Well, we can definitely calculate genotype frequencies always,

when we have the counts of the different genotypes.

So let's assume in this case that every individual is a diploid there,

they have two copies of all their genomes.

So we can literally just get this by counting.

So here's a population, and its AA, Aa, aa's.

There's ten individuals in this population.

One, two, three, four, five, six, seven, eight, nine, ten.

The frequency of AA will be it's abundance.

Which there's only one right here.

So it'd be one out of ten or 0.1.

So same as 10%.

Frequency of Aa's.

There are one, two, three, four, five, six.

Out of ten.

Or 0.6.

For aa, it's the ones that are not circled, it's three out of ten.

So .3.

So you add up these three numbers, and again, it adds up to 100%.

As we expect.

What about allele frequencies?

Well, there's two ways we can actually do this.

The most obvious way, which is not necessarily the better way,

is to literally just count the big A's, and the little a's, in this group.

So we could look at this and see well there's 20 total alleles here.

They're attached together as genotypes but they are 20 alleles.

How many big As are there.

One two three four five six seven eight.

Eight big A's out of 20.

So how many little a's are there.

It obviously must be twelve.

If 8 out of 20 are 0.4 "A"s then 12 out of 20 are 0.6 "a"s.

Again, this adds up to 100%.

The better way, when working with a large number of genotypes, rather than counting

than individual alleles like this, is to look at the genotype frequencies.

We can say that we know that "AA"s are completely made up of the "A" allele.

So the frequency of big A would be the frequency of AA and

half the frequency of Aa.

So these are the numbers we used from the previous slide.

Remember that our frequency of AA is 0.1.

Our frequency of Aa is 0.6 from the previous slide.

We add up 0.1 plus 1/2 of 0.6, which would be 0.3, which comes to 0.4.

It's exactly the same as what we saw up here.

Similarly we can say the frequency of aa or 0.3 + 1/2 0.6.

So that's 0.3 + 0.3 and that's 0.6.

Exactly what we see over here.

And again these add up to 100%.

This is what we expect.