What is the source of Variation?
 A. Mutation
 B. Recombination
 C. Deletion
 D. All of the above

Hint: Variation can be defined as any difference present between cells, individuals or in groups of organisms of any species beacuse of genotypic variation or effect of environmental factors on the expression phenotypic variation. For a given population, there are three sources of variation: mutation, recombination and immigration of genes or deletion.

Step by step answer:A mutation is a change that occurs in our DNA sequence, either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke. Mutation can occur during DNA replication if errors are made and not corrected in time. Mutation can be inherited from both one or both parents. They are present in the egg or sperm cells.
Recombination of genes occurs by the exchange of genetic materials between different organisms which lead to production of offspring with combinations of traits that differ from those found in either plant.
A deletion mutation is a mistake in the DNA replication process which removes nucleotides from the genome. A deletion mutation can remove a single nucleotide, or entire sequence of nucleotides.

Hence, the correct answer is option (D). All of the above.

Note: Variations are of two types: Continuous and discontinuous variation. Characteristics showing continuous variation vary in a general way, with a broad range, and many intermediate values.