chapter 23. the evolution of population

Q. what are the five conditions that should follow when we use Hardy-Weinberg's equilibrium?

No migration

Large population size

No mutation

Random mating

No selection

Q. what is population?

A population is an interbreeding group of organisms (the same species) that occupies a particular area.

Q. what is genetic drift reffered to?


Genetic drift refers to random fluctuations in the gene frequency of a population.






facts


1.The Hardy-Weinberg law states that under certain conditions ,the gene frequency of a population does not change from generation to generation.


2.The founder effect occurs when the gene frequency of a newly established population is somewhat different from the parental population. This may be due to the small sample of founding individuals


3. Migration can change the gene frequency of a population if the migrants have a different gene frequency than that of the population they are leaving or entering.


4.Gene frequency refers to the proportion of alleles that are of a particular type


5.The Hardy-Weinberg principle states that if the following conditions are met, the gene frequency of a population will not change from generation to generation:

diagram

this small widlflower population has a stable size of ten plants. suppose that by chance only five plants of generation 1 produce ferile offspring. this could occur, for example, if only those plants happend to grow in a location that provided enough nutrients to support the production of offspring. again by chance, only two plants of generation 2 leave ferile offspring. as a result, by chance alone, the frequency of the a allel first increases in generation 2, then falls to zero in generation 3.

video

http://www.youtube.com/watch?v=4Kbruik_LOo&feature=fvst

summary

Evolution, the science of how populations of living organisms change over time in response to their environment, is the central unifying theme in biology today.
One of the most important tools population genetics gave to the study of evolution was the principle of Hardy-Weinberg equilibrium. This principle states that there is nothing in gene replication, meiosis, fertilization, or reproduction that changes the frequency of gene alleles over time.Since these are the assumptions that must hold true for the Hardy-Weinberg equilibrium to be maintained, their opposites are the causes of evolution, or the change of allele frequencies in populations. For example, mutation can cause changes in allele frequency by creating new, altered genetic material while gene flow can change allele frequencies by introducing new alleles to the population through immigration or removing alleles through emigration. Of these five causes of evolution, only the last one involves natural selection, or directional change imposed by survival of the fittest in a harsh environment. The first four, all of which can play critical roles in evolution, involve chance events.