The recessive alleles k (kidney-shaped eyes), c (cardinal-colored eyes), and e (

Question

The recessive alleles k (kidney-shaped eyes), c (cardinal-colored eyes), and e (ebony body color) identify three genes on the same chromosome in Drosophila. Females with kidney-shaped, cardinal-colored eyes were mated with ebony males. The F1 were all wild-type. When F1 females were testcrossed with ebony males with kidney-shaped, cardinal-colored eyes, the following progeny phenotypes were obtained 784 790 149 144 68 70 3 a. Determine the order of genes and the map distances between them. (3 pt) b. How much interference in double-recombination is there? (1

Explanation / Answer

k c E 784

K C e 790   

K c e 149

k C E 144

K c E 68

k C e 70

K C E 3

k c e 6   

Total population = 2014

In any double cross, the maximum number of progeny is the progenies which have the same genotype as that of the parents and the progeny which have the least number is the progeny which are the result of a double crossover. So looking at the progenies we can easily conclude that k c E and K C e  are the original parent type and K C E and k c e are the double recombinant.

This also gives us the idea about the gene which is present in the middle as only the middle gene is transferred to the other chromosome during the double crossover. So the middle gene is E

The distance between C and E

If we want to find the distance between the C and E then we need to find out the crossover frequency and divide it by the total number of progeny

K c e 149

k C E 144

K C E 3

k c e 6

Linkage distance = total number of recombinant * 100 / total number of progeny

302 * 100/ 2014

= 15

So, map distance between C and E is 15 map units or 15cM

The distance between E and K.

If we want to find the distance between the E and K then we need to find out the crossover frequency and divide it by the total number of progeny

K c E 68

k C e 70

K C E 3

k c e 6  

Linkage distance = total number of recombinant * 100 / total number of progeny

147*100/ 2014

=7.29

So, map distance between E and K is 7.29 map units or 7.29cM

Allelic arrangement is the first parent is K E C

Since the flies have undergone the double recombination so we can expect the recombination interference

In order to find out the recombination interference we need to find out the coefficient of coincidence (c.o.c.)

Coefficient of coincidence is given by

the observed frequency of double recombinant/ expected frequency of double recombinant

expected frequency of double recombinant is given by

Map distance between E and K /100 * map distance between E and C /100 = 15/100*7.29/100 = 0.0109

Observed frequency of double recombinant = 3+6/2014 = 0.0044

0.0044

Coefficient of coincidence = 0.0044/0.0109= 0.40

Recombination interference is given by

1- C.o.C

1-0.40 =

0.6

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