A rice breeder is working with two traits: dwarfness, and resistance to a fungal
ID: 314604 • Letter: A
Question
A rice breeder is working with two traits: dwarfness, and resistance to a fungal disease. (Rice is self-pollinated). DD results in dwarf plants, Dd plants arc semidwarf and dd plants are tall. The disease resistance is controlled by a single gene and RR and Rr plants are resistant and pi = susceptible. The breeder crosses the following parents: P_1 = DDRR, and P_2 = ddrr. The breeder's objective is to select a dwarf, disease resistant line. Show the genotypic and phenotypic ratios the breeder expects in the F_2 from this mating. Explain why the F_2 phenotypic ratio in part (a) is not a 9:3:3:1 ratio. Show how the breeder will identify the desired line. What is this procedure called?Explanation / Answer
Answer:
DDRR (dwarf, resistant) x ddrr (tall, suscepatiable)------Parents
DR dr ---------------------------------Gametes
DdRr (semidwarf, resistant) ---F1
F1 x F1
DR
Dr
dR
dr
DR
DDRR(dwarf, resistant)
DDRr(dwarf, resistant)
DdRR(semidwarf, resistant)
DdRr(semidwarf, resistant)
Dr
DDRr(dwarf, resistant)
DDrr(dwarf, susceptable)
DdRr(semidwarf, resistant)
Ddrr(semidwarf, susceptable)
dR
DdRR(semidwarf, resistant)
DdRr(semidwarf, resistant)
ddRR (tall, resistant)
ddRr (tall, resistant)
dr
DdRr(semidwarf, resistant)
Ddrr(semidwarf, susceptable)
ddRr (tall, resistant)
ddrr(tall, susceptable)
6a). Phenotypic ratio: 3 : 6 : 3 : 1: 2 : 1
dwarf, resistant: semidwarf, resistant : tall, resistant : dwarf, susceptible : semidwarf, susceptible : tall, susceptible
Genotypic ratio: DDRR : DDRr : DdRR : DdRr : ddRR : ddRr : DDrr : Ddrr : ddrr
1 : 2 : 2 : 4 : 1 : 2 : 1 : 2 : 1
b) Due incomplete dominance in the height of the rices, there was deviation of F2 phenotypic ration from 9:3:3:1
DR
Dr
dR
dr
DR
DDRR(dwarf, resistant)
DDRr(dwarf, resistant)
DdRR(semidwarf, resistant)
DdRr(semidwarf, resistant)
Dr
DDRr(dwarf, resistant)
DDrr(dwarf, susceptable)
DdRr(semidwarf, resistant)
Ddrr(semidwarf, susceptable)
dR
DdRR(semidwarf, resistant)
DdRr(semidwarf, resistant)
ddRR (tall, resistant)
ddRr (tall, resistant)
dr
DdRr(semidwarf, resistant)
Ddrr(semidwarf, susceptable)
ddRr (tall, resistant)
ddrr(tall, susceptable)
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.