A researcher is curious if Bt resistant bollworms are susceptible to an insectic

Question

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 bollworms 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? Fill in the Punnet squares by dragging and dropping alleles to the answer boxes, first to predict the offspring in the F1 generation and then to predict the offspring in the F2. Generation. Then full in the blanks using the product rule. (Assume that the genes that determine DDT resistance and BT resistance are on different chromosomes.)

Explanation / Answer

Bullworm susceptible to Bt (SB) - RR, Rr

Bullworm Resistant to Bt (RB) - rr

Bullworm susceptible to DDT(SD) - tt

Bullworm resistant to DDT (RD )- Tt, TT

Cross between RRtt (SB - SD) x rrTT (RB - RD)

F1 : RrTt (all SB-RD)

F2 : RrTt x RrTt

RRTT

SB-RD

RRTt

SB-RD

RrTT

SB-RD

RrTt

SB-RD

RRTt

SB-RD

RRtt

SB-SD

RrTt

SB-RD

Rrtt

SB - SD

RrTT

SB-RD

RrTt

SB-RD

rrTT

RB-RD

rrTt

RB-RD

RrTt

SB-RD

Rrtt

SB-SD

rrTt

RB-RD

rrtt

RB-SD

Ratio for F2 generation - SB-RD : SB-SD : RB-RD : RB-SD

9:3:3:1

RT Rt rT rt RT

RRTT

SB-RD

RRTt

SB-RD

RrTT

SB-RD

RrTt

SB-RD

Rt

RRTt

SB-RD

RRtt

SB-SD

RrTt

SB-RD

Rrtt

SB - SD

rT

RrTT

SB-RD

RrTt

SB-RD

rrTT

RB-RD

rrTt

RB-RD

rt

RrTt

SB-RD

Rrtt

SB-SD

rrTt

RB-RD

rrtt

RB-SD

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