Laboratory Exercise 2:
Microevolution and the Hardy-Weinberg
Principle
Biology II Laboratory BSC1011L Authors BJ AG NB AN SF JR BE Date: 8Jan2024
Material is also covered in Chapter 23 of Campbell Biology, 12th Ed.,
Urry, Cain, Wasserman, Minorsky and Orr.
Group Members: _______________________________________, ________________________________________
___________________________________________________, ___________________________________________
KEY CONCEPTS:
1. Evolution occurs within populations. Microevolution is defined by, and measured as, the change in allele
frequencies within and among populations. Genetic changes result in changes in phenotype. Evolution can be seen
in the changes in phenotypes through time. Evolution is a solid scientific theory, a summation of many laws.
2. The Hardy-Weinberg equilibrium principle states that under specific conditions allele frequencies:
• will reach equilibrium (in one generation).
• will stay at those equilibrium frequencies from one generation to the next until conditions change.
3. Given the Hardy-Weinberg equations (p+q=1, p2+2pq+q2=1) and the allele frequencies of an initial population,
one can predict the allele frequencies of the next generation if NO evolution occurs.
4. Five forces will change a population’s phenotype and allele frequencies allowing the population to evolve. The
greater the force on the population, the larger the change in allele frequencies.
• Mutations are random, and largely neutral or harmful, but occasionally a new mutation is beneficial and
results in a new adaptation. Mutations provide new alleles.
• During natural selection, the natural variation among individuals within a population of organisms results
in differences in their ability to survive and reproduce. Traits that increase the chance of survival and/or
reproduction are adaptations. Adaptive alleles increase in frequency, non-adaptive alleles decrease.
• Gene flow is the movement of alleles into or out of the population in the form of migration and can change
allele frequencies in complex ways. Immigration is the movement of alleles into a population, emigration
is the movement of alleles from a population.
• Nonrandom mating is also known as assortative mating sometimes due to sexual selection. When mates
deliberately chose each other, strong or weak changes in allele frequencies can occur.
• Drift includes various evolutionary events, all of which change allele frequencies due to random events.
The bottleneck effect and founder effect can cause dramatic changes in allele frequencies in small
populations.
Lab2: Exploring Hardy-Weinberg Equilibrium
5. Evolution is a change in allele frequencies due to complex forces. It is not forward looking, it does not choose what
will evolve. It does not lead to perfection, environments continually change so what is good in one environment may
be poor in another. Evolution can only build on pervious traits.
SKILLS YOU SHOULD MASTER BY THE END OF LAB:
1. Be able to calculate genotype frequencies, phenotype frequencies, and allele frequencies from population data.
2. Be able to list the assumptions under which a population will reach Hardy-Weinberg Equilibrium.
3. Be able to list and describe the factors that affect allele frequencies including mutation, natural selection, gene flow,
drift and non-random mating.
4. Know the Hardy-Weinberg equations and how to apply them to show change in populations.
5. Be able to answer questions on key concepts of microevolution (answered in this and all Lab 2 Handouts)
VOCABULARY:
Microevolution Natural selection Bottleneck effect
Hardy-Weinberg Equilibrium Principle Adaptation Stasis
p+q=1 Gene Flow Evolution
p2+2pq+q2=1 Immigration/emigration Hypotheses
Population Non-random mating Laws
Gene Pool Genetic Drift Theory (Scientific)
Mutation Founder effect
1
, I. Evolution
Evolution occurs in populations, not in individuals. Single individuals can develop or change in their lifetimes,
they can change due to their environment, but their alleles remain the same. Populations are groups of
interbreeding organisms and have properties that single individuals do not. These include the ability to reproduce
sexually, form social groups, and undergo biological evolution.
Evolution is Possible Because of Variation.
Organisms within populations vary in their phenotypes, or physical makeup. Those differences in phenotype are
in part due to genetic differences.
Evolution is Possible Because of Heritable Genetic Variation.
Individual organisms differ in their genetic makeup because they inherited different alleles for specific genes. For
example, a population of mice might carry both an allele for brown color fur (B) and an allele for light fur (b).
While every individual caries two alleles, the gene pool, or genetic make-up of a population, is described by:
• allele frequencies-the proportions of the alleles, B and b
• genotype frequencies-the proportions of different combinations of those alleles, BB, Bb, bb
• phenotype frequencies-the proportions of different forms
Evolution works on the phenotype and can be seen in the changes of the phenotype through time.
As diversity increase among groups, speciation, or the splitting of one species into two, can occur.
Microevolution is the change of allele frequencies in a population. If the allele
frequencies change, the population has evolved. The grand diversity of life that we see, and
that you will be studying this semester, is due to the many small changes, both random (e. g.,
segregation of alleles in gamete formation) and nonrandom (natural selection). Charles Darwin
recognized how magnificent this process was in his book On the Origin of Species (1859) and
he ended his book with:
“There is grandeur in this view of life, with its several powers, having been
originally breathed into a few forms or into one; and that, whilst this planet has
gone cycling on according to the fixed law of gravity, from so simple a Figure 1. Charles
beginning endless forms most beautiful and most wonderful have been, and are Darwin
being, evolved.” http://en.wikiquote.org/wiki/File:D
arwin.jpg
Is there time for small changes in evolution (microevolution) to result in the larger changes we see among the species
around us? Let’s calculate how long it would take to see a significant change in phenotype
Lab2: Exploring Hardy-Weinberg Equilibrium
Suppose the body size of a beetle can increase by 0.005 cm every generation and each generation lasts one year.
How many years would it take for the population to increase in size by 1 cm? _______
Suppose that beetle size was not constrained by the physiology needed to get oxygen to each cell.
How large could beetles grow in 300,000 years? _____________
Scientific Inquiry: Hypotheses, Laws, and Theories
In science a hypothesis is a best guess that is testable. Scientific laws identify patterns in nature that are
consistent, like Mendel’s first and second laws of inheritance. Laws may not have explanations; they are simply
observations.
A scientific theory is an explanation of a pattern that has been so thoroughly tested that most scientists agree on it
and consider it to be true and correct. A theory will be developed from laws as new information is discovered. For
example, Mendel’s laws were more thoroughly explained after the discovery of chromosomes, genes, and alleles
and were developed into the theory of inheritance.
Evolution is a scientific theory. Evolution is more than a hypothesis; it is more than a scientific law. It is an
entire body of knowledge for which there are many lines of evidence. It provides an explanation for the diversity
of form and function that we see in the biological world. It is the foundation for all biological studies. 2
Microevolution and the Hardy-Weinberg
Principle
Biology II Laboratory BSC1011L Authors BJ AG NB AN SF JR BE Date: 8Jan2024
Material is also covered in Chapter 23 of Campbell Biology, 12th Ed.,
Urry, Cain, Wasserman, Minorsky and Orr.
Group Members: _______________________________________, ________________________________________
___________________________________________________, ___________________________________________
KEY CONCEPTS:
1. Evolution occurs within populations. Microevolution is defined by, and measured as, the change in allele
frequencies within and among populations. Genetic changes result in changes in phenotype. Evolution can be seen
in the changes in phenotypes through time. Evolution is a solid scientific theory, a summation of many laws.
2. The Hardy-Weinberg equilibrium principle states that under specific conditions allele frequencies:
• will reach equilibrium (in one generation).
• will stay at those equilibrium frequencies from one generation to the next until conditions change.
3. Given the Hardy-Weinberg equations (p+q=1, p2+2pq+q2=1) and the allele frequencies of an initial population,
one can predict the allele frequencies of the next generation if NO evolution occurs.
4. Five forces will change a population’s phenotype and allele frequencies allowing the population to evolve. The
greater the force on the population, the larger the change in allele frequencies.
• Mutations are random, and largely neutral or harmful, but occasionally a new mutation is beneficial and
results in a new adaptation. Mutations provide new alleles.
• During natural selection, the natural variation among individuals within a population of organisms results
in differences in their ability to survive and reproduce. Traits that increase the chance of survival and/or
reproduction are adaptations. Adaptive alleles increase in frequency, non-adaptive alleles decrease.
• Gene flow is the movement of alleles into or out of the population in the form of migration and can change
allele frequencies in complex ways. Immigration is the movement of alleles into a population, emigration
is the movement of alleles from a population.
• Nonrandom mating is also known as assortative mating sometimes due to sexual selection. When mates
deliberately chose each other, strong or weak changes in allele frequencies can occur.
• Drift includes various evolutionary events, all of which change allele frequencies due to random events.
The bottleneck effect and founder effect can cause dramatic changes in allele frequencies in small
populations.
Lab2: Exploring Hardy-Weinberg Equilibrium
5. Evolution is a change in allele frequencies due to complex forces. It is not forward looking, it does not choose what
will evolve. It does not lead to perfection, environments continually change so what is good in one environment may
be poor in another. Evolution can only build on pervious traits.
SKILLS YOU SHOULD MASTER BY THE END OF LAB:
1. Be able to calculate genotype frequencies, phenotype frequencies, and allele frequencies from population data.
2. Be able to list the assumptions under which a population will reach Hardy-Weinberg Equilibrium.
3. Be able to list and describe the factors that affect allele frequencies including mutation, natural selection, gene flow,
drift and non-random mating.
4. Know the Hardy-Weinberg equations and how to apply them to show change in populations.
5. Be able to answer questions on key concepts of microevolution (answered in this and all Lab 2 Handouts)
VOCABULARY:
Microevolution Natural selection Bottleneck effect
Hardy-Weinberg Equilibrium Principle Adaptation Stasis
p+q=1 Gene Flow Evolution
p2+2pq+q2=1 Immigration/emigration Hypotheses
Population Non-random mating Laws
Gene Pool Genetic Drift Theory (Scientific)
Mutation Founder effect
1
, I. Evolution
Evolution occurs in populations, not in individuals. Single individuals can develop or change in their lifetimes,
they can change due to their environment, but their alleles remain the same. Populations are groups of
interbreeding organisms and have properties that single individuals do not. These include the ability to reproduce
sexually, form social groups, and undergo biological evolution.
Evolution is Possible Because of Variation.
Organisms within populations vary in their phenotypes, or physical makeup. Those differences in phenotype are
in part due to genetic differences.
Evolution is Possible Because of Heritable Genetic Variation.
Individual organisms differ in their genetic makeup because they inherited different alleles for specific genes. For
example, a population of mice might carry both an allele for brown color fur (B) and an allele for light fur (b).
While every individual caries two alleles, the gene pool, or genetic make-up of a population, is described by:
• allele frequencies-the proportions of the alleles, B and b
• genotype frequencies-the proportions of different combinations of those alleles, BB, Bb, bb
• phenotype frequencies-the proportions of different forms
Evolution works on the phenotype and can be seen in the changes of the phenotype through time.
As diversity increase among groups, speciation, or the splitting of one species into two, can occur.
Microevolution is the change of allele frequencies in a population. If the allele
frequencies change, the population has evolved. The grand diversity of life that we see, and
that you will be studying this semester, is due to the many small changes, both random (e. g.,
segregation of alleles in gamete formation) and nonrandom (natural selection). Charles Darwin
recognized how magnificent this process was in his book On the Origin of Species (1859) and
he ended his book with:
“There is grandeur in this view of life, with its several powers, having been
originally breathed into a few forms or into one; and that, whilst this planet has
gone cycling on according to the fixed law of gravity, from so simple a Figure 1. Charles
beginning endless forms most beautiful and most wonderful have been, and are Darwin
being, evolved.” http://en.wikiquote.org/wiki/File:D
arwin.jpg
Is there time for small changes in evolution (microevolution) to result in the larger changes we see among the species
around us? Let’s calculate how long it would take to see a significant change in phenotype
Lab2: Exploring Hardy-Weinberg Equilibrium
Suppose the body size of a beetle can increase by 0.005 cm every generation and each generation lasts one year.
How many years would it take for the population to increase in size by 1 cm? _______
Suppose that beetle size was not constrained by the physiology needed to get oxygen to each cell.
How large could beetles grow in 300,000 years? _____________
Scientific Inquiry: Hypotheses, Laws, and Theories
In science a hypothesis is a best guess that is testable. Scientific laws identify patterns in nature that are
consistent, like Mendel’s first and second laws of inheritance. Laws may not have explanations; they are simply
observations.
A scientific theory is an explanation of a pattern that has been so thoroughly tested that most scientists agree on it
and consider it to be true and correct. A theory will be developed from laws as new information is discovered. For
example, Mendel’s laws were more thoroughly explained after the discovery of chromosomes, genes, and alleles
and were developed into the theory of inheritance.
Evolution is a scientific theory. Evolution is more than a hypothesis; it is more than a scientific law. It is an
entire body of knowledge for which there are many lines of evidence. It provides an explanation for the diversity
of form and function that we see in the biological world. It is the foundation for all biological studies. 2
