In a diploid plant species, and F1 with the genotype Gg Ll Tt is test-crossed to a pure-breeding recessive plant with the genotype gg ll tt. The offspring genotypes are listed in the table below:

Genotype Number

Gg Ll Tt 653

Gg Ll tt 5

Gg ll Tt 78

Gg ll tt 116

gg Ll tt 121

gg Ll tt 75

gg ll Tt 4

gg ll tt 548

Total= 1600

1) What is the order of these three linked genes?

A) L-G-T

B) G-T-L

C) G-L-T

2) Calculate the recombination fraction between G and T pair of a gene. Enter answer to three decimal places (example 0.235)

3) Calculate the recombination fraction between T and L pair of a gene.

4) Calculate the recombination fraction between G and L pair of a gene

5) What is the interference value for this data set?

1) G-T-L; 2) RF = 15.375mu; 3) RF = 10.125 mu; 4)RF = 25.5 mu; 5) Interference = 63.873%

Explanation: 1) To define the order of genes, we have to identify no-crossovers, single crossovers and double crossovers among the genotype numbers. Because there is a higher probability of not having crossover, the genotype with higher number will be no crossover. On the other hand, the offsprings with the lowest numbers will be double crossover. So,

In order for this last two to be a double crossover, comparing to the no crossover, the allele T must be in the center. Thus, the order is G-T-L.

The others are single crossovers.

2) Recombination frequency (or fraction) is a percentage of recombination an allele can have. It can also determine the distance between genes.

The recombination fraction between G and T is: RF = () . 100

where P is the double crossover between G and T and R is the single crossover between the same genes;

Single crossover G-T = 121+116

RF₁ = . 100 = 15.375 mu (map unit)

3) RF for T-L:

In this case, P is the double crossover between T and L and R is the single crossover between them:

Single crossover T-L = 78 + 75 = 153

RF₂ = .100 = 10.125 mu

Note: T represents the total of individuals from the experiment, in this case T = 1600.

4) As the order of the genes is G-T-L and RF also represents the distance between genes, the recombination fraction between G and L is

RF₃ = 15.375 + 10.125 = 25.5 mu.

5) Interference value = 1 - coefficient of coincidence

Coefficient of coincidence = . 100

expected double crossover = = 1.557

coefficient of coincidence = . 100 = 36.127%

Interference value = 1 - 0.36127 = 0.63873

Interference value = 63.873%

is this for the e2020 class

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