Which of the following contribute(s) to the variation in offspring produced by sexual reproduction?
a. crossing over
b. mutation
c. independent assortment
d. random fertilization
e. all of the above

The correct answer is E. All of the above

Explanation:

Variation in offspring can be contributed by many different events that change the DNA sequence in gametic cells. These events are crossing over, mutation, independent assortment, and random fertilization.

During the gamete formation, the different genes are assorted independently from the other gametes which results in forming various possible combinations of genes in a gamete increasing the genetic variation.

Crossing over occurs during meiosis between the homologous chromosome that results in exchange of genetic material that brings genetic variation in gametes. During random fertilization, the two gametes fuse and genetic material of two different individual comes to make an offspring which forms a genetical different offspring.

Mutation in the gametic cell is transferred to the offspring during fertilization. Therefore all contributes to variation in offspring produced by sexual reproduction.