Hardy Weinberg and Genetic equilibrium Or not

Frequency of dominant and recessive alleles remains constant from generation to generation

Meiosis and sexual reproduction are not responsible for population changes They just shuffle the genes

For genetic equilibrium to occur there are special conditions No Mutation The population is large Mating between males and females is strictly random There is no immigration or emigration No genotype is more likely to succeed than any other genotype.

Ideal Conditions When these ideal conditions are met , then there is no change in the allele frequency. These conditions are rarely met in the real world. Allele frequencies change over time. This is what is used to measure evolution.

What happens when we break the rules of equilibrium? Non-random Mating: In many species organism choose to mate with similar organisms. This causes the homozygous individuals to increase and the heterozygous individuals to decrease.

Mating rituals Many species have mating rituals to determine the strongest or “fittest”.

Harmful genes Why do they persist in populations? Whether or not a mutation is harmful or beneficial can depend on the environment. Sickle-Cell anemia is very prevalent in equatorial Africa. So is Malaria. Both kill. Let N= normal RBC Let n= sickled RBC NN Nn nn Is protected from SCA Is protected form Is killed by SCA Is killed by Malaria both Is protected from Malaria

Spontaneous mutation Dwarfism: Half of all dwarfism genes are newly mutated. Hemophilia: A sex linked trait. Your blood does not clot. So you can easily bleed to death from a bump. This gene is detrimental to health. Why doesn`t it just die out? Mutations just keep happening. 3 out of every 100,000 gametes

Large populations Statistics works well with large populations. Not necessarily in small families

Genetic drift Natural disasters kill large segments of the populations. All that genetic material is lost. A new population must begin with a much smaller gene pool. This makes a big change in the allele frequencies.

Founder effect A population in a certain area is begun with a very small number of families. A very small gene pool can encourage the growth of recessive or dangerous genes Eg Hemmingway’ s Cat Taysach’s disease in the Lac-St-Jean Huntington’s disease in western Ohio

Whooping Cranes Whooping Cranes are on the endangered species list. They nearly went extinct due to over use of DDT. They went down to 70 breeding pairs. Their population is now growing but they are still at risk because the gene pool is still small.

Migrations In the last 200 years North America has received immigrants from all over the world Each group of people has broth it’s own gene pool. This increased diversity has greatly changed the allele frequencies both in the country they left and the country they go to. High diversity is an important strategy for evolutionary success.

Equilibrium versus reality Populations don’t stay the same, they change slowly over time or evolve Change in allele frequencies is a measure of evolution Hardy Weinberg is a base line compares the ideal to the reality