The ultimate source of organic variation is Mutation.

Explanation:
Mutation is the ultimate source of organic variation. It is a permanent change in the DNA sequence of an organism's genome. Mutations can occur spontaneously or can be induced by environmental factors such as radiation or exposure to certain chemicals.

Types of Mutations:
1. Point Mutations: These are small-scale mutations that involve changes in a single nucleotide base pair of the DNA. Point mutations can be further classified into three types:
- Substitution: In substitution, one nucleotide is replaced by another.
- Insertion: In insertion, an extra nucleotide is added to the DNA sequence.
- Deletion: In deletion, a nucleotide is removed from the DNA sequence.

2. Chromosomal Mutations: These are large-scale mutations that involve changes in the structure or number of chromosomes. Chromosomal mutations can be further classified into four types:
- Duplication: In duplication, a segment of the chromosome is duplicated, resulting in extra genetic material.
- Deletion: In deletion, a segment of the chromosome is lost, resulting in the loss of genetic material.
- Inversion: In inversion, a segment of the chromosome is reversed in orientation.
- Translocation: In translocation, a segment of one chromosome breaks off and attaches to another chromosome.

Importance of Mutation:
1. Genetic Diversity: Mutation is responsible for introducing new genetic variations in a population. This genetic diversity is essential for the survival and adaptation of organisms to changing environments.
2. Evolution: Mutations provide the raw material for natural selection and evolution. Beneficial mutations can increase an organism's fitness and likelihood of survival, while harmful mutations are selected against.
3. Genetic Disorders: Mutations can also lead to genetic disorders or diseases. Some mutations can disrupt the normal functioning of genes, leading to abnormal traits or health conditions.

Conclusion:
In conclusion, mutation is the ultimate source of organic variation. It introduces new genetic variations in a population, which is necessary for adaptation, evolution, and the survival of organisms in changing environments.