Chickens do not need teeth. It is a muscular part of the stomach and uses grit small, hard particles of pebbles or sand to grind grains and fiber into smaller, more digestible, particles. From the gizzard, food passes into the small intestine
A stimulus is a change in an organism's surrounding that causes it to react.
I think it would most likely be passed along when there are more than one mutations in a gene.
