question_answer

The restriction fragment shown below contains a gene whose recessive allele is lethal. The normal allele has restriction sites for restriction enzyme pst I at sites I and II. The recessive allele lacks restriction sites I. An individual who had a sister with the lethal trait is being tested to determine if he is a carrier of that lethal trait.

Which of the band patterns would be produced on a gel if he is a carrier?

A)

B)

C)

D)

Correct Answer: D

Solution :

· Normal allele · · Recessive allele · · If an individual is a carrier he will have 1 copy of the normal allele and 1 copy of the recessive allele. When digested with restriction enzyme pst I, there will be 5 restriction fragments formed · · Gel electrophoresis is used for separating the mixture of fragments obtained through a gel in an electrical field. The negatively charged DNA molecules migrate toward the positive electrode at a rate inversely proportional to their length. Thus, the largest fragment will be closest to the negative electrode, while the 3 smaller fragments which are similar in length are closer to the positive electrode.