What is common between these two pictures? Describe it in short.

Eustachian Tube

Explanation:

Eustachian tube is the structure that connects the throat to middle ear. It performs an important role in the balancing of air pressure across the both sides and prevent from fluids building up in the ear.

Hope this helped!

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).

not sure if this is what you'r looking for eubacteria and archaebacteria