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 i