A rice breeder is working with two traits dwarfness and resi

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?

Solution

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)