Transcript Slide 1
Evolution: it’s all about mutations that aid survival and reproductive selection Natural selection… is the process by which those ______________that make it more likely for an ______________ to survive and successfully ______________ become more common in a ______________ over successive generations. It is a key mechanism of ______________. Natural selection… is the process by which those heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations. It is a key mechanism of evolution. Let’s start out with the gene pool • The gene pool is the combined genetic info of all the members of a population • The gene pool can consider all of the traits of the population, or just one of the traits. Let’s try looking at our gene pool… Some traits in the gene pool are easier to study than others: • The # of phenotypes of a given trait indicate the # of genes controlling that trait – How many genes control this trait? Some traits in the gene pool are easier to study than others: • The # of phenotypes of a given trait indicate the # of genes controlling that trait – How many genes control this trait? 1, it is a single gene trait Polygenic traits are represented by a bell-shaped curve How and why does the gene pool change? The two main sources of genetic variation: 1. Mutations 2. Gene shuffling, that results from sexual reproduction during meiosis Natural Selection on polygenic traits can happen in 3 basic patterns. Which areas on the map have the highest fitness? The highest mortality/selection pressure? • Which graphs of natural selection best relate to Darwin’s tortoises? Finches? Genetic drift: Random change/event affects allele frequency in a population Founder effect… can result in genetic drift, when a sub-population becomes isolated. What is an example? More genetic drift Evolution vs. genetic equilibrium 5 factors must exist to maintain genetic equilibrium from generation to generation 1. 2. 3. 4. 5. Random mating The population must be very large No movement into or out of the population No mutations No natural selection The Hardy-Weinberg principle states that allele frequency in a population will remain constant unless one or more of these factors cause change Hardy-Weinberg and genetic equilibrium explained mathematically Early in the twentieth century mathematician Godfrey Hardy and physician Wilhelm Weinberg independently developed a model describing the relationship between the frequency of the dominant and recessive alleles (hereafter, p and q ) in a population. p 2 + 2 pq + q 2 They reasoned that the combined frequencies of p and q must equal 1, since together they represent all the alleles for that trait in the population: Hardy and Weinberg represented random mating in the population as the product (p + q)(p + q), which can be expanded to p 2 + 2 pq + q 2 . This corresponds to the biological fact that, as a result of mating, some new individuals have two p alleles, some one p and one q, and some two q alleles. P 2 then represents the fraction of the population that is homozygous dominant while 2 pq and q 2 represent the heterozygous and homozygous recessive fractions, respectively. How do new species come to be? Speciation 1. Founders arrive Speciation 1. Founders arrive 2. Isolation of populations a. Geographic b. Behavioral c. Temporal Speciation 1. Founders arrive 2. Isolation of populations a. Geographic b. Behavioral c. Temporal 3. Changes in gene pool a. Shuffling b. Mutations Speciation 1. Founders arrive 2. Isolation of populations a. Geographic b. Behavioral c. Temporal 3. Changes in gene pool a. Shuffling b. Mutations 4. Become reproductively different Speciation 1. Founders arrive 2. Isolation of populations a. Geographic b. Behavioral c. Temporal 3. Changes in gene pool a. Shuffling b. Mutations 4. Become reproductively different 5. Continued evolution • Speciation video (Crash Course in Biology) • Natural selection in action (U. of Colorado)