Bioevolution Exam 2 Review

The equation: p + q = 1 is allele or genotype frequency?

Allele frequency

What is the equation for genotype frequency?

p² + 2pq + q² = 1

What is p and what is q for the allele frequency?

• p is the frequency of the dominant allele in the population

• q is the frequency of the recessive allele in the population

Define the terms of the genotype frequency equation.

• p² is the frequency of the homozygous dominant genotype (AA)

• 2pq is the frequency of the heterozygous genotype (Aa)

• q² is the frequency of the homozygous recessive genotype (aa)

How do we know if a population is in Hardy-Weinberg equilibrium?

We have to compare allele or genotype frequencies across time points. When allele and genotype frequency are equally then they are in equilibrium.

• the observed equals the expected

What are the 5 conditions that must be met for a population to be in Hardy-Weinberg?

• No natural selection

• No mutation

• No migration (gene flow)

• There must be random mating

• There must be an infinitely large population (no genetic drift)

What is genetic drift?

a. Changes in allele frequencies due to natural selection favoring beneficial traits

b. Random changes in allele frequencies that occur by chance, especially in small populations

c. Movement of alleles between populations through migration

d. The introduction of new alleles through mutation

Random changes in allele frequencies that occur by chance, especially in small populations

Why do we need a large population for Hardy-Weinberg?

A large population is required for Hardy-Weinberg equilibrium primarily to minimize the effects of genetic drift (random chance events) on allele frequencies.

What are 2 examples of genetic drift?

• Population bottlenecks: when a population suddenly shrinks

• Founder effects: when a small group starts a new population

In a population, allelic diversity contributes to:

a) Variation in genotypes among individuals

b) The number of species in the population

c) Only the physical appearance of organisms, not their DNA

d) Genotypes being identical across all individuals

Variation in genotypes among individuals

In a population, what is the main difference between alleles and genotypes?

a) Alleles are the physical traits you see, while genotypes are the DNA sequences.

b) Alleles are different versions of a gene, while genotypes are the combinations of alleles an individual has.

c) Alleles are only found in populations, while genotypes exist only in individuals.

d) Alleles and genotypes are the same thing; there is no difference.

Alleles are different versions of a gene, while genotypes are the combinations of alleles an individual has.

Which of the following conditions must be met for a population to remain in Hardy-Weinberg equilibrium?

a) Natural selection must favor heterozygotes

b) The population must be large with random mating and no evolutionary forces acting

c) Mutation must occur at a constant rate

d) Migration must balance selection

The population must be large with random mating and no evolutionary forces acting

A population shows genotype frequencies that differ from expected Hardy-Weinberg values. What can be concluded?

a) Evolution is occurring in the population

b) Allele frequencies must be equal

c) The population is undergoing random mating

d) The population size is infinite

Evolution is occurring in the population

Population genetics

The study of allele distributions and frequencies —> it tracks the fate of alleles in populations across generations

Muatation

Source of all variation

Natural Selection often ______ variation.

reduces

Genetic drift decreases variation due to _______ _______.

random chance

T/F: Gene flow moves variation from population to population.

True

Non-random mating changes how alleles are _______ between individuals

partitioned

What is a gene pool?

A population of sperm and eggs

The effects of genetic drift are most noticeable when the population is….

Small

How do we know how a mutation or migration effects a population? What equation do we use to calculate frequency for the next generation?

p’1 = (1-m)p1 + mp2 → population 1

p’2 = (1-m)p2 + mp1 → population 2

• m = mutation or migration rate

• p1 = current frequency of A1 allele

• p2 = current frequency of A2 allele

What is the effective population size (Ne)?

a.) The total number of individuals in a population

b.) The number of individuals that survive to adulthood

c.) The number of individuals that contribute genes to the next generation

d.) The number of offspring produced in a generation

The number of individuals that contribute genes to the next generation

The effective population size determines the strength of ________ _________.

genetic drift.

A smaller effective population size (Ne) means there is a _________ drift.

stronger

A ________ effective population (Ne) means that there is a weaker drift.

larger

The strength of drift is what equation?

1/2(Ne)

In what situation will drift dominate? Will this cause allele frequency to change randomly?

When selection is less than the strength of drift and the population is small. Yes, this will make allele frequency change randomly.

In what situation will selection dominate? What will happen to allele frequency then?

When selection is more than the strength of drift. This will lead to higher fitness and higher allele frequency.

If s = 0 what does this mean for selection?

No selection

Large s → strong selection → ? fitness (more/less)

more fitness

Small s → ___?__ selection → less fitness

weak

In a population where the effective population size (Ne) is 50, allele A1 is under positive selection at a strength of s = 0.001. The initial frequency of allele A1 is 0.01. What do you expect to happen to the frequency of allele A1 over time?

a.) It will increase

b.) It will decrease

c.) It will change randomly

d.) It will stay the same

It will change randomly → genetic drift is greater than selection

If a population has an initial allele frequency of p = 0.5 and the population is at HWE, what do you expect to observe if you sample the population 10 generations later?

a.) The allele frequency (p) will have increased.

b.) The allele frequency (p) will have decreased.

c.) The allele frequency (p) will remain the same.

d.) The allele frequency (p) will either increase or decrease, but you can’t tell which direction from the information given.

The allele frequency (p) will remain the same.

• It is Hardy-Weinberg so there is no evolution occurring which means that allele frequency has to be the same.

Genetic drift is ________ _________ in allele frequencies.

random changes

Drift is due to ___________ _________ of gametes or genotypes in their contribution to a population gene pool.

sampling error

_______ alone will result in evolution.

Drift

Drift leads to _________ among population. Changes in allele frequency due to drift happen _________ in different populations.

differentiation; independently

How does population size affect drift?

The smaller the population size the stronger the drift. It will affect the population more rapidly. → lose genetic diversity

However, in large populations they are likely to maintain genetic diversity at a higher level.

Gene flow is the addition of genes into a gene pool of one population from one or more other populations. What is migration?

Migration in an evolutionary sense is gene flow because they are interchangeable. This is the movement of alleles from one gene pool to another.

Migration rate is the measure of gene flow. Migration rate is the proportion of …..

migrants that contribute to the next generation

• m = # of migrants / total population

How will you know if evolution is occurring?

When migration/mutation rate is greater than 0 (m>0) and p1 does not equal to p2. → The allele frequency changes, it does not stay the same. The observed does not equal expected. However, if they are equal than there is no evolution happening.

Gene flow decreases genetic variability among populations, making them more ______. At equilibrium, change in p = 0 when p1 = p2.

similar

Gene flow is a __________ force. → makes 2 populations similar

homogenizing

2 examples of non-random mating is positive assortative mating and mating among genetic relatives. Define both

Positive assortative mating

• like mates with like (wrinkled w/ wrinkled)

Mating among genetic relatives

• inbreeding

What is the effect of inbreeding?

increases the homozygotes and decreases the heterozygotes. → decreases fitness (only genotype frequency is impacted)

F is the coefficient of ________ → probability that two alleles in an individual are identical-by-descent. (identical-by-descent is when two alleles came from the same ancestral allele in a previous)

inbreeding

What is p and what is q?

p is the allele frequency in adults of A1 allele.

q is the allele frequency in adults of A2 allele.

Inbreeding depression → ?

when the population mean fitness is decreased because of the expression of recessive alleles → lowers fitness and natural selection wipes out population

• mate with genetic relative

What is selection?

Selection is the nonrandom survival and reproduction of phenotypes and genotypes

T/F: Selection can potentially lead to evolution if the difference in reproductive success is tied to genetic variation

True

If selection is the only force acting on the population and the population is large, what will happen to q over time?

q will decrease

If the population is very small and multiple mechanisms of evolution are allowed to act on the population what will happen to q over time?

Random. Q could increase or decrease.

Natural selection

Differences in survival, viability, or fecundity caused by environment or genes

Sexual selection

Differences in reproductive success caused by mate choice

Artificial selection

Differences in reproductive success or survival based on human decisions about what phenotypes they like.

Darwin’s Theory of Evolution by Natural Selection

1. Individuals within a species are variable

2. Some of these variations are passed on to offspring

3. In every generation, more offspring are produced than can survive

4. The survival and reproduction is not random: the individuals who go on to survive and reproduce are those with the most favorable variations.

Fitness

refers to how well an individual survives and how many offspring it produces

Adaptation

a trait that increases fitness relative to those without the trait

relative fitness

the fitness of an individual, phenotype, or genotype compared with others in the population

average excess of fitness

how an individual allele contributes to an individual’s fitness

• can be used to predict how the frequency of the allele will change from one generation to the next

Natural selection is relatively ineffective in small populations, but it is more _______ in large population

powerful

pleiotropy

a single gene affects multiple traits

positive selection

selection that increases the frequency of alleles within a population

Negative selection

selection that decreases frequency of alleles within a population

Frequency Dependent Selection

The relative fitness of individuals depends on the phenotypes of others in the population

Directional selection

selection favors phenotypes at one end of the distribution (against values at the other end

Stabilizing selection

selection favors the average in the population (against the extremes)

Disruptive selection

selection favors both extremes in the population (against the average)

A graphical relationship between phenotype and fitness is what?

fitness function

The nature of selection

• Natural selection is NOT evolution – It’s one process that can lead to evolution

• Natural selection acts on individuals, but its consequences (evolution) occur in populations over time

• Natural selection acts on phenotypes, but evolution consists of changes in allele frequencies

• Natural selection is not “perfect” or “progressive.” It doesn’t lead to evolution of the “best” individual, because it’s not a conscious process thinking toward the future.

Which statement best describes an adaptation?

A. Any trait that helps an organism survive

B. Any trait that increases reproduction compared to other individuals in the population

C. Any trait that is genetically inherited

D. Any trait that evolved recently

B. Any trait that increases reproduction compared to other individuals in the population

A mutation causes a plant to produce slightly thicker leaves, allowing it to retain water better during drought. Plants with this mutation produce 20 seeds, while plants without the mutation produce 15 seeds. Is thicker leaves an adaptation in this environment?

A. Yes, because individuals with the trait have higher fitness than those without it

B. Yes, because thicker leaves always improve plant survival

C. No, because the difference in seed number is small

D. No, because all plants survive

A. Yes, because individuals with the trait have higher fitness than those without it

In a population of beetles:

• Green beetles produce 10 offspring

• Brown beetles produce 12 offspring

Which statement is correct?

A. Both traits are adaptations

B. Green coloration is an adaptation

C. Brown coloration is an adaptation

D. Neither trait is an adaptation

C. Brown coloration is an adaptation — it has higher fitness

A population of birds evolves longer wings that improve flight efficiency. However, all individuals in the population now have long wings. Which statement is correct?

A. Long wings are not an adaptation because there is no variation

B. Long wings are an adaptation because they increased fitness relative to the ancestral trait

C. Long wings are not an adaptation because they do not affect reproduction

D. Adaptations must be rare traits

B. Long wings are an adaptation because they increased fitness relative to the ancestral trait

Why can gene duplication promote the evolution of new adaptations?

A. It increases mutation rate in the genome

B. One copy can maintain the original function while the other evolves a new one

C. It prevents harmful mutations

D. It eliminates nonfunctional genes

B. One copy can maintain the original function while the other evolves a new one

The globin gene family contains several genes that all bind oxygen but perform slightly different functions. What evolutionary process most likely produced these related genes?

A. Gene duplication

B. Horizontal gene transfer

C. Stabilizing selection

D. Genetic drift

A. Gene duplication

Two genes in the same species arose from a duplication event and now perform slightly different functions. What are these genes called?

paralogs

Why are many biological adaptations not perfectly designed?

A. Natural selection cannot improve traits

B. Mutations always reduce fitness

C. Adaptations evolve only in response to environmental change

D. Adaptations are modifications of structures inherited from ancestors

D. Adaptations are modifications of structures inherited from ancestors

Which scenario best demonstrates convergent evolution?

A. Two species inherit a trait from a shared ancestor

B. A gene duplicates within a genome

C. Two unrelated species independently evolve similar traits due to similar environments

D. A trait becomes more common through natural selection

C. Two unrelated species independently evolve similar traits due to similar environments

Two populations of stickleback fish independently evolve reduced body armor due to mutations in the same gene. This pattern is called:

A. Parallel evolution

B. Gene duplication

C. Stabilizing selection

D. Horizontal gene transfer

A. Parallel evolution

Why might proteins that can perform multiple functions be important in the evolution of new adaptations?

A. They prevent mutations from occurring

B. They allow natural selection to refine a secondary function

C. They eliminate the need for gene duplication

D. They reduce genetic variation

B. They allow natural selection to refine a secondary function

Complex adaptation

adaptation involving several genes and cis-regulatory elements. They experience selection together for a common function.

promiscuous proteins

Proteins that are capable of carrying out more than one function

Natural selection might favor mutation that improve protein’s ability to do the ______ ______. Proteins can also take on new function by gene duplication.

second function

Paralogs

homologous genes that arise by gene duplication

• Form gene families

Gene Duplication

If you’ve got 2 copies of a gene via duplication, one can perform the original task, while the other is free to evolve a new one

____-_______ regions of paralogs can evolve

• This can alter the conditions under which the gene is expressed

• Expressed in a new organ

• Expressed in response to a new signal

• Added to different network of genetic interactions (aka gene recruitment)

Cis-regulatory

gene family

a set of loci derived from a duplication of a single ancestral locus

• Typically have related functions because they come from a common origin

Examples of gene families

• Globin genes – all encode proteins that have hemebinding domain and can bind oxygen

• Immuoglobin superfamily

• Ribosomal RNA genes

• Olfactory receptors

Gene duplication happens ________ speciation event

before

What happens to gene duplicates after they arise?

1. One copy remains functional, while the other becomes nonfunctional (pseudogene)

2. Diverge in sequence and function ( Neofunctionalization & Subfunctionalization)

3. Gene conversion: sequence information from one locus transferred to other members of the gene family → concerted evolution

Loss of function

pseudogenes → non-functional DNA that is no longer translated into working proteins

Neofunctionalization

one of the gene copies, mutates, and takes on an entirely different, new function

How do we know:

• sequence similarity

• proteins have different functions but have the same sequence

Subfunctionalization

original copy of gene may have been performing more than one function

Horizontal Gene Transfer:

• Gene transfer between organisms (not inheritance)

• Common in bacteria/archaea

• Adds new genes for adaptation

• Genes may integrate into existing pathways

• Can occur via symbiosis (cell within a cell)

Example: antibiotic resistance

Imperfect Adaptations

• Adaptations are modifications of previously existing structures

• As such, they are constrained in the morphology that they can take on

• Therefore, many of them are flawed

Example: giraffe nerve (larynx) takes a long detour to the heart instead of a direct path

Convergent evolution

the process by which similar traits evolve in unrelated lineages

Example:

• Sharks are fish

• Dolphins are mammals

• They evolved similar streamlined bodies and fins

• This is because both adapted to swimming efficiently in water

Parallelism

convergent evolution that results from mutations to the same genes in different lineages

Example: reduction in numbers of spines in sticklebacks due to lack of predators