QUESTION 1:

An Hfr strain is used to map three genes in an interrupted matingexperiment. The cross is Hfr/a+ b+ c+ rif X F-/a- b- c- rifr. (Nomap order is implied in the listing of the alleles; rifr isresistance to the antibiotic rifampicin.) The a+ gene is requiredfor the biosynthesis of nutrient A, the b+ gene for nutrient B, andthe c+ for nutrient C. The minus alleles are auxotrophs for thesenutrients. The cross is initiated at time = 0, and at varioustimes, the mating mixture is plated on three types of medium. Eachplate contains minimal medium (MM) plus rifampicin plus specificsupplements that are indicated in the following table. )The resultsfor each time interval are shown as the number of colonies growingon each plate.)

Time of Interruption

Supplements Added to MM 5 min 10 min 15 min 20 min

Nutrients A and B 0 0 4 21

Nutrients B and C 0 5 23 40

Nutrients A and C 4 25 60 82

Based on these data, determine the approximate location on thechromosomes of the a, b and c, genes relative to one another and tothe F factor.

Choose one answer.

1. c a b F

2. a b c F

3. F a b c

4. F b a c

5. b a c F

QUESTION 2:

Two Theoretical genetic strains of a virus (a- b- c- and a+ b+c+)were used to simultaneously infect a culture of host bacteria.Of the 10,000 plaques scored, the following genotypes wereobserved. Determine the genetic map of these three genes on theviral chromosome. Decide whether interference was positive ornegative.

a+ b+ c+ 4100 a- b+ c- 160

a- b- c- 3990 a+ b- c+ 140

a+ b- c- 740 a- b- c+ 90

a- b+ c+ 670 a+ b+ c- 110

Choose one answer.

1. a b c, positive

2. b a c, negative

3. c a b, positive

4. a c b, negative

5. a c b, positive