Correct Option: B. Mutation and recombination Detailed Explanation:

1. Understanding Genetic Variation:
2. Genetic variation refers to the differences in DNA sequences among individuals within a population. This variation is crucial for the process of evolution and adaptation, as it provides the raw material for natural selection to act upon.
3. Role of Mutation:
4. Definition: A mutation is a change in the DNA sequence of an organism. Mutations can occur due to errors during DNA replication, exposure to radiation, chemicals, or viruses.
5. Impact: Mutations can introduce new alleles (variations of a gene) into a population. For example, a mutation might change a gene responsible for flower color, resulting in a new color variant that was not previously present in the population.
6. Role of Recombination:
7. Definition: Recombination occurs during sexual reproduction when genetic material from two parents is combined to produce offspring. This process involves the shuffling of alleles during meiosis, particularly during the formation of gametes (sperm and egg cells).
8. Impact: Recombination increases genetic diversity by creating new combinations of alleles. For instance, if one parent has a genotype of AaBb and the other has Aabb, the offspring can inherit a variety of combinations (AABB, AABb, AaBb, Aabb, etc.), leading to a wide range of phenotypes.
9. Why Option B is Correct:
10. Both mutation and recombination are fundamental processes that directly introduce and shuffle genetic material, leading to genetic variation. Without these processes, populations would have limited genetic diversity, making them less adaptable to changing environments.

Why the Other Options are Wrong or Weaker:

• A. Environmental changes:
• While environmental changes can influence which traits are advantageous (and thus affect the survival and reproduction of individuals), they do not directly create genetic variation. Instead, they act on the existing genetic variation within a population. Environmental changes can lead to natural selection, but they do not introduce new genetic material.
• C. Natural selection:
• Natural selection is a mechanism that acts on existing genetic variation, favoring individuals with advantageous traits. It does not create genetic variation itself. Instead, it shapes the frequency of alleles in a population based on their fitness in a given environment.
• D. Migration of individuals:
• Migration (or gene flow) involves the movement of individuals between populations, which can introduce new alleles to a population. However, it does not create new genetic variation; it merely redistributes existing genetic variation. Migration can enhance genetic diversity but is not the primary source of it.

Summary:

• Genetic variation is essential for evolution and adaptation.
• Mutation introduces new alleles, while recombination shuffles existing alleles.
• Natural selection and environmental changes act on existing variation but do not create it.
• Migration can increase genetic diversity but does not generate new genetic material.

By understanding these concepts, students can appreciate the mechanisms that drive genetic diversity in populations, which is fundamental to the study of biology and evolution.