Microevolution and Hardy Weinberg Equilibrium

[kumara]

Why microevolution could not occur in a population at Hardy Weinberg Equilibrium.?

[wbla3335]

Well, think about the meaning of the terms in your question. Evolution means change, and equilibrium means no change. HWE is a theoretical concept that doesn't actually exist in any real population. In real populations, new alleles constantly arise through mutation, recombination, gene flow, etc., and allele frequencies constantly change through selection and drift. HWE assumes random mating, which can but usually does not occur. If you can imagine a population that satisfies all the conditions of HWE, with no changes occurring, either in the organisms or the environment in which they live, then there can be no change in allele frequencies - no evolution.

[AFJ]

wbla... wrote
In real populations, new alleles constantly arise through mutation....

Wbla,

How would you define "mutation" in populations? Are you talking about known mutations?

[wbla3335]

How would you define "mutation" in populations? Are you talking about known mutations?

No. Known mutations, just by the fact that they are known, do not make new alleles. My definition of "mutation" is the standard one: a point mutation, an insertion or deletion, inversion, etc. These mutations, of course, occur once in a single individual of a population (and it must occur in a germ cell). If that individual fails to reproduce, then the mutation is gone when the individual dies. If that individual does reproduce, then the mutation has a chance of increasing its frequency in the population. It may quickly disappear if it is harmful, or simply by genetic drift. If it helps in some small (or rarely large) way for an individual to survive and reproduce, then it may increase in frequency. If a mutation is neither harmful nor helpful, then it may either stay or disappear.

[Darby]

Hardy and Weinberg, by imagining the conditions under which a population would NOT evolve, threw a light on the mechanisms of change, including some parameters that hadn't been considered much. It's not supposed to be a real situation.