Video Transcript
Karyotypes are images of a person’s
chromosomes that can be used to determine chromosomal abnormalities. Which syndrome is likely to be
caused by the chromosomal abnormality shown in the karyotype provided? (A) Klinefelter syndrome, (B)
Turner syndrome, or (C) Down syndrome.
Karyotypes, like the one shown
here, depict all the chromosomes found in a particular cell of a person. In a typical body cell, we would
expect to see 46 chromosomes, arranged in 23 pairs. 22 of these pairs are autosomes,
which means they have nothing to do with determining biological sex. The final pair are the sex
chromosomes, X and Y, which are responsible for determining whether a person is
biologically male or female. If someone has two X chromosomes,
they are biologically female. And if they have one X chromosome
and one Y chromosome, they are biologically male. In a sex cell, which is also known
as a gamete, we would expect to see just 23 chromosomes.
Now let’s look at the three
syndromes given in the question and see how each one would affect the typical
karyotype. Klinefelter syndrome is a condition
which only affects biological males. It’s caused by an individual having
an additional X chromosome. In other words, they have two X
chromosomes and one Y chromosome. The main features of Klinefelter
syndrome are having small, poorly functioning genitals and being infertile.
By contrast, Turner syndrome only
affects biological females. It’s caused by an individual only
having one normal X chromosome, rather than the usual two. Turner syndrome is characterized by
having a short stature, impaired reproductive development, and being infertile.
Finally, Down syndrome is caused by
the presence of an extra copy of chromosome 21. This means affected individuals
have three copies of chromosome 21, rather than the usual two. Because Down syndrome does not
involve a change to the sex chromosomes, it can affect both biological males and
females. The main features of Down syndrome
are impaired growth, intellectual disability, and characteristic facial
features.
If we now return to the karyotype
provided in the question, we can see that this individual only possesses one copy of
the X chromosome. We can therefore deduce that the
correct answer is (B). The chromosomal abnormality shown
in the karyotype provided is likely to cause Turner syndrome.
