BIOL 001 - Exam 4
In your own words, define/describe genetic drift.
Change in allele frequencies due to random sampling of alleles - ALL populations are influenced by genetic drift at ALL times -allele frequencies of small populations are more likely to be significantly altered by genetic drift
Natural selection leads to organisms that are far from perfectly suited to their environment. Why? A) In some cases, natural selection favors traits that decrease an individual's fitness in their current environment. B) Not all adaptations are heritable. C)Adaptations are always beneficial under a wide range of environmental conditions. D)Natural selection is limited by the genetic variation in a population.
D) Natural selection is limited by the genetic variation in a population.
The ease with which humans travel around the world is likely to increase the effects of _____ on the human population. A) genetic drift B) gene flow C)natural selection D)mutations E)natural selection, gene flow, and genetic drift
B) gene flow
Describe two different scenarios in which a population could undergo rapid evolutionary change.
Bottleneck - Founder Effect -
Think about functions of HIV reverse transcriptase, cellular DNA polymerase, and cellular RNA polymerase. In what ways are these three enzymes similar? How are they different?
DNA polymerase - enzymes that synthesize DNA molecules from deoxyribonucleotides, the building blocks of DNA RNA polymerase - an enzyme that is responsible for copying a DNA sequence into an RNA sequence, during the process of transcription. HIV transcriptase - reverse transcription (copying HIV RNA genome into DNA); using an RNA template to form a complementary DNA strand; degrades (chops up) the RNA template and forms a DNA strand complementary to other DNA strand
Do you think artificial selection typically increases or decreases variation? Why?
Decreases variation; human influence tailors an organism/crop to what it exactly wants
Your friend tells you that polar bears evolved to have thick fur because it was necessary for them to survive in cold temperatures. Correct your friend's misunderstanding.
Environmental conditions (the cold weather) can change, so the species would not change that specific quality of themselves Evolution CANNOT purposefully create variation - acts on existing variation or variation that arises by random mutations
Is the statement "Dinosaurs became extinct because they could not evolve" true or false? Explain why.
Evolution does NOT have a goal -NOT headed towards a particular outcome -CANNOT purposefully create variation - acts on existing variation or variation that arises by random mutations AND Why can't evolutionary change lead to organisms that are perfectly suited to their environment? A. Genetic variation arises randomly in a population. B. Environmental conditions can change. C. A trait that is beneficial in some ways can have the potential to decrease an organism's ability to survive and reproduce in other ways. D. All of the above explain why evolution cannot lead to "perfect" organisms. -ALL OF THE ABOVE
HIV replicates rapidly. If HIV replicated more slowly, what effect, if any, would that have on the rate of HIV evolution?
I believe HIV would then evolve slower. If HIV replicated slower, the body's immune system would have more capabilities to ward off the virus, and then an HIV virion may not be able to attach to a host cell.
If the DNA copies of the HIV genome were NOT integrated into host cell chromosomes, could the HIV genes be transcribed and translated by the cell's enzymes? Why or why not?
I don't believe so, since the HIV virion requires the energy and resources of a host cell to thrive; also, integration of the HIV DNA genome allows HIV genes to be expressed using the host cell's enzymes and resources (molecules, energy)
Explain why "survival of the fittest" is NOT an appropriate way to define natural selection. Write a definition for natural selection using your own words.
In terms of evolution and biology, fitness has an entirely different meaning. Fitness is an individual's ability to successfully reproduce and have those offspring survive. For example, if a very strong lion sires one offspring, he is considered less fit compared to a physically very weak lion that sires ten offspring.
Which mechanism(s) of microevolution, if any, would be likely to increase genetic diversity (variation) in a population? Decrease genetic diversity? Explain your reasoning.
Increase = gene flow and mutations; these introduce new alleles into a population Decrease = also gene flow, genetic drift, mutations, artificial selection (can increase the frequencies of alleles that reduce an individual's ability to survive and reproduce)
If two populations have virtually identical allele frequencies, can gene flow between them lead to evolutionary change? Why or why not?
Magnitude of change depends on multiple factors - differences in allele and phenotype frequencies of the two populations - how many move and in what direction(s) - duration of movement (i.e. long-term vs. short-term)
Explain how gene flow can occur WITHOUT movement of individuals between populations. Is this possible for all species?
Movement of individuals OR gametes can affect the allele frequencies of populations -gene flow is best defined as movement of alleles between populations -movement of a whole population to an area where there are no others is NOT gene flow -formation of a new population is NOT gene flow
For each mechanism of microevolution, describe a hypothetical (or real) scenario other than the ones from class to illustrate how the mechanism acts to change the distribution of heritable phenotypes (allele frequencies) in a population. In each case explain how the mechanism of evolution causes the change.
Mutation - Gene Drift - Gene Flow - Sexual Selection - Natural Selection - Artificial Selection -
Describe the mechanisms (forces) that can lead to microevolution. Explain why mutations are important to consider even though they rarely cause significant changes in allele frequencies.
Mutations (-source of new alleles; rarely (if ever) cause significant changes in allele frequencies) Natural Selection (change due to differences in survival and reproduction) Artificial Selection (change due to human intervention) Sexual Selection (change due to differences in mate preferences) Genetic Drift (change due to random sampling of population (alleles)) Gene Flow (change due to movement between populations)
Explain why heritable differences in the phenotypes of organisms must be due to genetic differences. Why aren't all phenotypic differences heritable? Give an example of a phenotypic difference that is heritable and one that is not heritable.
PHENOTYPES are the physical expression/characteristics of GENOTYPES - therefore, heritable differences in phenotypes must come from genetic differences. Not all phenotypic differences are heritable due to the ENVIRONMENT around an individual/population; for example, the caterpillars on the PPT (what they ate affected their fur) Heritable Example - Coat color of oldfield mice
In one population of birds, females have very short tails and males have very long tails. In a population of a different species of birds, the tail lengths of males and females are both short. In which of the two populations do you predict sexual selection has a greater effect on tail length? Which trait is more likely to be suited to survival? Explain your answers.
Population of females w/ short tails and males w/ long tails, because the females may view the longer tails to be a more attractive quality in a mate, whereas in the other population, they are all the same
Explain why an understanding of the mechanisms of microevolution is important for scientists working to preserve endangered species. Why are small populations sizes such a big concern?
Small populations are a concern because they may have a limited genetic diversity, which leads to a high frequency in harmful alleles.
Explain why, once a cell is infected with HIV, the cell cannot get rid of the HIV genome.
The cell cannot rid itself of the HIV genome because the integrase (enzyme) integrates the HIV DNA into the host cell, which means that the host cell and its chromosomes are permanently altered.
Propose a hypothesis to explain why, when grown in the wild, many species of artificially selected plants have a lower relative fitness than wild varieties.
The selection of particular traits may reduce the ability of other traits to help the organism, and thus hinder its overall fitness
Why is it necessary for certain HIV enzymes (e.g. reverse transcriptase) to be present in the capsid, while the virus can rely on the cell's enzymes to produce other HIV proteins?
These HIV enzymes are coded to specifically chop up the RNA template and form a DNA strand complementary to the other present DNA strand.
In dry years, short grass in a field has a higher relative fitness than tall grass. In wet years, tall grass survives and reproduces better than short grass. Is this an example of stabilizing, disruptive, or directional selection? Explain your answer.
This is disruptive selection because the environment is favoring two extremes - the short grass has higher fitness in dry years, whereas long grass has higher fitness in wet years
In what ways are viruses different from one another? Are cells different from one another in any of these ways?
Viruses, due to their strains, infect different hosts (humans, animals, etc); may have either single/double stranded DNA or RNA genomes
A group of bears moves from one side of a mountain to join a different population of bears that lives on the other side of the mountain. Is this an example of gene flow? If so, why? If not, why not?
Yes, because there are two different populations present
Many species of plants produce sweet fruits to attract animals who eat the fruit and help promote seed (offspring) dispersal, which improves offspring survival of the plant. Production of fruits takes significant energy and resources, and plants that produce fewer fruits can live longer than those that produce more fruits. Could fruit production be considered an adaptation? Why or why not?
Yes, it could be considered an adaptation because it is increasing the # of seeds that will dispersed by other animals
What factors determine the relative fitness of an individual?
number of alleles an individual is able to pass on in relation to others in the population
Describe the basic steps of HIV's life cycle. Include the functions of the specific viral enzymes we discussed.
1. Attachment and entry 2. Reverse transcription (HIV transcriptase - copying HIV RNA genome into DNA) 3. Integration (insertion of HIV DNA genome into a chromosome)
The animation describes a population of beetles where shell color is determined by a single gene. In the population, there are brown shell alleles and green shell alleles. The green allele is dominant to the brown allele. A. the frequency of the brown shell color allele will increase. B. the frequencies of the brown and green shell color alleles are unlikely to change. C. the frequency of the green shell color allele will increase.
C. the frequency of the green shell color allele will increase.
Which of the following is an example of natural selection? A) A severe storm kills more green beetles than brown beetles. B) Green beetles migrate out of the population, and brown beetles migrate into the population. C) Green beetles migrate out of the population. D) Green beetles have more offspring than brown beetles because they are better at finding food. E) Green beetles and brown beetles always have the same number of offspring.
D) Green beetles have more offspring than brown beetles because they are better at finding food.
Give at least two reasons that evolution cannot lead to "perfect" organisms and use hypothetical (or real) examples to illustrate your reasons.
-Environmental conditions can change (so, if a polar bear had "grown" fur to deal with the cold, it would be of no use if the Arctic suddenly became hot) -Traits have trade-offs (a cheetah can be very fast, but is also not the best at climbing trees)
What is an adaptation? What evidence would you need to support the hypothesis that a trait is an adaptation in a particular species?
-adaptation: a heritable trait that increases an individual's relative fitness which traits are considered adaptations depends on environment AND can change with other evolutionary changes (see if the trait is stable over time - if it remains despite environmental change, then it's needed)
Explain why an individual (e.g. you) CANNOT evolve.
-an individual's genotype does not change over its lifetime (it's what you're born with) -mutations acquired during an individual's lifetime occur in specific cells, NOT in the whole organism
Describe the process by which HIV enters cells.
1) HIV envelope protein interacts with CD4 2) Interaction with CD4 allows HIV envelope protein to interact with CCR5 coreceptor 3) HIV envelope protein inserts into cell membrane 4) HIV envelope and cell membrane fuse 5) fusion allows HIV capsid to enter the cell
Explain why evolutionary change can increase the percentage of individuals in a population that have traits that are NOT beneficial for survival and reproduction.
A trait that is beneficial in some ways can have the potential to decrease an organism's ability to survive and reproduce in other ways.
Explain why viruses must enter cells to replicate (reproduce).
A virus requires the resources and energy of a host cell in order to reproduce
Select ALL statements that correctly describe evolutionary change. A) Evolution can change the allele frequencies in a population, but cannot alter an individual's allele frequencies. B) Heritable traits that are not beneficial for individuals within a population will be eliminated by the mechanisms of evolutionary change. C) If a heritable trait is beneficial, all mechanisms of evolutionary change will increase its frequency within a population. D)The distributions of heritable phenotypes in a population can be affected by multiple mechanisms of evolution at the same time.
A) Evolution can change the allele frequencies in a population, but cannot alter an individual's allele frequencies. D) The distributions of heritable phenotypes in a population can be affected by multiple mechanisms of evolution at the same time.
Select ALL statements below that correctly describe genetic drift. A) Genetic drift most often decreases genetic variation in populations where it significantly alters allele frequencies. B) Genetic drift can affect populations that are also influenced by other mechanisms of microevolution. C) Genetic drift can only alter allele frequencies in small populations. D) Genetic drift can cause evolutionary change in a single generation.
A) Genetic drift most often decreases genetic variation in populations where it significantly alters allele frequencies. B) Genetic drift can affect populations that are also influenced by other mechanisms of microevolution. D) Genetic drift can cause evolutionary change in a single generation.
Explain how artificial selection is different from natural selection.
Artificial Selection = change in allele frequencies due to human intervention Natural = NATURE!!
Explain why mutations, gene flow, and genetic drift CANNOT lead to adaptations.
-Mutations and gene flow are the ONLY two mechanisms that can introduce new alleles into a population -These mechanisms are random -NO mechanism of microevolution can cause a new trait (allele) to occur in a population for a particular purpose (evolution does NOT have a goal)
Review the statements that you marked as true or false. Make sure that you are confident that you know which ones are true, and that can appropriately correct/change the false statements.
1) An individual (e.g. you) evolves over the course of their lifetime. - FALSE 2) Organisms adapt to their environment, and pass these adaptations on to their offspring. 3) Evolution generates traits that allow organisms to survive and reproduce better. - NOT ALWAYS 4) A squirrel that lives for two years and has five offspring is more evolutionarily fit than a squirrel that lives to be nine years old and has three offspring. - TRUE; more offspring = more "fit" 5) Natural selection is best defined as survival of the fittest. - FALSE; fittest means most offspring, not the strongest 6) A trait that helps an organism survive and reproduce may not be beneficial for individuals in future generations. - TRUE 7) Evolutionary change can lead to organisms that are less well-suited to their environment - TRUE
Which of the following explains how evolutionary change affects the allele frequencies and trait distributions in populations? A) Evolutionary change alters the frequencies of alleles within a population, which can be observed as changes in the distribution of traits. B) In a population, evolutionary change alters either the allele frequencies or distribution of traits, but cannot affect both at the same time. C) The distribution of all traits within a population can be altered by evolutionary change, but the frequencies of some alleles cannot. D)The frequencies of alleles within a population can be altered by evolutionary change, but the trait distributions cannot.
A) Evolutionary change alters the frequencies of alleles within a population, which can be observed as changes in the distribution of traits
Male insects often produce noise (sing) while females of the same species do not. What is the most likely explanation for this pattern? A) Female insects are more likely to mate with males that sing a particular song. B) Singing makes an insect more noticeable to predators regardless of its sex, but natural selection has only acted on females. C) The ability to sing is favored by genetic drift in males of the species, but not females. D) Males that are able to sing live longer than males that cannot produce noise
A) Female insects are more likely to mate with males that sing a particular song. Sexual selection favors traits that improve an individual's chance of getting a mate, and therefore their chance of passing alleles on to the next generation. Traits favored by sexual section do NOT always improve an individual's ability to survive, and often decrease survival. Genetic drift cannot favor a particular trait, since genetic drift refers to changes in allele frequencies due to random chance. If a trait makes an individual less likely to survive (e.g. more likely to be eaten by predators), then natural selection will decrease the frequency of that trait in both sexes.
In a population of green and brown beetles where bird predators that eat green beetles are present, genetic drift: A) is more likely to affect a small population than a large population. B) will increase the frequency of brown shell color alleles in the population because brown beetles can better escape predators. C) will increase the frequency of the green shell color allele because it is the dominant allele. D) cannot affect the relative frequencies of green and brown shell color alleles because shell color allele frequencies will be affected by natural selection.
A) is more likely to affect a small population than a large population.
In the context of evolution, genetic variation is important because A) it provides a source of allele variation that may be beneficial if the environmental conditions change. B) it ensures that some individuals in a population will have the traits they need to survive. C) it allows an individual to pass on only the most beneficial alleles to its offspring. D) it gives individual organisms the ability to undergo evolutionary change during their lifetime.
A) it provides a source of allele variation that may be beneficial if the environmental conditions change. Mutations are an important source of new alleles in a population. Note that the variation introduced by crossing over, independent alignment of chromosomes, and random fertilization can also lead to new allele combinations that may affect the phenotype frequencies observed in populations of sexually reproducing organisms. Although genetic variation introduced by mutations can be (and frequently is) harmful, some mutations introduce new alleles that can be beneficial in the current environment or if environmental conditions change. Individuals CANNOT evolve, and which alleles are passed on to the offspring of an individual is entirely random due to the behavior of chromosomes in meiosis and random fertilization.
Which statement(s) correctly describe(s) adaptation? A) More complex organisms such as humans are better adapted than less complex organisms such as earthworms. B) A trait that is an adaptation may cease to be an adaptation if the environment changes. C) Adaptations arise because they are needed in particular environments. D) All of the above
B) A trait that is an adaptation may cease to be an adaptation if the environment changes.
Which of the following correctly describe(s) evolutionary change? A) Evolutionary change can only alter the distributions of traits that improve an individual's ability to survive and reproduce. B) Evolutionary change can only affect the distributions of traits that are passed from generation to generation (heritable). C) Evolutionary change cannot occur in a population in a single generation. D)All of the above
B) Evolutionary change can only affect the distributions of traits that are passed from generation to generation (heritable).
Which of the scenarios below, if any, illustrate artificial selection? A) Increased use of antibiotic drugs has led to an increased frequency of antibiotic resistant bacteria. B) Farmers allow only certain turkeys to mate, and farm-raised turkeys have more white meat and grow faster than turkeys that live in the wild. C) Scientists generate a mutation in a tomato plant gene that allows tomato plants to grow larger tomatoes. D) Pumpkins grown in soil containing fertilizer are bigger than pumpkins grown in soil that lacks fertilizer. E) All of the above F) None of the above
B) Farmers allow only certain turkeys to mate, and farm-raised turkeys have more white meat and grow faster than turkeys that live in the wild. Artificial selection is a change in allele frequencies due to humans choosing individuals with certain genetically determined traits as the parents of the next generation. Directly modifying genes and effects due to changing environmental conditions (by humans or as a result of natural causes) are NOT examples of artificial selection.
Give hypothetical (or real) examples of a population bottleneck and the founder effect. Explain why these scenarios usually change the allele frequencies in populations, why they are examples of genetic drift, and why they lead to situations in which there is an increased chance for genetic drift to lead to additional changes in allele frequencies.
Bottleneck: Haiti earthquake in 2010 killed off 80% of local jellyfish; there used to be 10 different kinds, now there's only 2 (just a made-up example) *less genetic diversity* Founder: portion of population moves and forms a new population; frequency of disease allele INCREASES Amish community in eastern PA founded by small group of German colonists, an unusually large proportion of which had more than five fingers.
How are stabilizing and disruptive selection different? A) With stabilizing selection, individuals with the extreme of a trait (e.g. very dark or very light fur) have high fitness. B) With disruptive selection, individuals with the extreme of a trait have low fitness. C) Stabilizing selection leads to adaptation. Traits favored in disruptive selection are not adaptations. D) Stabilizing selection reduces the amount of variation in a trait. Disruptive selection increases the amount of variation in a trait. E) With stabilizing selection, the "value" of a trait (e.g. whether flowers are larger or smaller) does not influence survival. With disruptive selection, the degree of a trait affects survival.
C) Stabilizing selection reduces the amount of variation in a trait. Disruptive selection increases the amount of variation in a trait. In stabilizing selection, organisms with an intermediate phenotype for a particular heritable trait have a higher fitness than organisms with "extreme" phenotypes for that trait. For example, if mouse fur color varied from white to black, gray mice would be better able to survive and reproduce than either white or black mice. Over time, the population would have a higher percentage of mice with gray fur, which would reduce the variation. With disruptive selection, two different heritable phenotypes are favored (i.e. both black mice and white mice both have higher fitness than gray mice), which will increase, or at least maintain, the variation in the population.
When assessing microevolutionary changes, why is it important to consider both trait distributions and allele frequencies? A) Some differences in traits are not due to genetic differences. B) Genetic differences (e.g. different alleles) do not always result in trait differences. C) The distribution of a particular heritable trait within a population could change without an alteration in allele frequencies. D) All of the above explain why it's important to consider both trait distributions and allele frequencies.
D) All of the above explain why it's important to consider both trait distributions and allele frequencies. The relationship between an organism's genotype (combination of alleles) and its phenotype (combination of physical and functional traits) is complex. Some genetic differences do not lead to differences in traits. For example, two alleles could have different DNA sequences but result in the same polypeptide due to the redundancy of the genetic code. Additionally, most traits can also be influenced by the environment. This leads to differences in traits between individuals that are NOT heritable. Finally, the same allele frequency can lead to different trait frequencies (like the mouse population we used as an example in class). Therefore, it is possible for the distribution of a particular trait to change in a population WITHOUT changing the allele frequency.
Which of the following, if any, accurately describe(s) evolution? A) Individuals undergo evolutionary change over their lifetimes, and these changes are seen as changes in the distribution of heritable phenotypes in populations. B) Evolutionary change cannot be observed because it requires many generations for evolution to cause significant changes in the distributions of heritable phenotypes in a population. C)Mutations are not considered a mechanism of evolutionary change because mutations occur randomly and may not be beneficial for an individual. D) All of the above E)None of the above
E) None of the above Although the mechanisms of evolution act on individuals (i.e. an individual passes on their alleles by having offspring or does not), an individual CANNOT evolve. In many cases, mechanisms of evolution can cause rapid evolutionary change. For example, when a group of individuals moves into a population that has significantly different allele frequencies compared to the "newcomers," this leads to an immediate change in the allele frequencies and most likely the phenotype frequencies as well. Although mutations don't cause significant changes in allele frequencies, they DO introduce new alleles and thus alter the pool of alleles present within a population. It is also important to remember that natural selection is NOT the only mechanism of evolutionary change. Some mechanisms, like mutations, do increase the frequencies of alleles in a population that are NOT beneficial for an individual.
HIV can undergo rapid evolutionary change. Based on what you know about the role of mutations in evolution, explain why the high error rate of reverse transcriptase plays an important role in the rapid evolution of HIV populations.
HIV reverse transcriptase has several mutations (remember the number line/scale from the powerpoint) HIV populations can evolve rapidly - reverse transcriptase is NOT very accurate - virus replicates (reproduces) rapidly - frequency of a particular mutation can increase quickly
Describe the structure of the HIV virion and explain how its genome is different from the genome of a cell.
Has an envelope (membrane), capsid (protein shell), HIV enzymes (3), RNA Genomes (2 copied) and HIV envelope proteins (required for attachment to cells) -mRNAs produced by expression of a gene can be spliced differently to generate different proteins in eukaryotic (e.g. human) cells. A few HIV mRNAs can be spliced differently. Most HIV polypeptides are cut after translation to generate multiple proteins
The influenza virus, which causes the flu, is similar to HIV in terms of its virion structure and the fact that its genome is RNA. Influenza viruses can infect epithelial (skin cells), but not T cells. Propose a hypothesis to explain why. Design a basic experiment (including controls!) to test your hypothesis.
Hypothesis: The protein receptors that the influenza virus can attach to are only on skin cells
If all the individuals in a population had identical genotypes, could the population evolve? If not, why not? If so, how?
It's possible for them to evolve; for example, if everybody was heterozygous for brown eyes (Bb), blue eyes (bb) could eventually arise.
Compare and contrast the mechanisms of microevolution. In what ways are they similar? How are they different?
Mutation - since any particular mutation is rare, this process alone cannot account for a big change in allele frequency over one generation Gene Drift - change in allele frequencies due to random sampling of alleles Gene Flow - change due to movement between populations) Sexual Selection - increases the frequencies of traits that improve an individual's chances of getting a mate; traits favored by sexual selection MUST increase attractiveness to opposite sex Natural Selection - change due to differences in survival and reproduction) Artificial Selection - change in allele frequency due to human intervention j
Some insects look very similar to the flowers of a particular species of plant present where they live. Their shape and coloration is considered an adaptation that improves their ability to hide from predators. If that species of plant suddenly disappeared, would the shape and coloration of the insects still be considered an adaptation? Why or why not?
No; adaptations also depend on a species' environment. If the plants are no longer included in the environment, then the insects would have nothing to camouflage into.
Do only the most fit individuals in a population pass their genes on to the next generation?
No; less fit individuals can still pass on their genes, but their offspring may be less likely to survive
Explain why traits favored in sexual selection do not always improve an individual's ability to survive.
Sexual selection could favor a trait that increased an individual's ability to reproduce, but decreased their ability to survive. Sexual selection increases the frequencies of traits that improve an individual's chances of getting a mate - traits favored by sexual selection MUST increase attractiveness to opposite sex - may DECREASE ability to survive
Review the sources of genetic variation in sexually reproducing organisms. What are the sources of genetic variation for prokaryotes?
Sexually reproductive organisms = independent orientation, crossing over, random fertilization Prokaryotes = genetic recombination, where genetic material of two organisms is combined, occurs in several ways, increasing variation. BOTH can experience mutations
Describe a scenario in which gene flow would significantly alter the allele frequencies of a population. Now describe a situation in which gene flow would have little to no effect on allele frequencies
Significant Effect: 1. Florida Panther example - the significant decrease in population size (bottleneck) resulted in limited genetic diversity and a high frequency harmful alleles. Litte/No Effect: 1. A population with high genetic diversity, and the majority of which all move in the same direction
Explain why the allele frequencies of ALL populations are influenced by genetic drift at ALL times. Explain why the allele frequencies of smaller populations are more likely to be significantly altered by genetic drift compared to larger populations.
Smaller populations will feel the consequences of genetic drift more drastically than larger populations (there's less people, so a greater likelihood that they'll be affected) frequencies of alleles are more stable from generation to generation when the population is large, but populations will not stay 100% constant with their allele frequencies due to the forces of microevolution
A population of lizards varies in heritable characteristics such as color, tree climbing ability, and ability to run on the ground. The primary predators of the lizards are birds and foxes. Use this scenario to describe a situation in which stabilizing selection would be observed. Under what conditions might directional selection be observed? Disruptive selection?
Stabilizing - color would be brown-green to blend in with the grass and the bark on trees; they are both moderate at tree climbing and running (not too good at either, because then that would be favoring the extreme) Directional - color would be either green or brown; would only be good at one of either tree climbing or running Disruptive - favors both extremes, so the lizard would be good at BOTH tree climbing and running
Do you think that gene flow typically increases the genetic variation, decreases, genetic variation, or is equally likely to increase or decrease genetic variation in populations? Explain your reasoning.
The flow of individuals in and out of a population introduces new alleles and increases genetic variation within that population.
Explain how natural selection changes allele frequencies in populations. What determines which alleles are beneficial?
• Change in allele frequencies due to unequal survival and reproduction (unequal fitness) • Can lead to adaptations -adaptation: a heritable trait that increases an individual's relative fitness
Explain why it is important to consider both phenotype frequencies and allele frequencies when assessing microevolutionary change.
• Relationship between genotype and phenotype is complex -SAME phenotype frequencies can be due to DIFFERENT allele frequencies -DIFFERENT phenotype frequencies can result from the SAME allele frequencies -changes in phenotype distribution may NOT be due to changes in allele frequencies
