Video Transcript
The paternity of a child is in dispute. A DNA fingerprint is constructed for the child, their mother, and their potential
father. True or False: Based on the information in the diagram provided, the man is the
biological father of this child.
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. Our total amount of DNA, or our genome, is billions of nucleotides. So this 0.1 percent difference actually represents millions of nucleotides that are
different between individuals.
In order to see these differences, we can use special enzymes called restriction
enzymes that can cut DNA at specific nucleotide sequences. Because of the differences in the two sequences, this results in different cutting
patterns throughout the DNA of person A and person B. 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 we see in the gel is unique to each individual and is why
we call this a DNA fingerprint.
Now that we understand how a DNA fingerprint can be constructed, let’s try to answer
our question. We are shown three different DNA fingerprints and are asked if the father is related
to the child. To determine this, we need to compare the different bands between the child and
father and look for similarities. Remember, when we are conceived, we get half of our DNA from our biological mother
and the other half from our biological father. So the child’s DNA fingerprint should be a combination of both the mother and
father.
Let’s start by comparing the child and mother before we look at the father. Here, we can see two bands that are shared between the mother and child. And here are the other bands that are shared between the mother and child. Note that we are not questioning the maternity of the child, so we know that these
bands were inherited from the mother.
The remaining bands in the child are shown in blue. Notice how none of these bands are represented in the potential father’s DNA
fingerprint. This means the child must have inherited them from someone else and this potential
father is not the biological father.
Therefore, if we go back to this statement in the question “True or False: Based on
the information in the diagram provided, the man is the biological father of this
child,” the correct answer is false.
