Correct Option: C. Mutations in DNA Detailed Explanation: Genetic variation is the diversity in gene frequencies among individuals within a population. This variation is crucial for the process of evolution and adaptation. Among the options provided, mutations in DNA are the primary source of genetic variation. Here’s a step-by-step breakdown of why this is the case:

1. Understanding Mutations:
2. Mutations are changes in the DNA sequence of an organism's genome. They can occur due to various factors, including errors during DNA replication, exposure to radiation, chemicals, or even viral infections.
3. There are different types of mutations, such as point mutations (single nucleotide changes), insertions, deletions, and larger chromosomal alterations.
4. Role of Mutations in Genetic Variation:
5. Mutations introduce new alleles (variations of a gene) into a population. For example, if a mutation occurs in a gene that affects fur color in a population of rabbits, this can lead to new fur colors that were not previously present.
6. These new alleles can be beneficial, neutral, or harmful. Beneficial mutations may provide an advantage in survival and reproduction, leading to their increase in frequency over generations.
7. Natural Selection and Adaptation:
8. Genetic variation is essential for natural selection, which is the process by which certain traits become more common in a population due to their advantageous effects on survival and reproduction.
9. Without mutations, there would be no new genetic material for natural selection to act upon, and populations would lack the diversity needed to adapt to changing environments.

Why Other Options Are Incorrect: A. Environmental Changes: - While environmental changes can influence which traits are favorable and thus affect the survival of individuals, they do not create genetic variation. Instead, they act on the existing genetic variation within a population. Environmental changes can lead to natural selection but do not introduce new genetic material. B. Migration of Individuals: - Migration (or gene flow) can introduce new alleles into a population from other populations, which can increase genetic diversity. However, it does not create new genetic variation; it merely redistributes existing genetic variation. Therefore, while migration is important for maintaining genetic diversity, it is not the primary source of new genetic variation. D. Availability of Resources: - The availability of resources can affect population dynamics and survival but does not directly contribute to genetic variation. Like environmental changes, resource availability influences which individuals survive and reproduce but does not create new genetic diversity. Summary of Key Points:

• Mutations are the primary source of genetic variation in a population, introducing new alleles into the gene pool.
• Natural selection acts on existing genetic variation, allowing advantageous traits to become more common.
• Migration redistributes genetic variation but does not create it, while environmental changes and resource availability influence survival but do not generate new genetic diversity.
• Understanding the role of mutations is crucial for grasping concepts of evolution and adaptation in biology.

This thorough understanding of genetic variation is essential for students preparing for exams in biology, as it forms the foundation for many concepts in genetics, evolution, and ecology.