A karyotype is an image of a
person’s chromosomes that can be used to determine chromosomal abnormalities. Which syndrome will likely be
developed as a result of the chromosomal abnormality shown in the karyotype
provided? (A) Turner syndrome, (B) Down
syndrome, or (C) Klinefelter syndrome.
This question asks us about a
syndrome resulting from a chromosomal abnormality which occurs when an individual
inherits a different number of chromosomes than usual. Normally, an individual will gain
one copy of each chromosome from the biological mother and one copy from the
biological father. In a karyotype, we arrange these
chromosomes in order by height.
The matching chromosomes from each
parent are called homologous chromosomes. During gamete or sex cell
formation, an individual’s chromosomes are divided in half. Typical human body cells will
contain 46 chromosomes, while sex cells will only possess 23. Of these chromosomes, 22 will be
autosomes that once fertilization occurs will make up one-half of a homologous pair,
while one will be a sex chromosome.
Sex chromosomes are either X or Y,
and they contain genes specific for sexual development. When these gametes come together
during fertilization to form a new individual, there will be 46 chromosomes in
total. Either a male or a female will be
produced. Sometimes the process of sex cell
formation will incorrectly separate the chromosomes so that they aren’t divided
evenly. If this sex cell is involved in the
process of fertilization, or the joining of a sperm and an egg, it can result in an
offspring with a chromosomal abnormality.
Now, let’s take a look at the
karyotype in our question. You can see that the individual
possesses three copies of chromosome 21. But normal body cells should only
contain two copies of each chromosome: one from the biological mother and one from
the biological father. These chromosomes must have been
incorrectly split during sex cell formation, resulting in a trisomy, or three
In our question, the individual
contains a trisomy 21, which results in a condition called Down syndrome. Characteristics of Down syndrome
include heart defects, a flattened facial profile, and short stature. In addition, these individuals may
develop intellectual disabilities.
Now that we have reviewed
chromosomes and conditions that can develop from their incorrect separation during
gamete development, we should be able to answer our question correctly. We’re asked which syndrome will
likely develop as a result of the chromosomal abnormality shown in the karyotype
provided. The correct answer is (B), Down