chapter 23: evolution of populations

what evolves?

what doesn’t evolve?

populations, individuals

why do individuals not evolve?

individuals acclimate to the environment. they don’t adapt because that’s microevolution. they don’t pass down the acclimation.

what is microevolution?

a change in allele frequencies in a population over generations, not resulting in a new species

what are the 3 widely accepted mechanisms that cause allele frequencies to change? (AKA that causes microevolution)

* which is most effective?

natural selection, genetic drift, gene flow. natural selection

these 3 mechanisms cause allele frequency change: natural selection, genetic drift, gene flow

* which of these cause adaptive evolution?

natural selection

what is the name for when darwin’s & mendel’s ideas were combined/reconciled? rather than looking at just changes, incorporated study of genetic changes were included

the modern synthesis (new synthesis)

what is modern synthesis (new synthesis)?

reconciled darwins (NS) & mendel’s (theories of inheritance) ideas

when was the idea of modern synthesis created?

1940s

what is the prerequisite for natural selection?

genetic variation

do clones have genetic variation?

no

what is the source of genetic variation?

mutations

what is genetic variation?

variation in the DNA sequence of genomes

what are the 2 things that genetic variation is measured as?

average heterozygosity & nucleotide variability

what is heterozygosity

has dominant & recessive alleles

genetic variation is measured by 2 things: average heterozygosity & nucleotide variability.

* define both

average heterozygosity measures the average percent of loci that are heterozygous in a population. nucleotide variability compares the DNA sequences of pairs of individuals

what does sexual reproduction do in regards to alleles?

it shuffles existing alleles into new combinations

______ of alleles is more important than mutation in producing the genetic differences

recombination

recombination of alleles is more important than mutation in producing genetic differences (AKA that cause genetic variation in sexual reproduction).

* what are 2 examples of allele recombination?

independent assortment & crossing over

describe independent assortment

alleles of different genes get sorted into gametes independently of one another

describe crossing over

When two chromosomes — 1 from mom and 1 from dad — line up, parts of the chromosome can be switched. the 2 chromosomes contain the same genes, but may have different forms of the genes

what does sexual reproduction allow for?

natural selection

does sexual or asexual reproduction produce clones?

asexual

does sexual or asexual reproduction have natural selection?

sexual

why does asexual reproduction not have natural selection?

because they’re all clones, they’re genes are all the same and there’s no genetic variation

what are some examples of asexually reproducing organisms?

plants, some microbes, sea anemone

is it harder to reproduce sexually or asexually? why? (AKA which has a reproductive handicap)

sexually, because it’s more costly/more of a process

if sexual reproduction is a handicap, why has it persisted?

it produces genetic variation that may aid in disease resistance

some phenotypic variation does NOT result from genetic differences among individuals.

* what is the main influence that does cause phenotypic variation in these situations?

environment (epigenetics)

only _____ variation can have evolutionary consequences

inherited

what’s an example of non-inheritable variation?

some caterpillars eat leaves & grow to look like leaves/stems. other caterpillars of the same species eat flowers & grow to look like flowers. their appearances aren’t heritable variations. their appearances are influenced by the food they ate/their environments

define mutation

any change in an organism’s dna

mutation has a ____ effect on ____ populations.

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example: it takes 2000 generations for mutation alone to change an allele frequency 1%

small, large

_____ has a small effect on large populations. BUT there are a lot of genes, so cumulative effects of mutations can be detected.

mutations

**IMPORTANT POINT:**

what provides raw material for natural selection to work on, so ultimate change can be great?

mutation

**IMPORTANT POINT:**

what does mutation provide for NS to work on, so that ultimate change can be great?

raw material

**IMPORTANT POINT:**

example: some rhinos have horns & some don’t. what role does mutation play? what role does NS play?

mutation determines if the rhino has a horn. NS allows the rhino’s horn to get bigger in subsequent generations

what are the 2 things that allow new genes & alleles to arise?

mutation & gene duplication

does mutation or natural selection cause adaptations?

* for the other term - what does it provide for adaptation to happen?

natural selection, a base

only mutations in cells that produce ____ can be passed to offspring

gametes

define point mutation

a change in one base in a gene

mutations in noncoding regions of DNA are harmless…

* always
* often
* rarely
* never

often

mutations in genes can be ____ because of redundancy in the genetic code

neutral

why can mutations in genes be neutral?

because of redundancy in the genetic code

during mutation:

change in protein production is harmful…

* always
* often
* rarely
* never

often

during mutation:

change in protein production is beneficial…

* always
* often
* rarely
* never

rarely

are mutation rates high or low in animals & plants?

low

define population

localized group of individuals of the same species

define gene pool

consists of all the alleles for all loci in a population

define fixed locus

all individuals in a population are homozygous for the same allele

if everyone was homozygous dominant, could natural selection cause the recessive allele to take over?

no

what is the main idea of the HW Theorem? (hardy weinberg theorem)

if the organisms are well-adapted to their environment, then they won’t change or evolve

does HW Theorem describe an evolving or non-evolving population?

non-evolving

HW Theorem:

* allele frequencies & genotype frequencies stay constant from one generation to the next unless… ?

there are non-random effects (evolution)

* what is the equation for allele frequency?
* what is the equation for genotype frequencies?

p+q=1, p^2+2pq+q^2=1

describe the harm in inbreeding

the parents are likely both carriers of certain diseases or tendencies. it is more likely that their offspring is homozygous recessive for those diseases.

HW Equilibrium:

* gene frequencies remain the same throughout generations -- AKA no _____

evolution

**IMPORTANT POINT:**

what are the 5 conditions for HW Equilibrium that are rarely met in nature? (if these things are in place, nothing will evolve)

extremely large population size, no gene flow, no mutations, random mating, no natural selection

these are the 5 conditions for HW Equilibrium that are rarely met in nature? (if these things are in place, nothing will evolve)


1. extremely large population size
2. no gene flow
3. almost no mutations
4. random mating
5. no natural selection

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* what is an example of gene flow?
* what is random mating?
* why is it likely that “random mating” would NOT be reached?

migration, no selection, because animals are choosy and selective about their partners

if all of the factors for HW Equilibrium are met, will evolution occur?

no

what are the 8 mechanisms that could cause evolutionary changes? (AKA Hypothesized Evolutionary Mechanisms)

* these prove that Darwinian NS isn’t the only theory

natural selection, genetic drift, gene flow, species selection, self organization, neutral theory, natural genetic engineering, intelligent design

natural selection:

* differential ____ success (some live, some don’t)
* this is the only method that causes ____
* accumulates & maintains favorable _____

reproductive, adaptation, genotypes

what is phenotypic polymorphism?

describes a population in which 2+ distinct morphs for a character are each represented in high enough frequencies to be readily noticeable

what does phenotypic polymorphism prove?

environment affects appearance

what is genetic polymorphism?

heritable components of characters that occur along a continuum in a population

_____ conditions make it difficult to determine what traits are inherited & what isn’t

environmental

an example of genetic polymorphism is the yarrow plant. it’s seeds were taken from a mountain range at a variety of altitudes & placed in a level field. they grew at different heights. the flowers grew at different heights on the level field. was this genetic or environmental? why?

genetic because the seeds were moved

define a cline

change in organism by geography

what are the 2 factors of individual fitness?

survival & reproduction

define individual fitness

the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

is having 9 kids an example of high individual fitness or low individual fitness?

high

define relative fitness

contribution of a genotype to the next generation as compared to the contributions of alternative genotypes for the same locus

is it high or low relative fitness if the genotype shows up more in the next generation?

high

natural selection increases the frequencies of alleles that enhance survival & reproduction. therefore, the adaptive match between an organism & it’s environment _____

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* increase or decrease?

increase

define niche

role an organism plays (ex: predator vs prey)

what are 5 types of natural selection?

directional selection, diversifying selection, stabilizing selection, sexual selection, frequency dependent selection

define stabilizing selection

loses extreme phenotypes

define directional selection

favors one phenotype extreme over the other, causing the mean to shift

define diversifying selection

intermediate phenotype disfavored, causing phenotype divergence (2 extreme phenotypes left)

sexual selection is based on _____ ____

sexual dimorphism

sexual selection is based on sexual dimorphism. define this term

distinct secondary characteristic differences between males & females

sexual selection is a type of _____ mating

nonrandom

sexual selection is a type of nonrandom mating. what are 3 types of nonrandom mating? define each

inbreeding (close relatives), selfing (asexual reproduction), assortative mating (females prefer to mate with males with certain phenotypes)

what may be the cause of inbreeding? why is it bad?

geographic location or lack of other opportunities. elevates frequency of homozygous recessive/decreases diversity

sexual selection emphasizes mating over ____

survival

what is the good genes hypothesis?

if a trait is related to male health, females use the selected feature to evaluate overall health & superior genes of the male

what are 3 types of sexual selection?

intrasexual, intersexual selection, male showiness

define intrasexual selection

competition among individuals of one sex for mates of the opposite sex

define intersexual selection (AKA mate choice)

occurs when individuals of one sex are choosy in selecting their mates

define male showiness

due to mate choice. increases a male’s chances of attracting a female, while decreasing his chances of survival

why are females often more picky about who they mate with than males?

because they invest more energy into childbirth & childrearing than the males

describe the significance of this picture

male frogs call to attract females. but bats hear the calls and go to eat the male frog. the benefit is that the female frogs like the male frog’s call. the more the male frog calls, though, the more likely it is to get eaten by the bat. over generations, if the females started being picky about features of the male frog over their call, then bats would have less food since frogs would stop calling

what is frequency-dependent selection?

the fitness of a phenotype declines if it becomes too common in the population. selection favors whichever phenotype is less common in a population

describe the significance of this picture and what it leads to

if there are more left-mouthed than right-mouthed fish in an area: the more often the big fish is attacked on the left side (with left-mouthed fish), the better the big fish gets at dodging the left-mouthed fish. this leaves left-mouthed fish without food, so they’ll die out. right-mouthed fish (previously in the minority) become more popular

what does balancing selection lead to?

a state called balanced polymorphism - AKA heterozygous advatage

define heterozygote advantage

some individuals who are heterozygous at a particular locus have greater fitness than homozygotes

what’s an example of heterozygote advantage? give a thorough description

sickle cell anemia & malaria resistance. if someone is homozygous recessive for sickle cell, it’s often lethal. if someone is homozygous dominant, less of their kids will have sickle cell, and fewer will die of malaria. if someone is heterozygous, they’ll be a carrier of sickle cell & have resistance to malaria. if malaria increases, sickle cell decreases. because with malaria, all die. & with sickle cell, some kids might die if marrying a carrier

does natural selection work on neutral variation?

no

what are some examples of natural selection?

darwin’s finshes, soapberry bugs, antibiotic resistance

describe how natural selection worked for the cane toad & its selection for longer legs.

introduced to australia to eat bugs. for the first 20 years, they spread at 6 miles/year. they now spread at average 30 miles/year. allows them to secure the best habitat at the new terrain. migration = no competition with other toads because none are there yet

give a short example of how butterflies experienced natural selection

evolved resistance to a killer bacteria in one year