Understanding Genetic Variation Sources

Genetic variation is crucial for the adaptation and evolution of species. In sexually reproducing animals, this variation arises primarily from the unique combination of genes inherited from parents.

Key Factor: Parental Gene Contribution

The core principle of sexual reproduction involves the fusion of gametes (sperm and egg) from two parents. Each gamete carries half the genetic information of its parent.

• When fertilization occurs, the resulting offspring inherits a mix of genes from both the mother and the father.
• This combination creates a novel genetic makeup in the offspring, distinct from either parent.
• This shuffling and recombination of parental alleles is the fundamental reason for genetic variation among offspring in sexually reproducing populations.

Therefore, the statement "Offspring receive genes from both parents" directly ensures genetic variation.

Evaluating Other Options

• Fertilisation occurs inside the body: Internal fertilization is a mode of reproduction but doesn't inherently guarantee genetic variation. The variation comes from the genetic material involved, not the location of fertilization.
• Gametes are formed by mitosis: This is incorrect. In sexual reproduction, gametes are formed through meiosis, a process involving genetic recombination (crossing over) and independent assortment, which actively generates variation. Mitosis produces genetically identical cells.
• Only one parent is involved: This describes asexual reproduction, which typically produces offspring genetically identical (or very similar) to the single parent, resulting in low genetic variation.

Based on this analysis, the inheritance of genes from two parents is the primary mechanism ensuring genetic variation.