PROCESS OF EVOLUTION I (Genetic Context). Since the Time of Darwin Darwin did not explain how variation originates or passed on The genetic principles.
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Presentation on theme: "PROCESS OF EVOLUTION I (Genetic Context). Since the Time of Darwin Darwin did not explain how variation originates or passed on The genetic principles."— Presentation transcript:
Since the Time of Darwin Darwin did not explain how variation originates or passed on The genetic principles were recently applied to populations to explain how evolution occurs Evolution: changes in the genotype & phenotype of populations overtime
Microevolution Gene pool: all alleles found in a population Microevolution: a change in the gene pool of a population from generation to generation Allelic frequency: number of alleles (in question) divided by the total number of alleles in the gene pool Genotypic frequency: the number of a specific genotype divided by the total number of genotypes in the population A change in allelic & genotypic frequencies are used to measure evolution
Hardy-Weinberg Equilibrium They recognized that allelic frequencies in a gene pool will remain constant over time if certain conditions were met: 1.No mutation 2.No gene flow (No migration) 3.Random mating 4.No genetic drift (population is large) 5.No selection (all genotypes are equally important) If these conditions are met there will be no evolution The last two are the main causes of evolution
Calculating genotypic & Phenotypic Frequencies The population under study is sampled Using electrophoresis: alleles, homozygous dominant & recessive, and heterozygous were determined Using the equations below, conclusion were made on evolution Calculating Frequencies Using Hardy-Weinberg Equations Allelic frequency: p + q = 1 Genotype frequency: p 2 + 2pq + q 2 = 1
Causes of Microevolution Deviations from Hardy-Weinberg conditions can result in genetic changes that lead to evolution
Gene Flow Gene flow: movement of alleles between interbreeding adjacent populations Introduce new genes in a population Continuous gene flow makes the gene pool of populations similar preventing evolution
Nonrandom Mating Deviations from random mating: Inbreeding: It increases both homozygous dominant & recessive Assortative mating: favors similar phenotypes It divides the population into two or more phenotypes Sexual selection: e.g., female chose their mates
Genetic Drift Genetic drift: a random process that results in changes of allele frequencies It occurs more frequently in small populations Bottleneck effect: genetic drift that occurs when only few individuals of a population remains Populations carry only a fraction of the original genes Each individual in the population become important. why?
Founder Effect (an example of genetic drift) A founder is one or few individuals separated by geographical barriers from the main population The founder population carries only a small fraction of the genetic diversity in the original population Genetic drift in the new colony is called a founder effect It is a condition where rare alleles occur at higher frequencies