Bios 3300 Exam 2 Study Guide

who was the co-discoverer of natural selection (along with Darwin)?

Alfred Russel Wallace

what is artificial selection?

an evolutionary process in which humans consciously select for or against particular features in organisms

why was Darwin interested in pigeons?

Darwin realized that pigeon breeders acted like nature in the way they chose what traits to pass on based on the particular pigeons they mated

what do we mean by "artificial"? (artificial selection)

controlled/maintained by humans

what are the three steps to natural selection?

1. individuals vary in phenotype

2. some of this phenotypic variation is heritable

3. the variable, heritable traits affect an individual’s reproductive success

why is natural selection “natural?”

the traits are selected by nature, rather than humans/other force

struggle for existence

not all individuals reproduce, or reproduce maximally

why is Darwin's "struggle for existence" important for natural selection?

it determines which individuals are able to pass their genes down, and therefore influences the next generation

what is the consequence of natural selection?

evolution by natural selection - the genetic composition of the population will change across generations

if a population exhibits variation in a character, can natural selection act on that character?

yes, if that character increases mean population fitness

if the variation character is not variable due to heritable genetic factors, can it evolve by way of natural selection?

natural selection can operate on characters that are not heritable, but the population will not change its genetic composition across generations

does natural selection operate directly on phenotypes or genes?

phenotypes; genotypes change across generations as the alleles that contributed to the specific phenotype are more/less frequently passed down

why is it that to understand natural selection, one must think in terms of probabilities?

traits under natural selection only impact the probability of survival and reproduction

is natural selection testable?

yes

why is Peter & Rosemary Grant's work on Darwin’s finches an excellent example of evolution by natural selection? what trait evolved?

the trait had variation, it was heritable, the different seed sizes in each drought caused a struggle for existence; could keep track of all finches on island, so it was easy to observe/measure phenotype changes

beak depth increased after the first drought (when larger seeds were more available) and decreased after the second drought (when smaller seeds were more available)

what evidence was used to show that beak depth is heritable?

parent-offspring regression

what evolves: individuals or populations?

populations

what is a histogram?

graphical display that shows distribution of continuous, quantitative values

in 1977, a drought resulted in selection for deeper beaks. in 2004, a drought resulted in selection for narrower beaks, due to the presence of another species that was not there in 1977. what does this say about the nature of natural selection?

natural selection cannot predict the future, so deeper beaks reflect the impact that natural selection had on the previous generation

what does it mean to say the natural selection is non-random (systematic, in fact), but not necessarily progressive?

natural selection is not progressive; it can only filter variation according to fitness in the current population

what is wrong with this: fishes wanted to get onto land, so they evolved limbs?

evolution does not have an ultimate goal and animals cannot choose to evolve a new trait; new traits evolve over generations due to genetic variation

what is teleology?

doctrine of final causes; natural and historical processes are determined by their ultimate purpose

pick either A or B: populations reflect (A) the impacts of natural selection in the previous generation, or (B) the needs of the population in the next generation

A

using the tinkerer analogy, explain why it is that natural selection may not always lead to perfection?

tinkering proceeds step-by-step, which imposes limitations/evolutionary constraints on evolutionary change; evolution can only select on variation that already exists

compare and contrast local vs. global optima

global (best overall) and local (best locally) both exist, but cannot move between them if it requires a decrease of mean population fitness

if natural selection acts on phenotypes in a population, but the frequency of alleles in the next generation has not been altered, has evolution occurred? why might this happen?

no, if the characters were not heritable or the phenotype variation was caused by the environment

what is wrong with this statement: “the female decided not to breed last year, because resources were scarce and it would have been bad for the species.”

natural selection never favors a trait “for the good of the species,” it can only act on individuals and proceed without knowledge of the future

why is Hardy-Weinberg equilibrium important? what does it tell us about allele frequencies in a population?

provides a null hypothesis about how allele frequencies are expected to behave outside of any evolutionary processes

in the absence of evolution, allele frequencies will not change from generation to generation

what is the HW equation?

p² + 2pq + q² = 1

what are the frequencies of different genotypes represented by in the HW equation?

p² (AA), 2pq (Aa), q² (aa)

what are the 4 assumptions of HW equilibrium that, if violated, result in evolutionary change?

infinite population size, no migration (gene flow), no mutation, no natural selection

which assumption of HW, when violated, changes the frequency of genotypes, but does not directly change the frequencies of alleles?

random mating

how many generations of random mating are required to re-establish HW equilibrium?

1

if a population is in HW equilibrium, and all the assumptions are met, will the frequencies of alleles shift between generations?

no, will remain the same

what is a significant critical value with 1 degree of freedom?

3.841

what is a critical value? (abstract terms)

threshold value for determining whether or not something is statistically significant

describe “statistically significant” in words

random chance has a low probability of generating the data collected

what P value is typically taken as “significant”?

<= 0.05

in words, what is a P value?

probability of obtaining test results at least as extreme as the result actually observed, assuming the null hypothesis is correct

absolute fitness

the fitness of a phenotype is the average lifetime reproductive success of individuals with that phenotype

how do you calculate absolute fitness?

abs. fitness = (# observed at time t₁)/(# expected at time t₁)

relative fitness

the fitness of a phenotype compared with others in the population

how do you calculate relative fitness?

divide all absolute fitness values by the maximum absoulte fitness

what are fitness componets?

an individual’s score on a measure of performance expected to correlate strongly with the genetic contribution to the next generation

is fitness a description or an explanation?

description

can the causes of differences in fitness be studied?

yes

what is the relationship between ecology and fitness?

the phenotype of an organism in relation to the environment it inhabits determines how fit that organism is

can natural selection act on a mutation that is not expressed in the phenotype?

no

for natural selection to act on it, the mutation would have to be linked to another gene that shows a phenotype natural selection can act on (indirect selection)

true/false: mutation is random with respect to future needs.

true

true/false: the environment induces adaptive mutations

false

what is a tautology? why is fitness not a tautology?

“circular logic” (survival of the fittest); fitness is not an explanation

what are the 3 parts of the general selection model?

genetic variance, mean population fitness, average effect of an allele substitution

pq (general selection model)

genetic variance; the larger the pq, the greater the rate of evolution

W (general selection model)

mean population fitness; lower W = faster rates of evolution, higher W = slower rates of evolution

q(W₃ - W₂) + p(W₂ - W₁) (general selection model)

average effect of an allele substitution; interaction between relative fitness and allele frequency, larger differences in relative finesses cause a greater rate of evolution

how does natural selection impact mean population fitness?

can only increase it

what is directional selection?

a mode of natural selection in which a phenotype is consistently favored; which causes the mean value of that trait to change, but not the variation

selection with dominance

the fitness of the homozygote dominant and heterozygote will be the same

selection with dominance, when the fitness of the homozygote recessive is 0

the recessive allele frequency will decrease rapidly at first when it is common, but very slowly when it is rare

what is eugenics?

the study and practice of control over the evolution of human populations in an effort to decrease the frequency of undesirable traits

from a strictly population genetic standpoint (setting aside for a moment the horrors of implementation), why is it that eugenics would not work?

due to the mutation-selection balance, and when trying to decrease the frequency of an already rare recessive mutation to be even rarer, it would take a larger amount of generations and time