plant pathology-genetics

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Question details:

1(a).  Fill in the expected frequencies of F2progeny resulting from a cross of R1R2/R1R2 × r1r2/r1r2 given a recombination frequency (r) of 0.1.  (10 points)

 

 

R1R2

R1r2

r1R2

r1r2

R1R2

 

 

 

 

R1r2

 

 

 

 

r1R2

 

 

 

 

r1r2

 

 

 

 

 

 

2.  You make a test cross from the following cross: R1R2/R1R2 × r1r2/r1r2

(That is, you cross the F1from the above cross to an r1r2/r1r2 plant). Both R1 and R2 are dominant resistance genes.  You inoculate the progeny with a pathogen race that is avirulent on both R1 and R2 (it carries avirulence genes Avr1 and Avr2).  You get 95 susceptible progeny out of 200 test cross progeny.  What is the recombination distance between R1 and R2? (2 points)

 

 

3.  You make an F2 cross with the F1 progeny from parental genotypes R1r2/R1r2 × r1R2/r1R2 and inoculate the progeny with a pathogen race that is avirulent on both R1 and R2 (it carries avirulence genes Avr1 and Avr2).  You get 3 susceptible progeny out of 200 test cross progeny. What is the recombination distance? (2 points)

 

4.  What are the expected R:S segregation ratios for progeny from (1) an F2 crossand (2) a test crossgiven each of the following senarios (10 points):

(a)  A pathogen genotype of Avr1, Avr2 and duplicate dominant epistasis between two independent R genes (R1 and R2) from separate parents.

(b)  A pathogen genotype of Avr1, Avr2 and duplicate dominant epistasis between two tightly linked R genes (R1 and R2) in coupling (cis) phase.

(c)  A pathogen genotype of Avr1, Avr2 and duplicate dominant epistasis between two tightly linked R genes (R1 and R2) in repulsion (trans) phase.

(d)  An avirulent pathogen genotype and complementary epistasis between two independent R genes.

(e)  A necrotrophic pathogen genotype of Tox1, Tox2 and two independent susceptibility genes (S1 and S2), when either gene produces susceptibility.

 

 

F2

Test Cross

(a)

 

 

(b)

 

 

(c)

 

 

(d)

 

 

(e)

 

 

 

 

 

 

5.  You self an F1 plant that is heterozygous for two dominant resistance genes, R1 and R2 and inoculate the F2 progeny with a pathogen race that is avirulent on both R1 and R2 (it carries both avirulence genes Avr1 and Avr2).  You get 40 susceptible progeny out of 200 total progeny.

(a)  What is the linkage phase for these two genes? (1 point)

(b)  What is the recombination distance? (1 point)

 

 

6.  You self an F1 plant that is heterozygous for two dominant resistance genes (R1 and R2) and inoculate the F2 progeny with a pathogen race that is avirulent on both R1 and R2 (i.e., it carries avirulence genes Avr1 and Avr2).  You get 6 susceptible progeny out of 200 total progeny.

(a)  What is the linkage phase for these two genes? (1 point)

(b)  What is the recombination distance? (1 point)

 

 

7.  You make a test cross between an F1 plant that is heterozygous for two dominant resistance genes (R1 and R2) and a line that is homozygous recessive at both loci, and inoculate the progeny with a pathogen race that is avirulent on both R1 and R2 (i.e., it carries avirulence genes Avr1 and Avr2).  You get 50 susceptible progeny out of 200 test cross progeny.

(a)  What is the linkage phase for these two genes? (1 point)

(b)  What is the recombination distance? (1 point)


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