Video Transcript
Fill in the blank. Chromosomal abnormalities can be caused by changes in the blank of chromosomes or a
complete loss or gain of entire chromosomes. (A) Structure, (B) bonding, (C) color, (D) replication.
This question is asking us about chromosomal abnormalities. Let’s take a moment to review how our DNA is organized as chromosomes in our
cells. In humans, we have 23 pairs of chromosomes, or 46 in total. Each pair consists of one chromosome that was contributed from our biological mother
and another that was contributed by our biological father.
Our chromosomes are arranged by size with chromosome one being the largest and
chromosome 22 being the smallest. The 23rd chromosome pair is our sex chromosomes, which determine our biological
sex. Having two copies of the X chromosome results in a biological female, while a single
copy of the X and Y chromosome results in a biological male. These chromosomes in each pair are homologous to each other, which means that the two
chromosomes are approximately the same size and contain the same genes.
In some cases, these chromosomes can be duplicated or deleted, so we have a different
number from what’s normal. For example, in Down’s syndrome, there’s an extra copy of chromosome 21. This extra copy includes all the genes that are in the other two copies of chromosome
21. So now there’s a surplus of genetic information. This can cause multiple problems in the body that are together manifested as Down’s
syndrome.
Besides the complete gain of a chromosome, the structure of a chromosome can be
affected. An example of this is in cri du chat syndrome, where a piece of chromosome five is
missing. Because this piece of chromosome five contains many important genes, when these are
deleted, this can cause the symptoms of this syndrome. One such symptom is the characteristic catlike cry of affected infants.
Getting back to our question, the option that correctly fills in the blank in the
statement “chromosomal abnormalities can be caused by changes in the blank of
chromosomes or a complete loss or gain of entire chromosomes” is given by answer
choice (A), structure.
