BCOR 12 1st Edition Lecture 5 Outline of Last Lecture I. The Scientific ProcessII. How to Solve an Expected vs. Observed Hardy-Weinberg Problem a. Used to determine if a population is evolvingIII. Mechanisms that affect Allele FrequenciesOutline of Current Lecture I. Types of Natural SelectionII. Biological Species Concept III. SpeciationIV. Reproductive BarriersCurrent Lecture- Natural selection is the ONLY mechanism in evolution that causes shifts in the population’s traits(Figure obtained from http://www.apsnet.org/edcenter/advanced/topics/PopGenetics/Pages/NaturalSelection.aspx)To explain these curves we’ll use the example of the pocket mouse which has a variation of colors in it’s coat ranging from dark to very light. 1. Directional Selection – causes a shift in the mouse’s coat color from a medium brown, more towards a darker color. Probably due to predation on the lighter colored miceThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Disruptive Selection – mice of a medium color are preyed on more frequently than light or dark colored mice, so it causes a dip in the middle of the phenotypes3. Stabilizing Selection – mice of very light and dark colors are being preyed on so the medium color becomes the most prominent4. Is not relevant for this course.- Disruptive selection can lead to speciation- Natural selection is based on behavior, genotype, and phenotype of individuals Chapter 24 – Speciation- Biological Species Concept – a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring- Speciation – the evolutionary process in which one species splits into two or more specieso Can be slow or quick depending on what is changing- Gene flow is the ONLY mechanism that holds a gene pool of a species together. If there isn’t any gene flow between members that used to be of the same population, then speciation has occurred.There are several different species concepts but our class will be focusing on the biological species concept. But, this concept has its limitations.Limitations of the biological species concept:- Difficult to test this species concepts (ex. Hard to test with fossil evidence)- Many species reproduce asexually, this concept doesn’t apply to these individuals- It is based only on gene flowRemember that species must remain reproductively isolated from one another.Prezygotic Reproductive Barriers – barriers that restrict mating or hinder fertilization if mating does occur. Types of prezygotic reproductive barriers:- Habitat isolation- Behavioral isolation- Temporal (reproductive timing) isolation- Mechanical isolation (the sex parts don’t align between two species)- Gametic isolation (gametes don’t fuse)Postzygotic Reproductive Barriers – a reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults. Types of postzygotic reproductive barriers:- Reduced viability- Reduced hybrid fertility- Hybrid breakdownExample: A mule is a hybrid between a male donkey and a female horse, however this hybrid is sterile due to the odd number of chromosomes. This is a postzygotic barrier for the hybrid between the two species cannot breed.Example: The American Toad and the Fowler’s toad do not interbreed in the wild, but they can in captivity. What keeps them from interbreeding in the wild is the time of the year in which they breed. The American Toad breeds early in the summer while the Fowler’s toad breeds late in the summer. This is a prezygotic barrier of a temporal isolation