Final answer:
Offspring are genetically different from their parents in sexual reproduction due to crossing-over, independent assortment during meiosis, and the random union of gametes during fertilization, leading to genetic variation.
Step-by-step explanation:
In sexual reproduction, offspring are genetically different from the parents due to several key mechanisms. Genetic variation is the hallmark of sexual reproduction, which results in offspring with unique genetic makeups. This genetic diversity arises from processes like crossing-over and independent assortment during meiosis, along with the random union of gametes during fertilization. This diversity is crucial for the survival of species as it allows them to better adapt to changing environments and avoid the pitfalls of inbreeding.