Miami University 206W exam2
Describe how selection based on food availability (population density) can influence the prevalence of yeast cells with parasitic mitochondria. What makes a mitochondrion parasitic? What was the control for the experiment and what did it control for?
"parasitic" mitochondria (missing genes for enzymes that carry out respiration) live off the yeast and offer nothing in return (also reproduce more quickly than normal mitochondria) As a control, the researchers established yeast cultures in which the founding individuals contained both chloramphenicol-susceptible and chloramphenicol-resistant mitochondria Small populations have less competition among yeast cells so there is not strong selection against predominantly parasitic mitochondria-containing yeast compared to high density populations Large (high density) populations have more competition and therefore selection should work against yeast cells with a lot of parasitic mitochondria
Why is linkage disequilibrium potentially important and how can linkage disequilibrium be maintained in populations?
-A deleterious allele might be maintained in a population if it's in linkage disequilibrium with an advantageous allele -Alleles at two loci in linkage disequilibrium may be an adaptive combination -One might think selection is acting on an allele at one locus, but the frequency of that allele may actually be affected by selection on an allele of a linked gene
Explain the costs that may be associated with sexual reproduction compared to asexual reproduction.
-Cost of producing males/meiosis -Searching for partners is costly in terms of time, energy, and risk (e.g., predation) -Exposure to diseases (i.e., STDs) and parasites
Explain narrow-sense heritability and distinguish it from broad-sense heritability.
-The degree of "genetic determination" of a trait; Broad-sense heritability (H2) = VG ÷ VP -The extent to which quantitative traits are inherited by offspring from their parents = narrow-sense heritability (h2)
Explain the various ways in which loci can be maintained in a polymorphic state?
1) Alleles for a polymorphic locus are functionally equivalent (neutral theory) 2) Mutation-selection balance 3) Heterozygote superiority 4) Selection for/against different alleles at different times, places, ecological circumstances, and in males vs. females 5) frequency-dependent selection
What is the hypothesis for why there is greater genetic differentiation across geographic distances for Y chromosome loci compared to either autosomal or mitochondrial loci in humans. In other words, what may be causing the apparently higher rates of gene flow for autosomal and mitochondrial loci compared to those on the Y chromosome?
All people acquire autosomal and mitochondrial, only people with a Y chromosome get that loci. Thats why genetic drift is different, because they have different
What is the evidence that phenotypic plasticity in the phototaxic response of Daphnia has evolved in response to the densities of fish in lakes?
Another way to say that an individual's phenotype is influenced by its environment is to say that its phenotype is plastic Daphnia reproduces asexually most of the time. This makes them ideal for studies of phenotypic plasticity, because researchers can grow genetically identical individuals in different environments and compare their phenotypes. The average genotype in Lake Blankaart shows considerably more phenotypic plasticity than the average genotype in either of the other lakes. Blankaart is the only one of the lakes with a sizable population of fish. Fish are visual predators, and they eat Daphnia. A reasonable interpretation is that predation by fish selects in favor of Daphnia that avoids well-lit areas when fish are present.
Describe the potential effects of inbreeding depression. Why do we think inbreeding depression has such effects? Be able to explain how to calculate F for a particular set of relatives.
As inbreeding coefficient increases the number of offspring who don't survive
Explain Muller's ratchet and why it can result in "genetic load". What can reduce the genetic load in a population?
Asexual lineages are apt to be small and accumulate deleterious mutations Individuals with zero mutations can be lost by drift Then those with one deleterious mutation will be lost by drift, etc. Sexual reproduction
What does Maynard Smith's model indicate is the primary advantage of asexual reproduction? In relation to his model, why might sexual reproduction be so prevalent in nature despite the apparent advantage of asexual reproduction?
Asexual reproduction results in more offspring. The probabiliity for offspring surviving is higher for sexual reproduction
Explain why data for Pacific field crickets (fig. 7.12) illustrate an example of genetic drift.
Because the crickets came from New Gineia and Austrailia, they had to have traveled on boat so each island the boat arrived to would get a small population on crickets. This means that each population of crickets is different
For a locus that has only two alleles, describe how the selection is expected to act on a recessive allele that is lethal in the homozygous state and what the equilibrium frequency of that allele will be (all else equal) if the frequency of both alleles (the other one is non-lethal) is 0.5 at the outset of the experiment. Why does the frequency of the recessive allele stabilize at that frequency?
Because there are only 2 alleles and the one is lethal, it wouldn't be possible to show up at a full 1, only at .5
Describe the experiment in which a strain of C. elegans was either exposed to heat-killed pathogenic bacteria, pathogenic bacteria that had not yet infected C. elegans, or pathogenic bacteria taken from C. elegans that had died from the bacterial infection. How and why did the levels of outcrossing (i.e., sexual reproduction vary among the three treatments?
Control - exposed to heat-killed pathogenic bacteria; was always around .2, ended low Evolution - exposed to pathogenic bacteria from a stock population; outcrossing rate grew at first then fell Co-evolution - exposed to pathogenic bacteria selected for their ability to infect C. elegans; ended with highest outcrossing rate
Why are Controls used in experiments? What is the purpose of replicates? Why are subjects randomized in experiments?
Controls provide more data and help us determine if the experiment is acurite Replicates help us determine if the results we got are accurate or just chance Subjects are randomized so we get the best variety of subjects
Describe and distinguish among directional, stabilizing, and disruptive selection. Be able to give an example of each type of selection
Directional selection favors one side of the phenotype Stabilizing selection favors the middle of the phenotype Disruptive selection doesn't favor a phenotype or favors both sides
If a population is in HWE for a particular locus, what two features of the population for that locus must remain unchanged?
Frequency of alleles and genotypes
Describe the evidence for whether garter snakes behaviorally thermoregulate or Not.
Garter snakes in the wild are found under medium and thick rocks, not thin rocks, indicating they do thermoregulate
Describe the apparent trade-offs in the formation of red coloration in the Fuschia. What are the hypotheses for why the flowers turn red? What is the evidence that does or does not support the hypotheses?
Hypothesis 1: The more closely female flowers mimic typical male flowers, the more often they will trick bees into visiting. Selection on female flowers is stabilizing, and the best phenotype for females is identical to the mean phenotype of males Hypothesis 2: The more closely female flowers mimic the most rewarding male flowers, the more often they will succeed in duping bees. If larger male flowers offer bigger rewards, then selection on female flowers is directional, and bigger flowers are always favored over smaller flowers The larger the flower, the more bee approaches and visits it attracted. Selection by bees on female flowers is strongly directional.
Explain the different ways that heritability in the narrow sense can be measured/estimated. Explain the process by which investigators used tail length of mated pairs of mice and their offspring to estimate narrow-sense heritability of tail length.
Identical twins vs fraternal twins, what traits do they have in common, environment vs genetical traits Examine tail lengths of pairs of mice, measure their babies tail length Mice chart has line of best fit that is slope of heritability
Define genetic drift and describe under what circumstances it has its greatest effect on frequencies of alleles and why that is the case. If only genetic drift is affecting a locus, what will eventually happen to the frequency of each allele if there are just two alleles for the locus?
If there are 2 alleles then the frequency of each will slowly drift to .5
What would you predict would happen to the distribution of the banding phenotypes if suddenly there were only gene flow (and no selection or other evolutionary "forces") influencing those populations? In other words, how would you expect the histograms in Fig 7.6 to change under those circumstances?
If there was only gene flow there wouldnt be any other force at play so the allele frequencies will stay the same through the generations.
What does it mean that two genes are linked (for the purposes of this course)?
If they are on the same chromosome
Compare the frequencies of the two alleles above to what they would be if selection actually favored heterozygotes for the locus.
If they favored the heterozygote, then the frequency would go to .5 instead of 1 or 0
Explain John Maynard Smith's model for the relative reproductive success of individuals reproducing sexually and asexually. What assumptions are made in his model?
John Maynard Smith proposed "null" model that assumed a female's reproductive mode (sexual or asexual) did not affect 1) the number of offspring she produces, or 2) the probability that her offspring will survive
Define linkage equilibrium and linkage disequilibrium. Make sure your answer refers to the frequencies of alleles of two linked loci. What is the evidence that any two loci are in a state of linkage disequilibrium?
Linkage equilibrium - frequencies of alleles at one locus are independent of frequencies of alleles at another locus (on same chromosome) same frequency Linkage disequilibrium - frequencies of alleles at one locus are dependent of frequencies of alleles at another locus (on same chromosome) different frequency
Why doesn't natural selection just result in the one best-adapted suite of traits? In other words, describe all the ways in which genetic variation for fitness is maintained in populations.
Most pops. not in equilibrium for directional/stabilizing selection Steady and slow supply of mutations, some beneficial Balance (equilibrium) between selection and deleterious mutations If selection on them weak, and they have a small additive influence on quantitative traits, substantial genetic variation may persist Disruptive, frequency-dependent, and variable selection may be more common than generally recognized
What are the five evolutionary "forces" that would cause a particular locus to not be in HWE equilibrium?
Natural selection, mutation, gene flow, genetic drift, nonrandom mating
Define Effective Population Size. What factors make it less than N and why do they tend to do so?
Ne is the actual number of reproducing adults • Number of years to reproductive age • Average age in the population • Sex ratio of individuals that reproduce • Non-random mating, or • Any factor that reduces genetic contribution of some individuals to future generations
Describe the relationship between infection with HIV and the 32 CCR5 allele.
People who have 32/32 survive AIDS but 32/+ and +/+ dont
Distinguish between qualitative and quantitative traits and give an example of each. How do the two categories of traits differ with regard to their genetic basis?
Qualitative traits are categorical (one/a few loci cause one phenotype or another - e.g., elderflower orchid flower color) Quantitative traits have continuously distributed phenotypes (additive effects of different combinations of alleles at multiple loci)
How can alleles at loci that are in linkage disequilibrium become in linkage equilibrium?
Sex, specifically recombination
Describe the experiment in which investigators created populations of 8 randomly chosen females and 8 randomly chosen males to establish a new population for 107 experimental populations over the course of 19 generations. What happened to the frequency of the allele they were measuring over the course of time (i.e., generations) and why did it change?
Some generations had an increase in frequency and some had a decrease. At the end of the experiment 30 generations lost the allele so frequency is 0 and 28 generations a=had a frequency of 1, vey close to the 1:1 ration you would predict with genetic drift
Describe how selection on multiple traits (e.g., beak depth and width in ground finches or striped/spotted markings and types of locomotion patterns in snakes) can result in varying selection "planes."
Sometimes selection works with multiple traits, like with beak sizes and widths, selection planes can show us the different traits and how they connect
Define gene flow (remember "migration" (as used in the text) = dispersal) and explain how selection and gene flow may account for the distribution of water snake genotypes for different banding phenotypes on the Ohio mainland and the islands in Lake Erie (i.e. be able to explain Fig. 7.6).
The alleles flow through the generations and migrate with the snakes as they move places and reproduce
Explain frequency-dependent selection and be able to explain the experimental results shown in Fig. 6.24.
The amount of a certain allele will impact if it gets selected or not, in random selection it has less of a chance of getting chosen
If only mutation is affecting the frequency of an allele at a particular locus, what sort of evolutionary outcome do you expect over many generations?
You would expect a small difference in the frequency of that allele
Population
a group of breeding individuals and their offspring
Gene pool
all alleles in a population
Describe the factors we think caused the steep decline in Florida Panther populations even after they had been protected by the Endangered Species Act. What solutions can be used to help populations such as the Florida Panther?
The florida panther populations almost died off, then the protection act caused the panther to be able to reproduce, because the populations were so low the inbreeding coefficient spiked and caused the panther offspring to suffer
What is the relationship between a change in the proportion of heterozygotes and population size (i.e., be able to explain the formula Hg + 1 = Hg [1-(1/2N)])? In the experiment described in question 6) above what was paradoxical about the decline in heterozygosity? What are possible explanations for the paradox?
The frequency of heterozygotes indeed tends to fall, rapidly in small populations and slowly in large populations. Eventually one allele or the other will become fixed in every population, and the average frequency of heterozygotes will fall to 0. Because heterozygotes fall to zero, .5 wont happen as a final allele frequency, only 1 and 0
Describe the hypotheses, experiments, and evidence for why tephritid flies have markings on their wings and "wave" them. What did the control treatments control for?
The hypothesis is that they wave their wings to look like jumping spiders They cut the flies' wings off and replaced them with wings from other flies then observed what happened to them Greene's experiment supports the hypothesis that tephritid flies mimic their own jumping-spider predators to avoid being eaten
Describe the experiment in which C. elegans were exposed to selection (had to cross over rough surface to get to food). How did the three strains in both Control (not mutagenized) and Experimental (mutagenized) groups differ? What was the relationship between frequency of "outbreeding" and fitness (i.e., reproductive success) relative to the ancestral population from which the three strains were derived? How do the results relate to Maynard' Smith's model (ques. 6)?
There was asexual reproduction, wild type, and sexually. The sexual reproduction made the worm better at crossing the surface than the ancestrial group. Sexual group also had higher change in fitness. Results relate because the offspring survive better for the sexual group than the asexual group, reject assumption
How would you respond if someone asked you if a trait was genetic or environmental? What would be a better way to frame the question?
Traits are influenced by both genetics and environmental factors How much of the variation in a trait is due to variation in the genetic make-up of individuals and how much is due to variation in environmental effects on individuals?
If a population is subjected to natural selection, does it necessarily cause a change in the frequency of alleles and genotypes?
Yes, its not in HWE
What is the evidence (based on transgenic strains of E. coli as well as epidemiological data) for why the frequency of the ∆F508 allele of the cystic fibrosis transmembrane conductance regulator locus may be maintained at a rate higher than what a mutation/selection balance would yield (i.e., explain the data in Figs 6.31 a) and b) with regard to typhoid fever, caused by Salmonella typhii.
homozygous F508 cells were almost totally resistant to infiltration by S. typhi, while homozygous wild-type cells were highly vulnerable. Heterozygous cells were partially resistant; they accumulated 86% fewer bacteria than did the wild-type cells
What is one hypothesis for why males in bat species that live in larger social groups have larger testes? What does one have to consider when comparing data from many closely related species?
large testes are an adaptation for sperm competition The species has very similar genetics so they are predisposed to have similar data
Explain the Hardy-Weinberg Equilibrium (HWE) model
p^2+2pq+q^2=random mating yield
What is the coefficient of inbreeding (F)? What is the relationship between heterozygosity of an inbred population and that in a random mating population (i.e., be able to explain the formula HF = HO(1 - F))?
probability that the two alleles (at a locus) in an individual are identical by descent
Describe the "Red Queen" hypothesis and discuss mode of reproduction (sexual versus asexual) of snails in New Zealand and their rates of parasitism by trematodes. What are possible explanations for the higher rate of sexual reproduction (i.e., proportion males) in populations with higher rates of trematode infections?
sex is adaptive during perpetual arms races between biological antagonists, selection is always going back and forth and evolution never stops
What are the hypotheses for why oxpeckers spend time with forest buffaloes. What does the evidence suggest? What does the evidence indicate about casual observations and explanations about adaptations?
the oxpeckers devoted more than 85% of their feeding time to three activities: licking blood from open wounds; probing their hosts' ears, apparently for wax; and scissoring their beaks through their hosts' hair, apparently gleaning and eating dead skin. The buffaloes don't like them doing this and try to get them away every few minutes