Question

The allele "D" would be cleaved twice by EcoRI, resulting 3 fragments: 839, 262, and 215 bp. The allele with the “d” would be cleaved once by EcoRI, resulting in 2 fragments: 839 and 477 bp.

a) If a plant has a genotype of DD. How many fragments do you have? And How many bands do you see on the gel electrophoresis for this sample?

b) If a plant has a genotype of Dd. How many fragments do you have? And how many bands do you see on the gel electrophoresis for this sample?

Answer 1

a. A plant with the genotype DD has two D alleles. This implies that each D allele when treated with the EcoRI restriction enzyme will give three fragments of 839, 262, 215 bp respectively. Hence, total fragments obtained will be six in number. When these restricted fragments are run on an agarose gel electrophoresis, three bands will be observed of 839, 262, and 215 bp each. This happens because two band of same size will move up to same distance on the gel during electrophoresis, hence the two fragments of same size will appear as a single band on the gel.

b. A plant with teh genotype Dd has two alleles: D and d. Three fragment of DNA will be obtained in the case of D allele: 839, 262, 215 bp size, while two fragments will be obtained for d allele: 839 and 477 bp. When the fragments are run on the gel through electrophoresis, the two fragments of 839 bp will give a single band, while three other bands will be observed for 477, 262, and 215 bp fragments. Hence, total number of fragments of DNA are five in number while the bands in gel are four.