Question

A group of six students has taken samples of their own cheek cells, purified the DNA, and used a restriction enzyme known to cut at zero, one, or two sites in a particular gene of interest.
Analysis of the data obtained shows that two students each have two fragments, two students each have three fragments, and two students each have one only. What does this demonstrate?
A. The two students who have two fragments have two restriction sites within this gene.
B. Each of these students is heterozygous for this gene.
C. The students with three fragments are said to have "fragile sites."
D. The two students who have two fragments have one restriction site in this region.
E. Each pair of students has a different gene for this function.

Answer 1

Answer:

D. The two students who have two fragments have one restriction site in this region.

Explanation:

The DNA samples from the cheek cells were subjected to digestion with a restriction enzyme. This enzyme is an endonuclease and cuts the DNA at a specific sequence only. This sequence is called a restriction site. If the restriction site is not present in the sample DNA, the restriction enzyme cannot cut it. The presence of one restriction site in the sample DNA would cut it into two DNA fragments.

Similarly, the presence of two restriction sites in each DNA molecule would obtain a total of three DNA fragments per DNA molecule.