Chapter 16 Evolution of Populations

Ch. 16 Evolution of Populations 16–1Genes and Variation A.How Common is Genetic Variation? –Most genes have two forms. –Many genes have multiple alleles. –Many traits are polygenic. B.Variation and Gene Pools Gene pools have frequency of certain traits. This frequency changes over time. –This increases or decreases the variation in the population

Ch. 16 Evolution of Populations C.Sources of Genetic Variation 1.Mutations itdna/crops04activity.jsphttp:// itdna/crops04activity.jsp 2.Gene Shuffling Independent assortment of chromosomes during meiosis. D.Single-Gene and Polygenic Traits –2 phenotypes vs. many phenotypes2 phenotypes many phenotypes Click here to go to next outline 

Ch. 16 Evolution of Populations Frequency Of phenotype Phenotype (height) Polygenic Traits will make a bell curve when graphed Click here to return to outline- 

Ch. 16 Evolution of Populations A single gene trait makes a bar graph with two phenotypes Click here to return to outline

Ch. 16 Evolution of Populations 16–2 Evolution as Genetic Change A.Natural Selection on Single-Gene Traits –Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution. Run this simulation of the perrered moth evolution. eets/pepperedmoth.html

Ch. 16 Evolution of Populations B.Natural Selection on Polygenic Traits Natural selection can affect the distributions of phenotypes in any of three ways 1.Directional SelectionDirectional Selection 2.Stabilizing SelectionStabilizing Selection 3.Disruptive SelectionDisruptive Selection

Ch. 16 Evolution of Populations –C.Genetic Drift Sample of Original Population Founding Population A Founding Population B Descendants Click here to continue with outline

Ch. 16 Evolution of Populations Click to return to outline Low mortality, high fitness High mortality, low fitness Directional Selection

Ch. 16 Evolution of Populations Click here to return to outline

Ch. 16 Evolution of Populations Click here to continue with outline

Ch. 16 Evolution of Populations D.Evolution Versus Genetic Equilibrium The Hardy-Weinberg principle states that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change. In other words, as long as everything stays the same, evolution will not happen.

Ch. 16 Evolution of Populations Genetic Equilibrium Five conditions are required to maintain genetic equilibrium from generation to generation 1. Random Mating 2. Large Population 3. No Movement Into or Out of the Population 4. No Mutations 5. No Natural Selection

Ch. 16 Evolution of Populations 16–3The Process of Speciation-how do species evolve? A.Isolating Mechanisms-ALL types of isolation result in Reproductive Isolation. 1.Behavioral Isolation-have differences in courtship rituals 2.Geographic Isolation-are separated by geographic barriers such as rivers, mountains, or bodies of water. 3.Temporal Isolation-reproduce at different times.

Ch. 16 Evolution of Populations B.Testing Natural Selection in Nature Examples of Evolution observed in Nature Peppered Moth Antibiotic resistance in bacteria Human adults who can digest milk Gypsy Moth Insects able to survive insecticides Plants able to survive herbicides Darwin’s finches-see next page Sickle cell trait in humans

Ch. 16 Evolution of Populations C.Speciation in Darwin’s Finches 1. Founders Arrive-birds arrive from S. America perhaps blown there by a storm 2. Separation of Populations-The small population is separated on different islands. 3. Changes in the Gene Pool-Natural variation due to mutation occurs 4. Reproductive Isolation-Birds are isolated by behavior and geography 5. Ecological Competition-Each island has specific foods in limited amounts 6.Continued Evolution-all of these drive changes in the population (evolution) which is documented even today

Ch. 16 Evolution of Populations D. Studying Evolution Since Darwin Advances in genetics, molecular biology, ecology, physics and chemistry increase the evidence that species change over time and continue to change. E. Limitations on Research Evidence of change exists. But no one has yet witnessed the formation of a brand new species. Many new discoveries have led to new hypotheses that refine and expand Darwin's original ideas. Even Darwin has evolved. There are still many unanswered questions.