Video Transcript
The figure shows a chromosome about
to go through mitosis. What is structure X? And what is structure Y?
Let’s look at this diagram we’re
provided with. It’s a diagram of a chromosome
about to go through mitosis, or cell division. We know that chromosomes consist of
condensed DNA and that DNA replicates before cell division. So what we have here is a
replicated chromosome or a chromosome that consists of replicated DNA. What that means is that this part
of the chromosome is what we call a single chromatid, and the other side is
basically a copy of it, which we call its sister chromatid. This can go the other way as
well. There is not one side that’s
specifically defined as the original chromatid and the other as the copy. Both sides contain the same
information and are essentially copies of each other, and each side is a
chromatid. And the two chromatids in a
replicated chromosome are sister chromatids of each other.
These two sister chromatids in a
replicated chromosome are held together or attached to each other by a centromere in
the middle. During cell division, the spindle
fibers that move chromosomes around the cell and, for example, line them up in the
middle of the cell during one step of cell division are attached to the centromeres
of the chromosomes. But we do not see any spindle
fibers in this diagram, which makes sense because the spindle fibers attach during
mitosis, and this chromosome is apparently just preparing for mitosis.
So instead in this diagram, all we
see are the two chromatids, which we can also call sister chromatids, and the
centromere in the middle, which attaches the two chromatids to each other. So let’s look back at our
questions. What is structure X? X is pointing to the centromere
that holds the two chromatids together. And what is structure Y? Y is pointing to a chromatid.
