Bellringer Please get out your lab and Notes. complete the questions on the lab. NO COPYING. Population Genetics The study of genetic traits and changes in populations. Population Genetics 1. Gene pool The combined genetic information of all the members of a particular population. Population Genetics 2. Allele frequency Is the number of times that an allele occurs in a gene pool compared with the number of times other alleles occur (ex. beans and bunnies lab). Population Genetics 3. Genetic equilibrium Allele frequencies remain constant. ►Is this even possible in a changing environment?...... Population Genetics 5 Conditions to maintain genetic equilibrium 1. Random mating 2. Population must be very large 3. No immigration/emigration 4. No mutations 5. No natural selection! Therefore, if the gene frequency of a population changes then it must have “evolved”! Mechanisms of Evolution Mechanisms of Evolution There are several: 1. Natural Selection 2. Gene Flow 3. Genetic drift 4. Mutations 5. Non-random mating 1. Natural Selection .Nature decides .Populations, not individuals, evolve 1. Natural Selection: . Affects variation in a population as the better adapted (more fit) individuals survive and reproduce, passing on their genes to the successive generations. Acts only upon an organisms phenotype. If the phenotype is better suited for a changing environment, the individual can survive and pass on its genes. Natural Selection 6. Gene Flow Transport of genes by migrating individuals . New genes in a population by means other than mutations. EX: migration of birds. Gene Flow 5. Genetic Drift Change in the gene pool that takes place strictly by chance. .Affects small populations .Increases the chance of rare alleles EX: shipwreck survivors colonizing an island Examples of Genetic Drift . A) The Founder Effect: . Small population that branches off from a larger one may or may not be genetically representative of the larger population from which it was derived. Only a fraction of the total genetic diversity of the original gene pool is represented in these few individuals. Examples of Genetic Drift . B) Population Bottleneck: . Occurs when a population undergoes an event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing. •The event may eliminate alleles entirely or also cause other alleles to be over- represented in a gene pool. EX. Cheetahs 4. Mutations . Causes genetic change . Can occur by chance . Many are lethal . Quickly eliminated . Some are useful . Become part of gene pool by the process of natural selection 5. Non-Random Mating . In animals, non-random mating can change allele frequencies as the choice of mates is often an important part of behaviour. Many plants self-pollinate, which is also a form of non- random mating (inbreeding). Charles Darwin’s finches.