Video Transcript
Which of the following statements
is not true about DNA fingerprinting? (A) It is possible to examine the
genetic variation in other living things using DNA fingerprinting. (B) It is possible to determine the
order of nucleotides within certain genes on chromosomes using DNA
fingerprinting. (C) It is possible to establish the
identity of dead bodies using DNA fingerprinting. (D) It is possible to identify the
father of a person using DNA fingerprinting.
This question asks us about DNA
fingerprinting, which has many important applications. It is a technology that takes
advantage of the unique sequence of nucleotides present within the cells of each
individual.
You may recall that all living
organisms contain DNA. This DNA is made up of repeating
subunits called nucleotides that contain different nitrogenous bases. These can be guanine, cytosine,
adenine, or thymine. In humans, each cell contains
billions of these nucleotides. And the sequence of these
nucleotides is 99.9 percent the same between two individuals. This amounts to about one
nucleotide that’s different for every 1000 nucleotides in a person’s DNA. And since there’s billions of
nucleotides in a person’s cells, this represents millions of differences.
Let’s represent some of these
differences as black dots in the DNA of person B. Here you can see one nucleotide
from person A is an adenine, while this is a cytosine in person B. In order to see these differences,
we can use special enzymes called restriction enzymes that can cut DNA at specific
nucleotide sequences. Because restriction enzymes cut
DNA, we’ll represent one as a pair of scissors. Let’s say this restriction enzyme
only cuts the DNA sequence GAATTC. The DNA in person A has this
sequence at this particular site, so it will be cut by the restriction enzyme. However, person B has a different
nucleotide at this position. So the restriction enzyme won’t cut
the DNA at that point.
Because of the differences in these
two sequences, this results in different cutting patterns throughout the DNA of
person A and person B. Some cuts are the same, while some
are different. These cuts produce fragments of
DNA. And because there are different
cutting patterns between these DNA sequences, there will be differently sized
fragments. Using a special technique called
gel electrophoresis, these fragments can be arranged by their size in a gel and
photographed. This pattern of fragments that we
see in the gel is unique to each individual and is why we call this a DNA
fingerprint.
Now let’s go through the different
answer options to determine which is not true about DNA fingerprinting. In answer choice (A), DNA
fingerprinting can be used to identify genetic variation. Unless the two organisms were
identical, their respective DNA will be cut differently by restriction enzymes and
produce unique DNA fingerprints. Since this is a correct statement
and we’re looking for a statement that is not true, this answer is incorrect.
In answer choice (B), we cannot
determine the order of nucleotides, or the sequence, from DNA fingerprinting. We’re only seeing differently sized
fragments, which corresponds to differences in DNA sequence. So this is not a correct statement
and is therefore a correct answer choice.
Let’s look at the last two
statements before making our final choice. In answer choice (C), it is
possible to identify dead bodies using DNA fingerprinting because these fingerprints
are unique to individuals. So this answer choice is
incorrect. In answer choice (D), it is
possible to identify the father of a person using DNA fingerprinting because about
half of the DNA sequence would be the same between the father and child, which would
produce similar DNA fingerprints that wouldn’t arise due to chance alone. So this is incorrect.
Therefore, the statement that is
not true regarding DNA fingerprinting is given by answer choice (B). It is possible to determine the
order of nucleotides within certain genes on chromosomes using DNA
fingerprinting.
