In corn, the following three alleles are recessive to their normal phenotypes. a

Question

In corn, the following three alleles are recessive to their normal phenotypes.

anther (an); brachytic (br); fine (f)   An F1 (with a normal phenotype) that was heterozygous for all three of these loci was testcrossed.

The following progeny phenotypes were obtained:

366 anther

372 brachytic, fine

83   completely normal

64   anther, brachytic, fine

19   fine

17   anther, brachytic

2     brachytic

2anther, fine

a.what were the genotypes of the parents of the F1?

b.Draw a linkage map for the three genes (assume they are linked)

(determine order and map units)

Explanation / Answer

Based on the given data, the genotypic notations are

The genotype of an F1 individual heterozygous for all three of these loci is: an an+ br br+ f f+ was testcrossed with complete recessive parent with the genotype an an br br f f.

The obtained progeny is:

S.no

Phenotype

Number of progeny

Type of recombinant

1

anther

366

Parental

2

brachytic, fine

372

Parental

3

completely normal

83  

Single recombinant

4

anther, brachytic, fine

64  

Single recombinant

5

fine

19  

Single recombinant

6

anther, brachytic

17  

Single recombinant

7

brachytic

2

Double recombinant

8

anther, fine

2

Double recombinant

                                           Total = 742

The formula for calculation of map distance is:

So, the F1 parental genotypes are as follows:

+ + + : (wild-type)

an br f:

From these sums it is clear that the “br/+” locus lies between the “an/+” locus and the “r/+” locus.

There are 83 + 2 + 64 + 2 = 151 progeny show recombination between genes an and br.

Thus, the gene distance between an and br is 20.3 map units (m.u).

There are 19 + 2 + 17 + 2 = 40 progeny show recombination between genes br and f.

Thus, the gene distance between br and f is 5.3 (m.u), and the gene distance between an and f is (20.3+5.3= 25.6 m.u).

The genetic map of the three genes is as follows:

S.no

Phenotype

Number of progeny

Type of recombinant

1

anther

366

Parental

2

brachytic, fine

372

Parental

3

completely normal

83  

Single recombinant

4

anther, brachytic, fine

64  

Single recombinant

5

fine

19  

Single recombinant

6

anther, brachytic

17  

Single recombinant

7

brachytic

2

Double recombinant

8

anther, fine

2

Double recombinant

                                           Total = 742

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