Video Transcript
The passage provided outlines how
chromosomal abnormalities can be caused. Chromosomal abnormalities can be
caused by changes in the blank of chromosomes or a complete loss or blank of entire
chromosomes. Which word would be most
appropriate to replace the first blank? (A) Appearance, (B) bonding, (C)
replication, or (D) structure.
This question is asking us about
chromosomes and chromosomal abnormalities. So let’s take a moment to review
what a chromosome is. Inside most of our cells, we have a
nucleus which contains our DNA. This DNA is organized into 46
chromosomes that we could see here. Chromosomes are numbered from one
to 22, with chromosome one being the largest and chromosome 22 being the smallest,
while chromosomes X and Y are sometimes called our sex chromosomes because they
determine our biological sex.
We have two copies of each
chromosome. One comes from our biological
father and the other comes from our biological mother. So, in total, we have 23 pairs of
chromosomes for a total of 46 chromosomes. If we take a closer look at one of
these chromosomes, we can see that there are many genes within it. These genes are needed for the cell
and for us to properly function. Chromosomal abnormalities exist in
some individuals where parts of a chromosome are missing or duplicated. These kinds of structural changes
in a chromosome can impact the genetic information on it and cause problems for the
cell. Therefore, the word that is most
appropriate to replace in the first blank in this passage will be “structure.”
Now, let’s look at the second part
of this question.
Which word would be most
appropriate to replace the second blank? (A) Fusion, (B) specialization, (C)
segmentation, or (D) gain.
Besides structural changes in a
chromosome, entire chromosomes can be missing or duplicated. Some syndromes, such as Down
syndrome, are caused by an additional copy or a gain of chromosome 21. Because there’s now three copies of
this chromosome, there’s now additional copies of the genes that it contains. This additional genetic information
can cause problems for the cell that are manifested as Down syndrome. Therefore, the word that’s most
appropriate to replace the second blank is “gain.”
Therefore the passage now correctly
reads “Chromosomal abnormalities can be caused by changes in the structure of
chromosomes or complete loss or gain of entire chromosomes.”
