibrosis is a recessive disease. It could most likely skip several generations. If the two people have the disease then were to have children, each child has a 25% chance of being born with the disease.
