Concept:Genetic variation in sexually reproducing animals arises because offspring inherit a unique combination of genes from both parents.
Explanation:During sexual reproduction, male and female gametes (sperm and egg) fuse during fertilisation.
Each gamete is produced by meiosis, which introduces genetic recombination (e.g., crossing over) and random assortment.
The fusion of two genetically different gametes creates a zygote with a novel set of chromosomes from both parents.
This inheritance from two parents generates variation in traits, helping species adapt to changing environments.
Option A is incorrect because gametes are formed by meiosis, not mitosis – mitosis produces identical cells, not variation.
Option B is false because the location of fertilisation (internal or external) does not directly cause genetic variation.
Option D is wrong because only one parent involved is asexual reproduction, which yields clones, not variation.
Thus, the key factor ensuring genetic variation is that offspring receive genes from both parents.
Answer:Offspring receive genes from both parents (Option C).