Hardy-Weinberg principle?

A hypothetical one.  Hardy-Weinburg equillibrium is not possible for actual living populations to achieve.  There are a number of assumptions built into the theory which make it impossible for real-life populations to be in HWE.

In order for a population to be in hardy-weinberg equilibrium it must posess these five traits
1. no mutation pressure
2. no immegration or emmigration
3. no natural selection, or selection pressure
4. population must be large
5. reproduction must be random
if these 5 condition are met then p and q remain constant

Hardy-Weinberg describes the allele frequencies of a non-evolving population. Thus, for a population to be in hardy-weinberg equlibrium, there are five conditions:

1. A very large population size. A small population size will be highly suceptible to genetic drift, the change in allele frequencies purely due to chance.

2. No migration: no gene flow, or the transfer of alleles between populations due to movement of individuals between populations, can occur

3. No mutations
4. Random mating: sexual selection will not be a random mixing of gametes needed for Hardy weinberg equilibrium
5. No natural selection: for obvious reasons, natural selection will alter allele frequencies that deviate from Hardy-weinberg.

Thus, no real population can truly be described using Hardy-Weinberg, because no populations satisfy these conditions. In essence, populations which deviate from Hardy-weinberg are evolving, and we know all populations constantly evolve.

one controlled in a laboratory, it can not be found in nature