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BIO 203L- Lecture 3

by: Karissa Sandoval

BIO 203L- Lecture 3 BIOL 203L 005

Karissa Sandoval
GPA 3.5

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Adaptation Populations Types of Natural Selection Changes in allele frequencies Hardy-Weingberg Principle
Ecology and Evolution Laboratory
Dr. Kelly Miller and Dr. Scott Collins
Class Notes
BIO 203, evolution, Adaptation, populations, Types of Natural Selection, Changes in allele frequencies, Hardy-Weingberg Principle
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This 4 page Class Notes was uploaded by Karissa Sandoval on Tuesday January 26, 2016. The Class Notes belongs to BIOL 203L 005 at University of New Mexico taught by Dr. Kelly Miller and Dr. Scott Collins in Spring 2016. Since its upload, it has received 20 views. For similar materials see Ecology and Evolution Laboratory in Biology at University of New Mexico.


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Date Created: 01/26/16
BIO 203: Evolution Lecture 3 Selection and Populations •Adaptations – Often in response to abiotic selection pressures • Ex: ability to consume oxygen better – Can involve any type of feature • Anatomical (ex: camouflage) • Behavioral (ex: ability of a rattlesnake to rattle) • Physiological (ex: venom release in a bite) – Adaptation can come from any phenotypic feature •Counter-Adaptation – Evolutionary “arms race” • Each species tries to get the upper hand and the stronger individual is the individual that wins (survival) • A player develops something that is being selected for – Examples: • Predator/prey • A snail is the prey of a crab so the snail that will survive is going to be the snail with a harder shell or visa versa the crab with a stronger pinch will survive •Non-adaptive Evolution – Not all evolution is adaptive – Example: Vestigial features (losses) • Features that are no longer used are eventually lost – Example rd • 3 codon positions in protein coding genes • 3 position changes are often “synonymous” • When you code for proteins it takes 3 proteins and some can code for the same codon •What adaptation is not – Adaptation is not acclimation – short term change in an individual • Ex: shivering when it is cold is a short term change – Adaptation is not acclimatization – long term change in an individual – Adaptation occurs over generations to populations NOT individuals •Individuals vs. populations – Organism – One individual of a species – Population – A group of organisms from the same species that regularly interact – Species – To be dealt with later – Taxon – any group of organisms (Usually named) •Units of evolution – Selection acts on organisms (individuals) – But populations evolve BIO 203: Evolution Lecture 3 – (Organisms do not evolve) •Phenotype vs. Genotype – Selection acts on the phenotype (adaptations) • Phenotype is what interacts with the environment – Results in changes in the genotype in a population (allele frequencies) • Alleles are variations in genotypes • Change in allelic frequences – Example: 10 moths, diploid, wing color depends on two alleles in a single gene (A an1 A ) 2 • A1A 1 light colored wings • A1A 2nd A A 2 2ark colored wings (Dominant) • Dark-winged moths preferentially preyed upon by birds • In white background dark moths are visible and in dark backgrounds white moths are more visible • Allelic frequencies change when predators eat the weak species • The fittest survive and reproduce = evolution • Types of Natural Selection – Directional selection • The average phenotype in a population changes in one direction • Example: Antibiotic resistance • Low resistance selected against and high resistance selected for • Shift in average value increase in frequency of high resistance to antibiotic • Directional selection reduces diversity of alleles • Purifying selection – Decline in frequency of disadvantageous alleles (same as directional) • Favorable alleles may reach frequency =1.0 (Fixation) • Unfavorable alleles may reach frequency = 0.0 (Extinction) • Doesn’t always happen • Directional selection often not constant • Opposing directional selection may be operating • Large size favored to migrate • Small size favored for speed or agility •Stabilizing selection – Selection against extremes – No change in average frequency or value of feature, but variability is reduced – Example: Birth weights BIO 203: Evolution Lecture 3 • Small size and large size babies each have higher mortality than an optimal size (combines small and large so its an in between size) • High and low birth weights selected against • Reduction in frequency of high and low birth weights, increase in frequency of optimal weight •Disruptive selection – Selection for extreme phenotypes and against average phenotypes – Opposite of stabilizing selection – Tends to increase genetic diversity – Example: Moths • Moths in areas with white surfaces and black surfaces, intermediates selected against • Light and dark moths selected for • Intermediate moths selected against • Reduction in frequency of intermediate colors, increase in frequency of extremes •Hardy-Weinberg Principle – The gene pool – all gametes available in one generation – To predict genotypes and frequency of genotypes of offspring: • Calculate random combination of randomly selected gametes – EXAMPLE • Population with 40 alleles total • Portion of alleles • p = frequency allele A = 18/40 = 0.7 (70%) • q = frequency allele A = 22/40 = 0.3 (30%) 1908, G.H. Hardy and W. Weinberg • If original allele frequencies are: A 1 p and A = 2 • In a population, then the genotype frequencies in each generation will be A A = p 2 1 1 A 1 2 2pq A 2 2 q 2 2 2 p + 2pq + q = 1 •Hardy-Weinberg Principle – Under Mendelian inheritance, allele frequencies do not change over time (in equilibrium) – If they do change, it means evolution has occurred BIO 203: Evolution Lecture 3 – In order for evolution to occur, some other factor must influence the system *Hardy-Weinberg Equilibrium is a null hypothesis for investigating evolution


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