Genetic Variation PACKET #60 CHAPTER #23 2/23/2019 10:10 PM

Introduction Genetic variation is necessary for natural selection There are multiple reasons for genetic variability in populations Mutations Crossing over Independent assortment Random fertilization of eggs by sperm 2/23/2019 10:10 PM

Examination of Genetic Variation 2/23/2019 10:10 PM

Examination I One way of evaluating genetic variation is to examine genetic polymorphism. The presence of two or more alleles for a given locus To examine genetic polymorphism, biologists compare different forms of a particular protein. Each form consists of a slightly different amino acid sequence that is coded for by a different allele. Gel electrophoresis 2/23/2019 10:10 PM

Balanced Polymorphsim 2/23/2019 10:10 PM

Balanced Polymorphism Maintenance in a population of two or more alleles in equilibrium at frequencies too high to be explained, particularly for the rarer of them, by mutation Balanced polymorphism, a special type of genetic polymorphism, may be a result of natural selection. The mechanisms that allow balanced polymorphism to exist while allow natural selection to occur is: - Hetereozygote Advantage Frequency Dependent Selection. 2/23/2019 10:10 PM

Hetereozygote Advantage Hetereozygote exhibits greater “fitness” than either homozygotes. Example Hetereozygote carriers of the sickle cell allele. Provides individuals resistance to malaria. Allows individuals living in areas where malaria is high to survive. Those that are homozygous recessive are likely to die at an early age. Those are homozygous dominant, having regular red blood cells, are likely to die if infected with malaria. What type of mutation caused the sickle shaped cell to occur (i.e. the recessive allele)? 2/23/2019 10:10 PM

Frequency Dependent Selection The “fitness” of a particular phenotype depends on how often it appears within a population. The ability of a phenotype to be “fit” depends on the how often it appears within a population. Often a phenotype has a greater selective value when rare then when common in a population. If a phenotype falls within this category, they lose their selective advantage as they become more common. 2/23/2019 10:10 PM

Frequency Dependent Selection Example Scale-eating cichids Two forms Right pointing mouths & left pointing mouths Right pointing allele is dominant Get food by biting off the scales of other fish Those with right pointed mouths attack prey’s left flanks If the prey is constantly being attacked from a particular side, then they become more wary to such attacks When the prey become wary, the advantage then swings to those predators that attack from the opposite side The reason for the frequency of both forms of cichids have osculating over the last 20 – 30 years. 2/23/2019 10:10 PM

Neutral Variation 2/23/2019 10:10 PM

Neutral Variation Observed in a population where variation does not alter the ability of an individual to survive and reproduce. 2/23/2019 10:10 PM

TYPE OF GENETIC VARIATION Geographic Variation TYPE OF GENETIC VARIATION 2/23/2019 10:10 PM

Geographic Variation Genetic variation among individuals of different populations of the same species. Cline Type of geographic variation Gradual change in a species’ phenotype and genotype frequencies through a series of geographically separate populations due to an environmental gradient. Example Common Yarrow (Achilea millefolium) Wild-flower that grows in various North American habitats. Exhibits clinal variation in height Due to different climates at different elevations/altitudes. Could clinal variation result in a new species? 2/23/2019 10:10 PM

Review Genetic Variation Balanced Polymorphism Heterozygote Advantage Frequency Dependent Selection Neutral Variation Geographic variation 2/23/2019 10:10 PM