Humans have many “good bacteria" living along their digestive tract. Not all of the food that humans eat is fully digested. The "good bacteria" feed on the undigested food. This helps the bacteria to get
nutrients and helps the human with the digestive process. What type of symbiotic relationship does this
relationship describe?

It would a Mutualism relationship

Explanation:

Because both humans and bacteria are benefiting from each other.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).