Chapter 19 Genetic Diversity in Populations. Chapter Outcomes: Define a gene pool. Describe the gene pool of a population at genetic equilibrium. Summarize.

Chapter 19Chapter 19

Genetic Diversity in PopulationsGenetic Diversity in Populations

Chapter Outcomes:Chapter Outcomes:

Define a gene pool.Define a gene pool.

Describe the gene pool of a population at Describe the gene pool of a population at genetic equilibrium.genetic equilibrium.

Summarize the five conditions upon which Summarize the five conditions upon which the Hardy-Weinberg principle is based.the Hardy-Weinberg principle is based.

Describe how the Hardy-Weinberg Describe how the Hardy-Weinberg equation is used to determine whether a equation is used to determine whether a population is undergoing microevolution.population is undergoing microevolution.

Chapter OutcomesChapter Outcomes

Calculate allele and genotype frequencies Calculate allele and genotype frequencies in a population.in a population.Outline the conditions required to maintain Outline the conditions required to maintain genetic equilibrium.genetic equilibrium.Identify and compare the effects of Identify and compare the effects of mutations, gene flow, non-random mating mutations, gene flow, non-random mating and genetic drift on gene pool diversity.and genetic drift on gene pool diversity.Apply the Hardy-Weinberg principle to Apply the Hardy-Weinberg principle to published data.published data.

Chapter OutcomesChapter Outcomes

Distinguish between founder effect and the Distinguish between founder effect and the bottleneck effect on gene pools.bottleneck effect on gene pools.Explain how the process of natural selection is Explain how the process of natural selection is related to microevolution.related to microevolution.Explain the cause of heterozygote advantage Explain the cause of heterozygote advantage and how it affects a gene pool.and how it affects a gene pool.Describe strategies used in captive breeding and Describe strategies used in captive breeding and population management.population management.Explain that genetic engineering can have Explain that genetic engineering can have intended and unintended effects on gene pools.intended and unintended effects on gene pools.

Genetic Diversity in PopulationsGenetic Diversity in Populations

Recall that a population is a group of Recall that a population is a group of organisms of the same species living in organisms of the same species living in one areaone area

Within a population, there are many genesWithin a population, there are many genes

The sum of the genes (and their different The sum of the genes (and their different alleles) is known as the gene poolalleles) is known as the gene pool

Gene pools are studied by population Gene pools are studied by population geneticistsgeneticists

Genotype, Phenotype & Allele Genotype, Phenotype & Allele FrequencyFrequency

Genotype Frequency:Genotype Frequency:

Phenotype Frequency:Phenotype Frequency:

Allele Frequency:Allele Frequency:

The Hardy-Weinberg PrincipleThe Hardy-Weinberg Principle

the the Hardy-Weinberg principleHardy-Weinberg principle predicts predicts that if other factors remain constant, the that if other factors remain constant, the gene pool will maintain a constant gene pool will maintain a constant composition over many generationscomposition over many generations

this is expressed by a mathematical this is expressed by a mathematical equation:equation:

The Hardy-Weinberg EquationThe Hardy-Weinberg Equation

pp22 + 2pq + q + 2pq + q22 = 1 = 1Where:Where:

p is the frequency of the A allelep is the frequency of the A alleleq is the frequency of the a alleleq is the frequency of the a allele

if the values of p and q are known, we can if the values of p and q are known, we can calculate the frequency of the alleles AA, calculate the frequency of the alleles AA, Aa, and aa (and vice-versa)Aa, and aa (and vice-versa)

Limits to the Hardy-Weinberg Limits to the Hardy-Weinberg PrinciplePrinciple

Large populationsLarge populations

Random matingRandom mating

No mutationsNo mutations

No migrationNo migration

No natural selection against any of the No natural selection against any of the phenotypesphenotypes

Application of the Hardy-Application of the Hardy-Weinberg PrincipleWeinberg Principle

In a population, we know that a dominant In a population, we know that a dominant trait is present 82% of the time. Determine trait is present 82% of the time. Determine the percentage of individuals that make up the percentage of individuals that make up each genotype.each genotype.

The Hardy-Weinberg & Population The Hardy-Weinberg & Population ChangeChange

If a gene pool changes over time, one of If a gene pool changes over time, one of the 5 conditions it is based on must also the 5 conditions it is based on must also have changedhave changedTherefore, the strength of this principle is Therefore, the strength of this principle is to determine whether or not a population is to determine whether or not a population is evolvingevolvingThe Hardy-Weinberg equation also allows The Hardy-Weinberg equation also allows us to determine what percentage of a us to determine what percentage of a population are “carriers” of a traitpopulation are “carriers” of a trait

Evolutionary ChangeEvolutionary Change

gene pools are unstablegene pools are unstable

factors that bring about evolutionary factors that bring about evolutionary change are mutation, genetic drift, and change are mutation, genetic drift, and migration (or gene flow)migration (or gene flow)

MutationMutation

Gene FlowGene Flow

Non-Random MatingNon-Random Mating

Genetic DriftGenetic Drift

The Founder EffectThe Founder Effect

New populations are often formed by only New populations are often formed by only a few individuals (Founders)a few individuals (Founders)

The founders will only carry part of the The founders will only carry part of the original gene pool from the populationoriginal gene pool from the population

Therefore, the new gene pool will be Therefore, the new gene pool will be limitedlimited

The Bottleneck EffectThe Bottleneck Effect

Starvation, disease, human activities, or Starvation, disease, human activities, or natural disasters can quickly reduce a natural disasters can quickly reduce a large populationlarge populationThe survivors only have a subset of the The survivors only have a subset of the alleles present before the disaster, and alleles present before the disaster, and therefore, the gene pool loses diversitytherefore, the gene pool loses diversityGene pool change caused by a rapid Gene pool change caused by a rapid decrease in population is known as the decrease in population is known as the bottleneck effectbottleneck effect

Examples of the Founder EffectExamples of the Founder Effect

““Blue Fugates”Blue Fugates”

Philadelphia AmishPhiladelphia Amish

Examples of the Bottleneck EffectExamples of the Bottleneck Effect

Northern Elephant SealsNorthern Elephant Seals

CheetahsCheetahs

Natural SelectionNatural Selection

Natural selection is the only process that Natural selection is the only process that leads directly to evolutionary adaptationleads directly to evolutionary adaptation

Recall that natural selection occurs in the Recall that natural selection occurs in the following order:following order:

Advantage & Natural SelectionAdvantage & Natural Selection

Sexual Selection:Sexual Selection:

Heterozygote Advantage & Lethal Alleles:Heterozygote Advantage & Lethal Alleles:

Human Activities & Genetic Human Activities & Genetic DiversityDiversity

Humans can affect genetic diversity of Humans can affect genetic diversity of populations in many ways:populations in many ways:

1.1. Habitat fragmentationHabitat fragmentation

2.2. Unregulated hunting & habitat removalUnregulated hunting & habitat removal

Biotechnology & Gene PoolsBiotechnology & Gene Pools

We can use many techniques to modify We can use many techniques to modify organisms and the gene pools of organisms and the gene pools of populationspopulations

We now have added genes to species that We now have added genes to species that come from completely different species, come from completely different species, thereby adding a gene to a gene pool that thereby adding a gene to a gene pool that most likely would never have been there most likely would never have been there otherwiseotherwise

These genes could be passed on to others These genes could be passed on to others in a populationin a population

This could ultimately affect the process of This could ultimately affect the process of natural selectionnatural selection

As well, because genes do not work alone As well, because genes do not work alone (often they work together), the positive (often they work together), the positive effect of the inserted genes may be effect of the inserted genes may be negated because the gene affects other negated because the gene affects other traits necessary for survivaltraits necessary for survival

Cloning to Save SpeciesCloning to Save Species

Cloning can be one way to preserve gene Cloning can be one way to preserve gene poolspools

Creating clones of endangered species Creating clones of endangered species could reverse the threat of extinctioncould reverse the threat of extinction

In 2000, a cloned Asian gaur (a rare ox-In 2000, a cloned Asian gaur (a rare ox-like mammal) was born in Iowa to a like mammal) was born in Iowa to a domestic cow that served as a surrogate domestic cow that served as a surrogate mothermother