Population genetics tries to know mostly about the consequences of genetic change in a population. We will first try to explain some important concepts, then to explain the Hardy-Weinberg equilibrium and then to introduce mutations,recombinations into the population. You will see also this is important in the evolution theory
You probably know most of these things, but it easy to have an overview
A gene is a heritable coded unit. Three words appear in it. So it is most easy to explain these. Heritable means a gene is passed from one generation to the other generation. The coded means it is a code which will be copied first (transcription)and later on translated (which is called uh ... translation). The unit means there is no smaller thing that will be a functional or working code (though splicing and post-translational events can make things more complicated).
A locus is the physical place of a gene on the chromosome.
An allele is one variant of a gene. So if you got a gene which codes for the colour of your eyes, you can have an allele which codes for blue eyes while your best friend can have an allele for brown eyes. Alleles are also on the same locus.
A population is a group of organisms which belong to the same species and can be regarded as an entity. This is a vague definition. One can consider the population of worms in a local forest, but one can also consider the population of worms in Yellowstone. So the place where these organisms live is defined by the writer himself.
5.Ideal or panmictic population
It is defined as a population in which each individual has the an equal chance to get children from every individual of the other sex. So mating is called random. Of course this is a pure theoretical concept, but as we will later on see it is a useful concept.
The Hardy-Weinberg equilibrium
This concept assumes there is no evolution at all. It is very easy to use this and then introduce the effects of a mutations and recombination etc.
Suppose now you have one gene with two alleles A and a. Their relative frequencies are p and q and p+q = 1
|A (p)||a (q)|
|Males||A (p)||AA (p2)||Aa (pq)|
|a (q)||Aa (pq)||aa (q2)|