Retrotransposons are a type of transposable element, or transposon. These segments of DNA can duplicate and insert themselves into new locations in the genome. For example, the Alu sequence is about 300 bases long, and it is the most abundant retrotransposon in primate genomes. In fact, it makes up approximately 15% of the human genome.
Choose the description below that best completes the following statement in describing what ways the Alu sequence can affect the size of the human genome.
The Alu sequence_______.

A. can increase the size of the human genome because it adds 300 bases to the genome each time it is duplicated
B. can decrease the size of the human genome because the element is always inserted into an intron so it will be spliced from the human genome
C. cannot influence the human genome because the human genome cannot blend with any of the other primate genomes
D. can either increase or decrease the size of the human genome because transposable element insertion mutations are coupled with telomere shortening

The human's genome is comprised of all the nucleotides present in the cells nucleus, including exons, introns and non coding sequences. Therefore, independently of where are located, retrotransposons can increase the size of the human genome. In the case of the Alu sequence it adds 300 bases to the genome each time it is duplicated, which as stated makes up approximately 15% of the human genome.