The simplest type of variation in a genome sequence is a single nucleotide change called a(n)

Single nucleotide polymorphism

Explanation:

Single nucleotide polymorphism is a genetic term that refers to the simplest type of variation in a genome sequence resulting in a single nucleotide change. In other words the single nucleotide polymorphism causes a variation in the DNA nitrogen base sequence, ie this variation can affect an adenine (A), thymine (T), cytosine (C) or guanine (G), generating a change in the nucleotide and interfering with the genome of the individual.

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igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.