BIOCH17
POWERPOINT OUTLINE
NAME_____________________________
Chapter 17 Population Genetics and Speciation
ESSENTIAL QUESTIONS
How is microevolution studied?
How is phenotypic variation measured?
How are genetic variation and change measured?
How does genetic variation originate?
POPULATION GENETICS
How is microevolution studied?
Microevolution can be studied by observing changes in the numbers and types of alleles in populations.
The study of microevolution in this sense is ________________________ genetics.
GENETICS AND EVOLUTION
Charles Darwin knew that heredity influences characteristics, but he did know about _______________.
We can now study and predict genetic variation and change that underlie evolution.
MICROEVOLUTION
Microevolution or ____________________________________ is evolution at the level of genetic change in populations.
The study of genetics and evolution are advancing together.
The link from microevolution to macroevolution—__________________________________—can be studied in detail.
PHENOTYPIC VARIATION
How is phenotypic variation measured?
Biologists study polygenic phenotypes by measuring each _____________________________ in the population and then
analyzing the distribution of the measurements.
The variety of phenotypes that exists for a given characteristic depends on how many genes affect it.
PHENOTYPIC VARIATION
______________________________ traits or characters are influenced by several genes. Examples include human eye color
and height.
A distribution is an overview of the relative frequency and range of a set of values.
Often, some values in a range are more common than others.
A normal distribution, or _______________________ curve, is one that tends to cluster around an average value in the center
of the range.
MEASURING VARIATION AND CHANGE
How are genetic variation and change measured?
Genetic variation and change are measured in terms of the _________________________________ in the gene pool of a
population.
A frequency is the proportion or ratio of a group that is of one type. To study genetic change, the frequency of each allele in a
population can be tracked over time.
The particular combination of alleles in a population at any one point in time makes up a gene pool.
What is the ALLELE Frequency of the “b” eye color gene in your class??
SOURCES OF GENETIC VARIATION
How does genetic variation originate?
The major source of new alleles in natural populations is ______________________________________ in gametes or “germ
cells.”
Evolution cannot proceed if there is no variation.
Mutation generates new alleles at a slow rate.
Only mutations in germ cells (egg and sperm) are passed on to offspring.
Section 2: Genetic Change
KEY IDEAS
What does the Hardy-Weinberg principle predict?
How does sexual reproduction influence evolution?
Why does population size matter?
What are the limits of the force of natural selection?
What patterns can result from natural selection?
EQUILIBRIUM AND CHANGE
What does the Hardy-Weinberg principle predict?
The Hardy-Weinberg principle predicts that the frequencies of alleles and genotypes in a population will NOT change unless at
least one of five forces acts upon the population.
The forces that can act against _______________________________________________ are gene flow, nonrandom mating,
genetic drift, mutation, and natural selection.
HARDY WEINBERG EQUILIBRIUM
A population in which no genetic change occurred would be in a state of genetic equilibrium.
Genetic change in a population can be measured as a change in genotype frequency or
________________________________________-_.
A change in one doesn’t necessarily mean a change in the other.
THE 5 CONDITIONS OF HARDY WEINBERG EQUILIBRIUM
1. NO GENE FLOW
Gene flow occurs when genes are added to or removed from a population.
Gene flow can be caused by ______________________________________, the movement of individuals from one
population to another.
2. NONRANDOM MATING
In sexually reproducing populations, any limits or preferences of _____________________ choice will cause
nonrandom mating.
3. NO GENETIC DRIFT
Chance events can cause rare alleles to be lost from one generation to the next, especially when populations are small.
Such random effects on allele frequencies are called genetic drift.
4.NO MUTATION
Mutation can add a new _________________________ to a population.
5. NO NATURAL SELECTION
Natural selection acts to eliminate individuals with certain traits from a population.
As individuals are eliminated, the alleles for those traits may become less frequent in the population.
Thus, both allele and genotype frequencies may change.
SEXUAL REPRODUCTION AND EVOLUTION
How does sexual reproduction influence evolution?
Sexual reproduction creates the possibility that mating patterns or __________________________ can influence the gene pool
of a population.
For example, in animals, females sometimes select mates based on the male’s size, color, ability to gather food, or other
characteristics.
This kind of behavior is called sexual selection and is an example of nonrandom mating.
SEXUAL REPRODUCTION AND EVOLUTION
Another example of nonrandom mating is _______________________________, in which individuals either self-fertilize or
mate with others like themselves.
Inbreeding is more likely to occur if a population is small. In a small population, all members are likely to be closely related.
POPULATION SIZE AND EVOLUTION
Why does population size matter?
Allele frequencies are more likely to remain stable in _________________________ populations than in small populations.
Population size strongly affects the probability of genetic change in a population.
Genetic drift is a strong force in small populations and occurs when a particular allele
__________________________________.
NATURAL SELECTION AND EVOLUTION
What are the limits of the force of natural selection?
Natural selection acts only to change the relative frequency of alleles that exist in a population. It acts on genotypes by
removing ________________________________ phenotypes from a population.
NATURAL SELECTION AND EVOLUTION
Natural selection is a result of the following facts:
–All populations have genetic variation.
–Individuals tend to produce more _____________________________________ than the environment can support.
–Populations depend upon the reproduction of individuals.
GENETIC RESULTS OF SELECTION
The result of natural selection is that each allele’s frequency may increase or decrease depending on the allele’s effects on
survival and reproduction.
Although natural selection is not the only force that can cause evolution, it is a powerful force.
WHY SELECTION IS LIMITED
The key lesson that scientists have learned about evolution by natural selection is that the
________________________________
does the selecting.
Only characteristics that are expressed can be targets of natural selection. If a mutation results in rare recessive alleles, for
example, selection cannot operate against it.
For this reason, genetic disorders (such as cystic fibrosis in humans) can persist in populations.
PATTERNS OF NATURAL SELECTION
What patterns can result from natural selection?
Three major patterns are possible in the way that natural selection affects the distribution of polygenic characters over time.
These patterns are Directional selection, Stabilizing selection, and Disruptive selection
Directional Selection
In directional selection, the “peak” of a normal distribution moves in one direction along its range.
In this case, selection acts to eliminate on extreme from a range of phenotypes, making them less common.
Stabilizing Selection
In stabilizing selection, the bell-curve shape becomes ________________________________.
In this case, selection eliminates individuals that have alleles for any extreme type.
Stabilizing selection is very common in nature.
Disruptive Selection
In disruptive selection, the bell curve is “disrupted” and pushed apart into ___________________ peaks.
In this case, selection acts to eliminate individuals with average phenotype values.
Section 3: Speciation
KEY IDEAS
How can species be defined?
How do we know when new species have been formed?
Why is studying extinction important to understanding evolution?
DEFINING SPECIES
A species is generally defined as a _______________________________ that can interbreed and usually produce fertile
offspring.
Other definitions for species may be used for fossils or for organisms that reproduce asexually. Species may be instead be
defined based on their physical features, their ecological roles, and their genetic relatedness.
FORMING NEW SPECIES
How do we know when new species have been formed?
Speciation has occurred when the net effects of evolutionary forces result in a population that has unique features and is
_____________________________________ isolated.
SPECIATION
Each population of a single species lives in a different place.
In each place, natural selection acts upon each population and tends to result in offspring that are better adapted to each specific
environment.
If the _________________________________________ differ, the adaptations may differ. This is called divergence and can
lead to the formation of new species.
Speciation is the process of forming new species by evolution from preexisting species
REPRODUCTIVE ISOLATION
Reproductive isolation is a state in which two populations can no longer interbreed
From this point on, the groups may be subject to different forces, so they will tend to diverge over time.
Through divergence over time, populations of the same species may differ enough to be considered
____________________________.
Subspecies are simply populations that have taken a step toward speciation
REPRODUCTIVE ISOLATION
Any of the following mechanisms may contribute to the reproductive isolation of populations:
Geography
Ecological Niche
Mating Behavior and Timing
Polyploidy
Hybridization
EXTINCTION: THE END OF SPECIES
Why is studying extinction important to understanding evolution?
The species that exist at any time are the net result of both speciation and extinction.
Extinction occurs when a species fails to produce any more descendants. Extinction, like speciation, can only be detected after
it is complete.
EXTINCTION THE END OF SPECIES
More than 99% of all of the species that have ever lived becoming extinct.
Many cases of extinction are the result of _____________________________________________ change.
If a species cannot adapt fast enough to changes, the species may be driven to extinction.
BIO CH17 VOCABULARY REVIEW
Chapter 17 Population Genetics and Speciation
MICROEVOLUTION: the study of changes in allele frequency of a population
POPULATION: A group of organism of the same species that are breeding
PHENOTYPIC VARIATION: the allele frequencies within a population
NORMAL DISTRIBUTION: the bell curve
ALLELE FREQUENCY: the ratio of specific alleles in a population
GENETIC VARIATION: the different forms of alleles and traits in a population
HARDY WEINBERG EQUILIBRIUM: IS an IDEAL condition (IMPOSSIBLE) in which no evolution or allele
frequency change occurs (EQUILIBRIUM)- when all of the following DO NOT HAPPEN
GENE FLOW: the gain or loss of new alleles through immigration or emmigration
MUTATION: change in DNA sequence
NONRANDOM MATING: reproductive selection, females choose mates selectively
GENETIC DRIFT: small populations can have major changes in allele frequency
NATURAL SELECTION: when the environment favors a particular allele over another
FOUNDER EFFECT: the initial alleles/individuals in a population have great effect on allele frequency
POPULATION SIZE: the larger the population the smaller the impact of individual changes in allele frequency
SPECIATION: the development of new species through directional, disruptive or stabilizing selection
REPRODUCTIVE ISOLATION: a barrier to reproduction amoung individuals that leads to new species
Geography: physical barriers like rivers, canyons, oceans –squirrels in grand canyon
Ecological Niche: organisms are performing different roles in an ecosystem – Darwin Finches
Mating Behavior and Timing: migrations, mating dances in birds
Polyploidy: changes in chromosome number
Hybridization : pairings between similar species- liger
PENNSYLVANIA STATE STANDARDS: EVOLUTION
BIO.B.3.1.1: Explain how natural selection can impact allele frequencies of a population.
BIO.B.3.1.2: Describe the factors that can contribute to the development of new species (isolating mechanisms, genetic
drift, founder effect, migration).
BIO.B.3.1.3: Explain how genetic mutations may result in genotypic and phenotypic variations within a population.
BIO.B.3.2.1: Interpret evidence supporting the theory of evolution (fossil, anatomical, physiological, embryological,
biochemical, and genetic code).
BIO.B.3.3.1: Distinguish among the scientific terms: hypothesis, inference, law, theory, principle, fact, and observation.
BIO.B.1.2.1: Describe how the process of DNA replication results in the transmission and/or conservation of genetic
information.