Commensalism :)
in case when bacteria and human, both are benifited.
interlocking calcium carbonate plates is the answer.
The answer is the
population size. The chance has a role
in determining whether a given individual survives and reproduces and the
alleles in the offspring are a sample of those in the parents. it is the change
in the frequency of an existing gene variant (allele) in a population due to
random sampling of organisms. Genetic Drift or another term for allelic drift
or the Sewall Wright effect.
This can happen because you have recessive and dominant characteristics passed down. So you can get a totally different chromosome that doesn't come from your parents because your grandparents may have had it or great grand parents, the line keeps going .