In as much detail as possible, explain what crossing over is, including when it occurs, why it
occurs, and how it contributes to genetic variation: *

Explanation:

Crossing over is an important section of the normal segregation of the chromosomes in case of the meiosis. Crossing over happens due to the genetic variations, as the genetic materials gets alter at the time of crossing over. The chromatids that are bind together with the help of the centromere do not remain similar in this case. Crossing over gives rise to variation because the alternation takes place between the nonidentical chromatids having different characteristics or traits. Sometimes gives rise to completely new trait which is not present in both the parents this condition makes the . genetic diversity.

digestion

it excretes wastes