Population Genetics Chapter 16 17 Vocabulary Population a

Population Genetics Chapter 16 & 17

Vocabulary �Population- a group of individuals living in the same area that breed with each other.

Gene Pool �Gene poolcombination of genetic information from all of the individuals in the population.

What is Genetic Variation? �Differences in alleles of genes �Provides the raw material for natural selection Genetic variation occurs among populations

Sources of Genetic Variation 1. Mutations- �Changes in the DNA of the individual �If the mutation effects the individuals fitness it will effect the gene pool of the population 2. Gene Shuffling�Occurs during the production of gametes �Each chromosome moves independently during meiosis �Crossing over

Relative Frequency �The number of times that an allele occurs in the gene pool. • Relative 30 20 frequency has nothing to do with dominant and recessive • Evolution involves changes in populations over time

What is Evolution �How is Evolution measured? �Any change over time in the relative frequencies of alleles in a population �It is populations not individual organisms that can evolve over time

Allele frequencies/ Gene pool Change in relative frequency= evolution

Single Gene vs. Polygenic Traits �The number of phenotypes produced is based on the number of genes that control the trait Controlled by 1 gene produces 2 phenotypes Traits that are controlled by 2 or more genes more than 2 alleles for each trait

Natural Selection on Single-gene traits �Individuals either live or die based on their phenotype �A normally brown population of lizards experiences mutations that produce red and black lizards �What will happen to the population? �What if the red lizards stand out more? �What if the black lizards have an advantage over all other lizards?

Natural Selection on Single-gene traits What do you expect the lizard population will look like by generation 50? Explain

Natural Selection on polygenic traits �When fitness varies natural selection can act Three different ways that natural selection can affect the distribution of phenotypes �Directional Selection �Stabilizing Selection �Disruptive Selection

Directional Selection �What would cause this shift? �When individuals at one end of the curve have higher fitness �The range of phenotypes shifts as individuals fail to survive/reproduce

Stabilizing Selection �What causes the shift? �When individuals near the center of the curve have higher fitness then either end

Disruptive Selection �What would cause the shift? �When individuals at either end of the curve have higher fitness then individuals near the middle �Natural selection works hardest on the intermediate type

Genetic Drift �Genetic Drift the random change in allele frequencies based on chance �Some individuals reproduce more times then others � Leave behind more offspring �Has nothing to do with natural selection

Genetic Drift �Relative frequencies move towards those that reproduce more times in the population �Eventually all the individuals in the population will have the same traits

Genetic Drift �Genetic Drift is most common in small populations �In large populations there is a higher chance that individuals will find a mate �Genetic Drift leads to change in relative frequency and therefor evolution

Speciation Diversity of Life

Speciation �Formation of new species �Species: organisms that breed with one another and produce fertile offspring (share the same gene pool) Horse Mule Donkey �Caused by natural selection and chance events

How does speciation happen Shared gene pool Genetic Change in 1 individual Change spreads through the population through reproduction Division/Isolation amongst the population Population begins evolving independently

Reproductive Isolation �Division amongst the population �Population must become reproductively isolated for 2 new species to develop �Allows for mutations/ changes in the gene pool to happen independently 3 types of isolation mechanisms 1. Behavioral Isolation 2. Geographic Isolation 3. Temporal Isolation

Behavioral Isolation �Different behaviors stop the individuals from being attracted to one another �Different mating rituals � Song � Dance � Color pattern � Antler size

Geographic Isolation �Population becomes separated by a geographic barrier �River �Mountain �Bodies of water �Forests �The individuals cannot pass onto the other side of the barrier and therefore cannot mate

Founder Effect �A small group from a population branches off and forms a NEW population �Geographically isolated from the origninal • Individuals carry alleles in different relative frequencies then the original population

Human Influence on Geographic isolation • Man made structures create geographic isolation • Roads • Towns • River Dams

Temporal Isolation �Reproductions times differ �Organisms reproduce at specific times of the day or year �Plants (morning vs. night) �Animals (spring vs. summer vs. fall vs. winter)

Patterns of Evolution 17 -4

Microevolution �Small changes in a species that build over time �Accounts for closely related species

Macroevolution �Large-scale evolutionary patterns and process that occur over long periods of time Supports the idea of Common Decent

Punctuated Equilibrium �Patterns of long, stable periods interrupted by brief periods of more rapid change � 100, 000 1, 000 years �Changes come in spurts �Caused by �Geographic isolation �Migration �Mass extinctions

Gradualism �Small variations that are hard to notice over a short period of time �Variation takes place slowly (gradually)

Gradualism vs. Punctuated Equilibrium

Extinction �The end of a species or group of species �Natural selection causes extinction �Most common cause for extinction: �Species compete for limited resources �Environments change individuals can’t survive �Why is extinction necessary for evolution to continue? �video

Mass extinction �Mass extinction: many types of living things became extinct at the same time �A the end of the Paleozoic era many organisms died out � 95% of the complex life in the oceans disappeared �Not all organisms disappeared �Reason for mass extinction �Collapsing environment �Caused by multiple factors

�How did the extinction of the dinosaurs allow for the diversification of mammals?

Adaptive Radiation �A single species evolves into diverse forms that live in different ways

Convergent Evolution �Process in which unrelated organisms come to resemble each other (Analogous Structures) �“side effect” of adaptive radiation �Takes place among different species that live in similar ecological environments �Face similar environmental demands

Coevolution �The process where 2 species evolve in response to changes in each other �Evolutionary change in one organism induces change in the other �Flowers/pollinator �Predator/Prey

Genetic Equilibrium Hardy-Weinberg Principle

Population Genetics �Evolution is the change in frequencies of alleles in the gene pool of a population Parent Generation F 1 offspring Allele- B 92% 82% Allele- b 8% 18% �The gene pool has been shifted toward the “b” allele

Genetic Equilibrium �The situation in which allele frequencies stay the same with each new generation Parent Generation F 1 offspring Allele- B 92% Allele- b 8% 8% How likely is it that the allele frequencies will stay the same from one generation to the next?

Hardy-Weinberg principle �Allele frequencies in a population will stay constant unless one or more of the factors are violated �What are some conditions under which NO evolution will occur?

Maintaining equilibrium Genetic Equilibrium: 1. Random mating 2. Large population 3. No movement into or out 4. No mutations 5. No natural selection Each of these things can cause evolution to take place!

Random Mating �All individuals must have an equal opportunity to reproduce In nature is mating completely random? Why or why not?

Large populations �Large populations decrease the chances of genetic drift taking place �Why is genetic drift not as common in large populations?

No movement into or out �When individuals move into a population or out of it, the gene pool will change

No mutations What role do mutations play in evolution? �Mutations introduce new alleles into the population

No natural selection �Natural selection gives one phenotype the advantage over the other

Real Life? �Does the Hardy-Weinberg equilibrium exist in real life? 1. Random mating 2. Large population 3. No movement into or out 4. No mutations 5. No natural selection �Evolution is inevitable �In most populations evolution happens!