Final answer:
Transposons (C) are elements that can move around within the genome, increasing genetic variability by causing or reversing mutations and changing the genetic identity of cells.
Step-by-step explanation:
Genetic variability in organisms is significantly affected by transposons (C). Transposons, also known as "jumping genes," can move from one position to another within the genome. They can create or reverse mutations and alter the cell's genetic identity. This dynamic nature of transposons can increase genetic diversity within a population.
Unlike transposons, microsatellite DNA and satellite DNA represent specific sequences that are repeated within the genome and can vary in length between individuals. These repetitive sequences can be used as genetic markers, but they do not have the same impact on variability as transposons. On the other hand, heterochromatin refers to tightly packed DNA regions that are not as actively transcribed and have a structural role in the chromosome.