Lecture 7 BIO 311D 1st Edition Outline of Last Lecture I The Smallest Unit of Evolution II The Hardy Weinberg Equation III Genetic Variation IV Variation Within and Between Populations V Sources of Genetic Variation VI Altering Gene Number or Position Outline of Current Lecture I Hardy Weinberg Equilibrium II Conditions for the Hardy Weinberg Equilibrium III Apply the Hardy Weinberg Principle IV Natural selection genetic drift and gene flow can alter allele frequencies in a population V Genetic Drift The founder effect and the bottleneck effect VI The Key Role of Natural Selection in Adaptive Evolution VII Sexual Selection Current Lecture Hardy Weinberg Equilibrium 1 Which of these populations are in hardy Weinberg equilibrium The original population has 36 red 48 roan and 16 white Population A 36 red 48 roan 16 white Population B 40 red 40 roan 20 white Answer Population A because the Hardy Weinberg equilibrium is when a population that has not yet evolved Chapter 22 will not be on the exam Conditions for Hardy Weinberg Equilibrium 1 No mutations 2 Random mating 3 No natural selection 4 Extremely large population size 5 No gene flow We as humans do not fit into the hardy Weinberg equilibrium because we whether consciously or unconsciously naturally select our partners Applying the Hardy Weinberg Principle We can assume the locus that causes phenylketonuria PKU is in Hardy Weinberg equilibrium given that The PKU gene mutation rate is low Mate selection is random with respect to whether or not an individual is a carrier for the PKU allele Natural selection can only act on rare homozygous individuals who do not follow dietary restrictions The population is large Migration has no effect as many other populations have similar allele frequencies The occurrence of PKU is 1 per 10 000 births q2 0 0001 found by 1 10 000 q 0 01 found by taking the square root of 0 0001 The frequency of normal alleles is p 1 q 1 0 01 0 99 The frequency of carriers is 2pq 2 0 99 0 01 0 0198 or approximately 2 of the U S population Natural selection genetic drift and gene flow can alter allele frequencies in a population Three major factors alter allele frequencies and bring about most evolutionary change Natural selection Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions Example an allele that confers resistance to DDT increased in frequency after DDT was used widely in agriculture The only mechanism that consistently causes adaptive evolution New genetic variations includes both chance and sorting Genetic drift When certain allele frequencies are reduced from one generation to the next due to chance occurrences or something that happens within a population to cause that The smaller a sample the greater the chance of deviation from a predicted result Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next Genetic drift tends to reduce genetic variation through losses of alleles Gene flow Consists of the movement of alleles among populations Important agent of evolutionary change in human populations Alleles can be transferred through the movement of fertile individuals or gametes Gene flow tends to reduce variation among populations over time Can decrease the fitness of a population Example the great tit Parus major on the Dutch island of Vlieland Mating causes gene flow between the central and eastern populations Immigration from the mainland introduces alleles that decrease fitness Natural selection selects for alleles that increase fitness Birds in the central region with high immigration have a lower fitness birds in the east with low immigration have a higher fitness Can also increase the fitness of a population Example the spread of alleles for resistance to insecticides Insecticides have been used to target mosquitoes that carry West Nile virus and malaria Alleles have evolved in some populations that confer insecticide resistance to these mosquitoes The flow of insecticide resistance alleles into a population can cause an increase in fitness A high proportion of the cats on Key West have extra toes polydactyl what is most likely explanation A High rate of mutation B Founder effect C Bottleneck effect D Directional Selection for extra toes Answer The founder effect Genetic Drift The founder effect and the bottleneck effect The Founder Effect Occurs when a few individuals become isolated from a large population Common in small populations Allele frequencies in the small founder population can be different from those in larger parent population Because a certain population of those founders had this syndrome they passed it on to their offspring Their population has a higher percentage of individuals with the disease The Bottleneck Effect This is a sudden reduction in population size due to a change in the environment The resulting gene pool may no longer be reflective of the original populations gene pool If the population remains small it may be further affected by genetic drift The bottleneck effect can increase understanding of how human activity affects other species Example Elephant population decreased at a fast rate due to the human demand in their tusks so eventually we had to stop in order to allow the elephant population to stabilize again Relative Fitness The contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals Selection favors certain genotypes by acting on the phenotypes of certain organisms Before industrial revolution mice were skewed towards light colored furs due to the clean air and better blending into the environment for survival After the revolution due to coal mice had darker colored fur due to blending in the environment Three modes of selection o Directional selection favors individuals at one end of the phenotypic range o Disruptive selection favors individuals at both extremes of the phenotypic range o Stabilizing selection favors intermediate variants and against extreme phenotypes The Key Role of Natural Selection in Adaptive Evolution Striking adaptations have arisen by natural selection For example cuttlefish can change color rapidly for camouflage For example the jaws of snakes allow them to swallow prey larger than their heads Natural selection increases the frequencies of alleles that enhance survival and reproduction Adaptive evolution occurs as the match between an organism and