PROCESS OF EVOLUTION I (Genetic Context)

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