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Genetic Variability and Equilibrium What you have already learned… 1. Genetic variation exists within inherited traits in every population. 2. Variation exists in the phenotypes of individuals within populations. 3. Genetic variation can either help or harm individuals. 4. It is better to have variation within a population. – Environmental change occurs and wipes out half of population that did not have the traits to survive; other phenotypes that existed in the population did survive and can continue to breed successively. Genetic Variation • Populations with lots of genetic variation normally also have a lot of variation in phenotype • Variation is good in a population because it allows the species to adapt to a changing environment Gene Pool • The genetic variation of a population is stored in a populations gene pool • The gene pool is the set of all the different alleles within a population • Different combinations of alleles occur when individuals in the population mate Factors that Influence Genetic Variability 1. Gene Flow: the movement of genes from one population to another as individuals move between populations – Increases the genetic variation of the receiving population Gene Flow (cont.) • The less gene flow there is between populations the more genetically different the two populations become as they each adapt to their different environments – Eventually the two populations may become so different that they form different species Factors that Influence Genetic Variability 2. Genetic drift: changes in allele numbers due to chance – – Causes a loss in genetic diversity Change of alleles is more noticeable in smaller populations. Bottleneck Effect • Occurs when some kind of event greatly reduces the size of a population Founder Effect • Occurs when a small number of individuals colonize a new area Factors that Influence Genetic Variability 3. Sexual Selection (nonrandom mating): occurs when certain traits increase mating success – – – Males compete for females Males display traits that attract females The alleles for these traits become more common because the individuals with the traits mate more successfully Factors that Influence Genetic Variability 4. Mutations: increase the genetic variation by introducing new alleles 5. Natural Selection: allows for the most favorable phenotypes to survive and be passed on to future generations. Hardy Weinberg Equilibrium • The frequency of alleles can remain constant if certain conditions are met. • When a population’s allele frequency remain the same that population is said to be in Hardy-Weinberg Equilibrium (genetic equilibrium) Genetic Equilibrium (HardyWeinberg Principle) • Five conditions that are required to maintain genetic equilibrium: 1. The population must be very large, no genetic drift occurs. 2. No migration into or out of a population 3. There must be random mating 4. There must be no mutations within the gene pool. 5. There must be no natural selection.