Video Transcript
Which of the following best describes an allele? (A) The interaction of DNA with the environment. (B) A section of DNA that codes for a protein. (C) Different forms of the same gene. (D) All the DNA within an organism. (E) Similar forms of different genes.
The genome is all the genetic information of an organism and is necessary to make me,
you, and the figure shown here. Our DNA is located in the nucleus of our cells and is organized into structures
called chromosomes. Let’s zoom in on this nucleus so we can get a better look.
We have 46 chromosomes, or 23 pairs of chromosomes, in most of our cells. We get one copy from our biological father and the other from our biological
mother. They’re numbered from one to 22, with chromosome one being the largest and chromosome
22 being the smallest. The 23rd chromosome pair is the sex chromosomes. These are called the sex chromosomes because they determine our biological sex. Having a single copy of the X chromosome and a single copy of the Y chromosome
results in a biological male, while having two copies of the X chromosome results in
a biological female.
Now, in order to answer this question and learn what an allele is, let’s focus on the
circled chromosome pair and remove these other chromosomes so we have more room to
work with.
So here are the two copies of chromosome 16 side by side. The DNA in these chromosomes is highly compacted. So let’s unravel them so we can see this in more detail. Here, we can see how DNA is wrapped tightly around special proteins called
histones. This is how DNA is so highly compacted in chromosomes.
Some sections of DNA contain the information for producing certain functional units,
like proteins. These are called genes. These genes will be scattered throughout the chromosome. And here, you can see a few of them colored as orange bands. These genes are in the same positions on each chromosome because they’re the
same. So we might have two copies of each gene, but they might be slightly different from
the other copy.
For example, one gene version might provide the instructions for blue eyes, while the
other provides instructions for green eyes. This is the same gene, but we got different versions of it from our biological father
or mother. We call these different versions of the same gene alleles.
Therefore, the option that best describes an allele is given by answer choice (C),
different forms of the same gene.
