Genetic Variation 1 PACKET 60 CHAPTER 23 1232022

Genetic Variation 1 PACKET #60 CHAPTER #23 1/23/2022 8: 48 AM

Introduction 2 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 1/23/2022 8: 48 AM

Examination of Genetic Variation 3 1/23/2022 8: 48 AM

Examination I 4 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 1/23/2022 8: 48 AM

Balanced Polymorphsim 5 1/23/2022 8: 49 AM

Balanced Polymorphism Maintenance in a population 6 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. 1/23/2022 8: 49 AM

Hetereozygote Advantage 7 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. 1/23/2022 8: 49 AM

Frequency Dependent Selection 8 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. 1/23/2022 8: 49 AM

Frequency Dependent Selection 9 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. 1/23/2022 8: 49 AM

Neutral Variation 10 1/23/2022 8: 49 AM

Neutral Variation 11 Observed in a population where variation does not alter the ability of an individual to survive and reproduce. 1/23/2022 8: 49 AM

Geographic Variation 12 TYPE OF GENETIC VARIATION 1/23/2022 8: 49 AM

Geographic Variation 13 � 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? 1/23/2022 8: 49 AM

Review 14 Balanced Polymorphism Genetic Variation Neutral Variation Heterozygote Advantage Frequency Dependent Selection Geographic variation 1/23/2022 8: 49 AM