Explain how independent assortment, crossing over, and random fertilization contribute to genetic variation in sexually reproducing organisms.

Crossing over occurs at prophase 1 of first meiotic division; at a point called CHIASMA, when they form a BIVALENT. During this  period genes are switched between non sister chromatids of homologous chromosomes; which  allow the mix up of individual parent's genetic materials leading to formation of recombinant  chromosomes.

Independent assortment of genes  takes place at meta phase 1 of meiosis.it is the lining up of homologous chromosomes randomly, from the  individual parent different  chromosomes . Basically; there are 2n different forms of lining up of homologous chromosomes at this stage.

Random fertilization increases chances of  genetic variation. Million of sperm cells with varied genetic components, fused with the ovum. the random fertilization ensure that unpredictable characteristics of the two parents are combined leading to formation of hybrid.

Explanation:

the correct answer is:

a population changes in response to a change in the environment.

several tissues working together form an organ, and several organs together make up an organisms.

the group of cell that carries out special jobs are tissue.