Within and between populations there is genetic variation, or variations in individuals' genetic makeup. This variation allows for natural selection and can sometimes be caused by mutations within a population.
Genetic variation is a term used in biology classes a lot and it actually refers to two different things depending on which level you're talking about.
Genetic variation means that when you're comparing individuals within the same population or if you're comparing two different populations, you'll see differences in their genes.
Now if you're talking about differences at the individual level, that means if you look at the same gene location or locus as scientists like to say, you may see differences in the DNA sequence. For example if we take a look at this person's DNA, maybe they have the sequence attc and so on and so forth while somebody else has this one spot a different base. So they have guanine cytosin which indicates a variation. Now that's looking at the DNA sequencing.
You can also compare individuals and look at their versions of the gene or allele that they have. For example, my friend Danielle when she sticks out her tongue and attempts to roll it, she can't. I on the other hand have the allele for the tongue rolling gene so I can. So that's variation within two individuals who are members of the same population.
Now between different populations, between two different ethnic groups, sometimes you'll see differences in the frequency of any one particular allele. And so if my friend Danny comes in, now he and I share a lot of similarities. We're both male unlike me and Danielle. But if you compare our skin tone, he's got a slightly darker skin tone than mine. So that's an example of a genetic variation between different ethnic groups. That's genetic variation.