Question

The map below illustrates three alleles in a genome segment. The alleles differ in the number and location of restriction sequences. Restriction digestion and Southern blotting with the molecular probe whose hybridization location is indicated results in detection of a single DNA band for each allele. a. List the size of the DNA bands that would be detected for each of the following genotypes: D^2 D^2: D^2 D^3: D^3D^3: b. Restriction-digested DNA from two organisms is analyzed by Southern blotting. Restriction fragments of 2.0 and 3.5 kb are observed on the Southern blot of one organism, and bands of 2.0 and 3.0 kb are observed for the other. What are the genotypes of these organisms? Genotype of organism with 2.0 and 3.5: Genotype of organism with 2.0 and 3.0: c. Restriction-digested DNA from 3 organisms is analyzed by Southern blotting using a DIFFERENT probe than the one shown in the figure. Show where the probe binds on the figure above and genotype each of the individuals below: Organism 1: 1.5, 2.0: Organism 2: 1.5, 2.0, 3.0 Organism 3: 1.5, 3.5, 3.0:

Answer 1

a.

D²D² – homozygotes. The probe detection site is located in 3.0 kb fragment.

D²D³ heterozygote: The probe detection site is 3.0 kb fragement for D2 allele and 3.5 kb fragment for D3 allele.

D³D³ homozygote: The probe detection site is 3.5 kb fragment for both the alleles.

b.

The two kb fragment is from D1 allele, and the 3.5 kb fragment is from D³ allele. Hence the 2.0 and 3.5 kb allele corresponds to heterozygous D¹D³ genotype.

The 2.0 kb and 3.0 kb fragments correspond to D¹ and D² alleles respectively. Hence the genotype is D¹D².

c.

The location of the probe is shown in the picture given below:

Organism 1: D¹D¹ homozygoute

Organism 2: D¹D² heterozygote

Organism 3: D²D³ heterozygote