Allele Frequencies in Populations: Hardy-Weinberg Law Assumptions Already Made (Cant Control) 1) Population Size 2) Mutation 3) Natural Selection 4) Immigration/emmigration 5) Non-random mate choice Can Control 2) Natural Selection Control Variable Left side Experimental Variable Right Side Comparisons are most meaningful when there is only ONE difference between populations For this experiment only the population size should be different and everything else should be the same. Always make sure the Initial Genotype
Frequencies and Natural Selection Genotype Viability are the same values for all Genotypes. To determine the “a” allele To determine the “A” allele The population that is closest to being In the Hardy-Weinberg equilibrium experiment is the control because the population is larger. Effect of Natural Selection Genotype and Allele Frequencies We want to compare the results when the Natural Selection Genotype Viabilities are different. “AA” and “Aa” mosquitoes are resistant to DDT. This is a high Natural Selection Genotype Viability.
The “aa” mosquitoes have a low viability; meaning they are selected against by the DDT environmental factor. The result is AA is exponentially growing Aa and aa are exponentially decaying 1) This is because A is the dominant Allele and “a” is affected so it will decrease and with less aa and Aa then there is less competition so AA will increase The frequency of the “a” allele will decay to almost zero for Aa, but it will never die because Aa will survive because of the “A” allele but the aa genotype will die. NOTES Each gene carries particular alleles.
We simplify by ignoring all but a single pair of alleles from each organism. Genotype Frequency- the fraction of a population with a particular genotype Allele Frequency- The fraction of a particular allele in the population’s gene pool Hardy-Weinberg Law- states tnat In tne aosence 0T evolutlonary Torces, tne allele ana genotype Trequencles of a sufficiently large population do not change. Follow generation after generation and has the same allele and genotype frequency Evolution- The change in allele or enotype frequencies of a population over time.
Population- A localized group of interbreeding species members Gene Pool- The entire collection of alleles in a population Genotype- The genetic composition of an individual Allele- one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. = Frequency of DD genotype = Frequency of dd genotype Frequency of Dd genotype In the real populations none of the five assumptions can be completely isolated.