Speciation       1. Describe the role of isolating Mechanisms in Speciation        2. Decide whether selection is occurring in a population by determining gene frequencies using the Hardy-Weinberg Equilibrium theory

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• The development of a new species is called speciation. 
• Some of the ways new species may occur are by by polyploidy, a genetic bottleneck, mating preference, punctuated equilibrium, or gradualism. 
• There are 3 models for how speciation occurs.

1) allopatric speciation: new species form gradually from with a population that becomes geographically isolated; populations don't mix; then genetic divergence occurs
2) sympatric speciation: new species arise from within an exisiting population; speciation within a panmictic population
3) parapatric speciation: species at the border between 2 populations interbreed to form new species; often induced by environmental changes
A fourth is sometimes added: Allo-Parapatric Speciation -- populations initially separat (allo-) but then secondarily come into contact with subsequent parapatric speciation

Hardy-Weinberg Equilibrium Theory

The Hardy Weinberg Equilibrium Theory predicts how gene frequencies will be transmitted from generation to generation given a specific set of assumptions.
    A.Assumptions 
        1.large population - to insure no sampling error from one generation to the next 
        2.random mating - no assortive mating or mating by genotype 
        3.no mutations - or mutational equilbrium, so that the alleles don't change; even new mutations have little effect on allele frequencies from one generation to the next 
        4.no migration between populations 
        5.no natural selection - all genotypes reproduce with equal success 
     B.Basic Relations 
        1.two alleles at a gene - A and a 
        2.frequency of the A allele = p 
        3.frequency of the a allele = q 
        4.p + q = 1 
        5.1 - q = p 
     C.Hardy Weinberg Equation 
         Genotype frequencies are given by the equation: p² + 2pq + q²  = 1
        The frequency for getting AA is equal to p².
        The frequency for getting Aa is equal to 2pq.
        The frequency for getting aa is equal to q².
         For example, in a given gene pool you have 40 alleles ... 16 A and 24 a.
            p = 16/40 = .4 --- this gives you the percentage of A's ... .4 x 100% -> 40%
           q = 24/40 = .6--- this gives you the percentage of a's ... .6 x 100% -> 60%
        Using the H-W Equation, we can find the probabilities of the different allele combinations.
            p²  = .4 x .4 = .16
            2pq = 2 x .4 x .6 = .48
            q²  = .6 x .6 = .36
            So the probability of getting AA is 16%, the probability of getting Aa is 48%, and the probability of getting aa is 36%.

Hardy-Weinberg states that evolution will not occur in a population if seven conditions are met:
    1.  mutation is not occurring
    2.  natural selection is not occurring
    3.  the population is infinitely large
    4.  all members of the population breed
    5.  all mating is totally random
    6.  everyone produces the same number of offspring
    7.  there is no migration in or out of the population
Since it is unlikeley that these 7 conditions would be met, evolution does occur.

You can use the H-W results to determine whether selection is occurring in a population.  By comparing genotype frequencies from the next generation with those of the current generation in a population, one can  learn whether or not evolution has occurred and in what direction and rate for the selected trait.