The genes for the normal and sickle cell anemia alleles of hemoglobin are cut with the restriction enzyme DdeI. The resulting DNA fragments were separated by gel electrophoresis, producing the gel shown in the figure below.
Why are the patterns produced by these two alleles different?
A) The normal hemoglobin gene is cut by two restriction enzymes, but the sickle cell anemia allele is cut by only one restriction enzyme.
B) The gene for the normal allele is much larger than the gene for sickle cell anemia.
C) The gene for the normal allele has a sequence recognized by DdeI, but the gene for sickle cell anemia does not.
D) The sickle cell allele has the ability to produce ligase to repair the damage done by restriction enzymes, but the normal allele does not.

Question

The genes for the normal and sickle cell anemia alleles of hemoglobin are cut with the restriction enzyme DdeI. The resulting DNA fragments were separated by gel electrophoresis, producing the gel shown in the figure below. 
Why are the patterns produced by these two alleles different?
A) The normal hemoglobin gene is cut by two restriction enzymes, but the sickle cell anemia allele is cut by only one restriction enzyme. 
B) The gene for the normal allele is much larger than the gene for sickle cell anemia. 
C) The gene for the normal allele has a sequence recognized by DdeI, but the gene for sickle cell anemia does not. 
D) The sickle cell allele has the ability to produce ligase to repair the damage done by restriction enzymes, but the normal allele does not.

Quizplus · Accepted Answer

The patterns produced by these two alleles are different because the gene for the normal allele has a DdeI recognition sequence, while the gene for sickle cell anemia does not. Therefore, the restriction enzyme DdeI will cut the normal hemoglobin gene into two fragments, but will not cut the sickle cell allele. This results in different patterns when the fragments are separated by gel electrophoresis. Choice A is incorrect because both alleles are cut by the same restriction enzyme. Choice B is incorrect because the size of the gene has no effect on the recognition sequence of the enzyme. Choice D is incorrect because neither allele has the ability to produce ligase.

The Genes for the Normal and Sickle Cell Anemia Alleles