Chapter 21, Problem 40A

Summary Introduction

To determine:

The sample by which scientists may know which plant contained the introns using PCR.

Introduction:

Polymerase chain reaction is a technique used to make millions of copies of a specific region of DNA fragment. It can replicate DNA outside the living organisms. The technique is highly sensitive. It can detect even a single DNA molecule in a sample. PCR is an important tool for molecular biologists as it helps in diagnosis of infectious diseases.

Explanation of Solution

The three steps of PCR are:

1. The DNA fragment, DNA polymerase, four nucleotides and two DNA primers are heated in a tube. The primers are used as starting points for DNA synthesis.

2. The two strands of DNA fragment separate due to heating and on cooling the primers bind to each strand of template DNA.

3. DNA polymerase then incorporates the correct nucleotides between the two primers to form new DNA molecules.

After running PCR on intron containing gene, scientist can go for gel electrophoresis. In gel electrophoresis, sample of intron containing gene (standard gene) and DNA sample of different plants can be made run through the gel. Then, when the complete sample has run through the gel, then compare the DNA fragments. If the DNA sample of any plant has same profile like standard DNA sample, then this means that plant’s gene contain introns.