32 population genetics and evolution worksheet PDF

Preview

Summary

population genetics worksheet from class you can use to help you on the subject. I hope this is helpful....

Description

#32- Population Genetics and Evolution Population Genetics  Population- group of organisms, members of same species in same geo area o Evolution @ population level o (natural selection @ individual) Individual Population



Life span One generation Many Genetic characterization Genotype Allele frequencies Genetic variability None Considerable Evolution None Can change over time Population geneticists focus on two areas: o 1. Measurement of genetic variation w/in population  Morphological characters- variations in length, weight, coloration  Molecular characters- variations in nucleotide sequences of DNA or amino acid sequences of proteins o 2. Mechanisms by which genetic variation changes over space and time

Genetic Variation  Variation measured w/in and b/w populations  Monomorphic- no variation/only one form exists (all grey fur squirrels)  Polymorphic- variation (gray or black fur) Genetic Composition of a Population  Genotype fixed @ moment gametes unite forming diploid zygote  genetic makeup- frequency of alleles that exist in population o ex: CF in 4% of population.  wild-type allele frequency = .96 (96%) Probability and Populations  Hardy-Weinberg equation- allele frequencies o PKU disease = q o Normal/wild-type = p  Homozygous for PKU = q * q = q2  Homozygous wild = p * p = p2  Heterozygous in a population = p*q=pq 2 o P + 2pq + q2 = 1 o P+q=1

Multiple Alleles Lol

Evolution and Population Size  Small populations = vulnerable to loss of genetic variability  The larger the pop. The more buffer against random variations Genetic Drif  Genetic drif- random fluctuations of allele and genotype frequencies o Small populations more Bottleneck Effect  Bottleneck effect- natural disaster/overhunting decimates population, only few survive, and they don’t show genotype/allele frequencies of original population Founder Effect  Founder effect- few individuals (founders) get geographically separated, form new population, don’t show original features o Colonized remote islands  Inbreeding Gene Flow  Gene flow – bringing/taking new alleles via migration Mutations  Mutation- change in DNA o Ultimate source of all genetic variation o Low raterarely a strong evolutionary force Random vs. Nonrandom Mating  Random  genetic stability  Non-random  less diverse o Neighbors  Assortative mating- individuals choose mates w/ same phenotypic traits as themselves

Genetic Stability and Selection Pressure  To maintain Hardy-Weinberg equilibrium, all individuals must have: o same reproductive capacity and fitness o large population size o no gene flow o random mating o no net mutations

Summary: This tutorial covered the basic principles of population genetics. A population is a group of organisms that are members of the same biological species and that live in the same geographic area. Characters in a population can be monomorphic, showing no variation, or polymorphic, having at least two different variants. Variation can be caused by the organism's genotype or by environmental effects. The Hardy-Weinberg equation can be used to

examine genetic variation within populations. In the case of two alleles for a gene, the sum of the frequency of the alleles equals 1 or 100%. This is represented by the equation p + q = 1. To determine the frequencies of the three possible genotypes, use the equation p2 + 2pq + q2 = 1. When the allele frequencies stay the same between generations, the population is in Hardy-Weinberg equilibrium. Hardy-Weinberg equilibrium requires that allele frequencies within a population remain the same from one generation to the next, as long as certain conditions (including no mutation, large population size, no migration, random mating, and no natural selection) are met. The next tutorial will explore the evolutionary forces that can cause changes in allele and/or genotype frequencies in a population; that is, changes that lead to evolution. The Hardy-Weinberg equation can be used to determine the allele frequency in a population. Thus, it provides a useful tool to describe the degree of evolution that is taking place over successive generations. Not all populations are undergoing evolution at all times. In certain stable environments, many populations show no evidence for evolution. (Although if the conditions change, then evolution can take place.) There are a number of conditions that predictably decrease evolution; namely: large populations that are more genetically stable compared to smaller populations; no migration/immigration by which new alleles are introduced or removed from a population; no mutations to introduce new alleles; random mating that allows all individuals equal access to all alleles and; no natural selection, which causes changes in allele frequencies due to fitness differences between individuals. Conversely, opposing conditions increase evolution; namely: small populations are genetically unstable because they are susceptible to genetic drif; migration/immigration that allows alleles to enter or leave a population; mutations that introduce new alleles; nonrandom matings that cause unequal access to all alleles; and natural selection that changes allele frequencies based upon individuals' reproductive capacity and fitness....