The constant and naturally occurring source of variation in a population is crossing over / allele recombination. This process happens during meiosis, the type of cell division that produces sex cells (sperm and egg cells). Here's why crossing over / allele recombination fits the description:
1. Crossing Over: During meiosis, homologous chromosomes exchange genetic material. This exchange is known as crossing over. It leads to new combinations of alleles (different forms of a gene) being formed, creating genetic diversity within a population.
2. Allele Recombination: When crossing over occurs, alleles are shuffled between homologous chromosomes, resulting in offspring that have a mix of genetic traits from both parents. This genetic mixing contributes to variation within a population.
In contrast, the other options provided do not represent constant and naturally occurring sources of variation in a population:
- Learned behavior: While behavior can vary within a population, it is not inherited genetically and does not contribute to genetic variation over generations.
- Asexual reproduction: In asexual reproduction, offspring are genetically identical to the parent, leading to very little genetic variation.
- Mitosis: Mitosis is a type of cell division that produces genetically identical daughter cells, so it does not introduce new genetic variation.
Therefore, crossing over / allele recombination is the key process that introduces genetic diversity and serves as a constant and natural source of variation within a population.
