Video Transcript
What is meant by repetitive
DNA? (A) Consecutive sequences of DNA
that repeat themselves and that are found throughout the genome. (B) Copies of the genome repeated
in a cell and found throughout the organism. (C) Genes that are repeated in
several copies throughout the genome. (D) Nucleotides that are used more
than once within DNA.
DNA, or deoxyribonucleic acid, is
the molecule that carries the genetic information in all living organisms. A molecule of DNA is most commonly
composed of two strands, each of which is a chain of individual units called
nucleotides. We can see these different
nucleotides here and the corresponding nucleotide sequence of one of these strands
as it coils around the opposing strand.
In humans, if we look at the
complete sequence of DNA, or our genome, it’s over three billion nucleotides
long. We discovered this after sequencing
the human genome as part of the Human Genome Project, which was a worldwide effort
by multiple scientists that took over 10 years to complete.
Besides learning about the size of
the human genome, we also discovered that it contains over 20,000 protein-coding
genes, which represents about one percent of our genome. This includes sequences that code
for proteins, such as insulin or hemoglobin. The remaining 99 percent is made up
of noncoding DNA. This is a DNA sequence that doesn’t
code for proteins. These sequences can include
structural RNAs like ribosomal or rRNA or regulatory RNA like microRNAs.
However, about half of our genome
is made up of repetitive DNA sequences with no clear function. An example of this is called the
Alu element, which is a 300-base-pair-long segment of DNA that is repeated over one
million times in the human genome. In fact, about 10 percent of our
genome is made up of these repeated Alu elements.
Getting back to our question, the
option that best describes what is meant by repetitive DNA is given by answer choice
(A): consecutive sequences of DNA that repeat themselves and that are found
throughout the genome.
