* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Mechanisms for Evolution
Genetics and archaeogenetics of South Asia wikipedia , lookup
Deoxyribozyme wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
Designer baby wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Behavioural genetics wikipedia , lookup
Public health genomics wikipedia , lookup
Genetic engineering wikipedia , lookup
History of genetic engineering wikipedia , lookup
Genetic testing wikipedia , lookup
Heritability of IQ wikipedia , lookup
Genome (book) wikipedia , lookup
Dual inheritance theory wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Human genetic variation wikipedia , lookup
Group selection wikipedia , lookup
Sexual selection wikipedia , lookup
Koinophilia wikipedia , lookup
Genetic drift wikipedia , lookup
Mechanisms for Evolution Populations and Evolution Population – a group of organisms that interbreed Each population shares a gene pool The gene pool contains the different alleles present in the population Populations and Evolution The allele frequency is the number of times each allele occurs in the gene pool. The frequency of alleles in a population tends not to change unless there is an outside force causing it Allele frequencies change because of Mutations Mutations can affect allele frequency in a population by 1. Adding new alleles for a trait 2. Changing the amount of each allele present It can take a long time to eliminate a mutation and a long time for a new mutation to become prevalent Evolution occurs because of changes to the equilibrium 1. 2. 3. 4. There are 4 mechanisms that can change the allele frequencies in a population Natural Selection Migration Genetic Drift Non-random Mating 1. Natural Selection 1. Natural Selection Natural selection: the process by which individuals who are more fit for the environment survive and reproduce There are 4 different types of natural selection: a. Stabilizing Selection b. Directional Selection c. Disruptive Selection d. Sexual Selection 1a. Stabilizing Selection Stabilizing selection occurs when individuals with the average form of the trait are most fit for the environment and extreme traits are eliminated This is the most common form of selection and works in all populations at all times Example of stabilizing selection Lizard body size: Large lizards are easily seen by predators, but smaller lizards cannot run as fast to escape the predators Mid sized lizards are most fit in the environment, so they survive and reproduce more often, changing the allele frequencies in the population 1b. Directional Selection Directional selection occurs when individuals with one extreme of variations are the most fit in the environment. This causes a gradual shift in allele frequency to that extreme. Example of Directional Selection Anteater tongue length: Anteaters with long tongues are most fit because of the depth of the nests of the termites they eat. 1c. Disruptive Selection Disruptive selection occurs when both extremes of variations are the most fit Therefore, there is selection against the middle variations (in other words, those with neither extreme tend to die out) 1c. Disruptive Selection Ex: Limpet shells Dark limpets blend with bare rocks Light limpets blend with barnacle covered rocks Tan limpets are visible in both situations and get preyed upon by birds 1d. Sexual Selection Sexual selection is natural selection arising through preference by one sex for certain characteristics in individuals of the other sex. Mates tend to be chosen for their phenotypes and females tend to choose the males 1d. Sexual Selection Sexual selection not only includes mate choice but also encompasses male-male competition and female-female competition. Ex: larger females out-compete smaller females Sexual Selection cont’d Ex: Peacocks Male peacocks have large tail feathers that make it difficult to fly and escape from predators Female peacocks choose males based on their tail feather length and fullness Over time males with larger tail feathers reproduce more causing large tails to be selected for Sexual Selection in Peacocks (3 min.) 2. Migration Movement into and out of a population can change the allele frequency in a population’s gene pool Immigration can ADD individuals with variations to the population Emigration can REMOVE individuals with variations from a population 2. Migration 3. Genetic Drift Genetic drift is the change in the gene pool of a small population that takes place strictly by chance. In smaller populations the allele frequency can change more rapidly than in larger populations 3. Genetic Drift cont’d The founder effect is a special case of genetic drift The founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population 3. Genetic Drift cont’d: Founder Effect 4. Non-Random Mating Non random mating: any mating system in which males are not randomly assigned to females This occurs in populations in which individuals select mates based on observable traits 4. Non-Random Mating The result of non random mating is that some individuals have more opportunity to mate than others Thus, those deemed “more fit” produce more offspring, and their traits are more likely to be passed on Genetic Drift Simulation This simulation, like evolution itself, is based on random events. You will roll a die to choose a random number To complete the manual version of the Genetic Drift Simulation you need the Worm Worksheet and colored pencils in 5 different colors Genetic Drift Simulation Genetic Drift Simulation Genetic Drift Simulation Genetic Drift Simulation Keep rolling the die until you have 5 dots Genetic Drift Simulation Genetic Drift Simulation Genetic Drift Simulation Genetic Drift Simulation Genetic Drift Simulation 1. What is genetic drift? 2. Today you looked at 5 populations made of 5 individuals each. If your populations were made of 500 individuals instead of 5, would the allele frequencies have changed more or less rapidly than what you saw in your simulation? Why? 3. Describe the founder effect. 4. How many generations did it take each of your populations to become homogenous? (homogenous = all the same color) 5. Based on what you did in the simulation, describe the role randomness plays in genetic drift.