Freeman Biological Science - Chapter 26 Evolutionary Processes
Terms in this set (91)
What are four processes that can shift allele frequencies in populations?
natural selection, genetic drift, gene flow, mutation
What does natural selection do in a population?
It increases the frequency of certain alleles
What is the difference between genetic drift and gene flow?
Genetic drift - causes allele frequencies to change randomly, not selection of fitness
Gene flow - occurs when individuals leave one population, join another, and breed
What is the definition for a mutation?
A mutation modifies allele frequencies by continually introducing new alleles
What does a phylogenetic tree represent?
Shows the relationship between ancestral and derived species
There are four parts of a phylogenetic tree. What are they?
Root - how everything is related
Node - where there is a split
Branch - can tell about time
Tip - means there is no more splitting
Synapomorphy = ?
share derived character
What is an outgroup?
Usually the first taxa to split off and is distantly related to the rest of the taxa on the tree
What makes sister taxa different from just taxa?
Sister taxa are more closely related, while taxa are just levels/groups
In general terms, what does the Hardy-Weinberg Principle do?
tell us what to expect if selection,generic drift, gene flow, and mutation are not affecting a gene, and if mating is random with respect to that gene.
An approach where that all of the alleles from all the gametes produced in each generation go into a single group called the gene pool and then combine at random to form offspring.
i.e. Clam and starfish shooting gametes in the water.
If there is two alleles in a population (p and q), what is the formula for Allele frequencies:
If there is two alleles in a population (p and q), what is the formula for Genotype frequencies:
p^2 + 2pq + q^2 =1
Favored traits have a ______ _______?
Hardy-Wien only works for ___ gene with ___ alleles.
What five assumptions must be met for the Hardy-Weinberg Principle?
1) RANDOM MATING - picking gamete from gene pool at random
2) NO NATURAL SELECTION - all parental generations survived and contributed an equal number of gametes
3) NO GENETIC DRIFT - alleles picked in their exact frequencies
4) NO GENE FLOW - no new alleles added or lost
5) NO MUTATION - didn't consider other new alleles being added to gene pool
What does it mean when the observed matches Hardy-Wein?
that the population is not affected by any of the four evolutionary processes and that mating was random with respect to the gene
When discussing the HLA genes, what were the two explanations for why there may have been more heterozygotes than homozygotes?
1) Mating may not have been random with respect to the HLA genotype
2) Heterozygotes may have a higher level of fitness
What is the mating between relatives known as?
What are the two fundamental points about inbreeding?
1) increase in homozygosity, decreases heterozygosity
2) doesn't cause evolution because allele freq do not change in population as a whole
Does nonrandom mating change both genotype freq and allele freq?
No; it only changes genotype freq
What does inbreeding do to evolutionary change?
It speeds up evolutionary change but does NOT directly cause evolution. It increases the rate at which natural selection eliminates recessive deleterious alleles.
What is the decline in average fitness that takes place when homozygosity increases and heterozygosity decreases?
What are the four types of natural selection? Give a brief description of each.
1) Directional - average phenotype changes in one direction
2) Stabilizing - reduces both extremes in a population
3) Disruptive - opposite of stabilizing; eliminates phenotypes near the average and favors extreme phenotypes
4) Balancing - no single allele has a distinct advantage
What is genetic drift?
change in allele freq in a population due to chance
What are the three key points for genetic drift? Where does genetic drift impact the most?
1) it is random with respect to fitness
2) most pronounced in small populations
3) lead to random loss or fixation of alleles
most pronounced in small populations and has a BIG IMPACT
What are two examples of genetic drift that were mentioned in class?
1) founder effect = immigrants establish new population
2) genetic bottleneck = high mortality strikes at random
_______ is when individuals leave one population, join another, and breed. Movement of alleles between populations.
What is the most common outcome of gene flow?
it equalizes allele frequencies between the source population and the recipient population
Gene flow is random with respect to _________.
What would happen to evolution if there was no mutation?
Evolution would eventually stop because there would be no variation for selection and drift to act on.
What are the three different types of mutations?
1) Point mutations - a mutation affecting only one or very few nucleotides in a gene sequence. 1/100,000
2) Chromosome-level mutations - gene duplication which increases the number of copies of a gene; may lose function or create new alleles (add, delete)
3) lateral gene transfer - transfer of genes between species
Only ______ creates new alleles. This process is also slow compared to selection, genetic drift, and gene flow.
How did diversity come to be?
mutation, natural selection, *change in allele frequencies
How can we tell if allele frequency has changed within a population?
observe and measure, model- predicted expected genotypes from allele frequencies under NO evolution, null hypothesis, no evolution, allele frequency
What should happen.. if no evolution?
allele frequency would stay the same
What do genetic drift, gene flow, and mutation have in common?
What is a gene pool?
single group of alleles from gametes in each generation
What is the most extreme form of self breeding, extreme inbreeding?
What is a human example of inbreeding?
What are deleterious alleles?
alleles that lower fitness
What is genetic variation?
the number and relative frequencies of alleles that are present in a particular population, decreases genetic drift
Who does genetic drift have a big impact on?
What are the 4 modes? Explain.
~ directional selection: favors one extreme phenotype, causing average phenotype in pop to change in one direction, genetic variation is reduced
~ stabilizing selection: favors phenotypes near the middle of the range of phenotypic variation, maintaining average phenotype, genetic variation is reduced
~ disruptive selection: favors extreme phenotypes at both ends of range of phenotypic variation, genetic variation increases
~ balancing selection: no single phenotype is favored in all populations of a species at all times, genetic variation is maintained
What is an example of stabilizing selection?
When stabilizing selection acts on normally distributed traits, individuals with extreme phenotype experience poor reproductive success..
What is an example of disruptive selection?
finches- small and large fruits, so small birds ate small seeds, large birds ate large seeds, and intermediate birds struggled to eat either
What is an example of balancing selection?
Rare alleles responsible for coloration in guppies are favored because predators learn to recognize common color patterns this causes an a balancing of selection.
What is an example of directional selection?
When directional selection acts on traits that have a normal distribution, individuals at one end of the distribution experience poor reproductive success.
If genetic drift decreases, what happens to genetic variation within the population and between the population?
genetic drift decreases genetic variation within population and increase genetic differences between populations
Movement of alleles between populations tends to reduce their what?
(variation within population increases)
What is an example of lateral gene transfer?
~ resistance to antibiotics in bacteria
~ parasites cause malaria
What is an evolutionary process that increases genetic diversity in population?
As an evolutionary process, mutation is (slow, average, or fast) compared with selection, genetic drift, and gene flow.
What is the ultimate source of genetic variation?
Would evolution eventually stop if mutation didn't occur?
Can mutation alone change allele frequencies?
mutation alone is usually inconsequential in changing allele frequencies at a particular gene
Do allele frequencies change over time?
How should observed genotype frequencies and allele frequencies differ from those expected under Hardy-Weinberg principle when inbreeding is occurring?
the proportions of homozygotes should increase, and the proportions of heterozygotes should decrease, but allele frequencies will not change if no selection is occurring at this locus
How should observed genotype frequencies differ from Hardy-Weinberg proportions under directional selection?
there will be an excess of observed genotypes containing the favored allele compared to the proportion expected under Hardy-Weinberg proportions
Describe how drift could explain differences in a genotype frequencies among populations.
if allele frequencies are changing due to drift, the populations will behave like the simulated population, frequencies would drift up and down over time, and diverge
Explain why genetic drift leases to a random loss or fixation of alleles.
when allele frequencies fluctuate randomly up and down, sooner or later the frequency of an allele will hit 0. that allele is lost from the population, and the other allele is fixed
Explain why genetic drift is particularly important as an evolutionary force in small populations.
in small populations, sampling error is large
ex.) the accidental death of a few individuals would have a large impact on allele frequencies
Why does natural selection violate the Hardy-Weinberg principle?
the hardy-weinberg principle predicts that allele frequencies will stay the same over time. natural selection favors some allele over others causing the frequency of those alleles to increase
How could genetic drift be important to the management of endangered species?
genetic drift will rapidly reduce genetic variation in small populations. its a high priority to keep the populations of endangered animals as large as possible
How could gene flow be important to the management of endangered species?
in some cases, gene flow could be used to increase genetic variation and reduce inbreeding depression. however, gene flow can also be dentrimental if the new alleles reduce the fitness of the endangered species
Explain how mutation could be important to the management of endangered species.
mutation rates themselves are too slow to affect an endangered population in a short time- unless a deleterious or beneficial mutation exposes the population to selection
In what sense is the Hardy-Weinberg principle a null hypothesis?
It defines what genotype and allele frequencies should be expected if evolutionary processes and nonrandom mating are not occurring.
Why isn't breeding considered an evolutionary process?
it does not change allele frequencies
Why is genetic drift aptly named?
it causes allele frequency to drift up and down randomly
What does it mean when an allele reaches fixation?
it has a frequency of 1.0
T/F: Gene flow can either increase or decrease the average fitness of a population.
Mutation is the ultimate source of genetic viability. Why is this correct?
Mutation is the only source on new alleles.
How does gene flow impact genetic variation?
Decreases variation between populations
What is a null-hypothesis?
predicts there is no differences among the treatment groups in a experiment.
What is inbreeding and how is it related to nonrandom mating?
Inbreeding is mating within a closely related group, pick the mate, not random, increases homozygosity and decreases heterozygosity...but DOESN'T CHANGE allele frequencies, only a change in genotype frequency, BUT can speed up rate at which natural selection eliminates recessive deleterious alleles from a population
what happens to allele and genotype frequencies if inbreeding is occurring?
allele frequencies don't change
only a change in genotype frequency
Why do we say inbreeding is "bad"? (include inbreeding depression)
Inbreeding depression: because of the depressive alleles occurring more often when inbreeding occurs
How do the types of mutations impact genetic variation?
Restores/increases genetic diversity - creates NEW alleles
Point mutation: pretty slow, change in 1 nucleotide in DNA sequence
Chromosome level changes: addition/deletion; pieces of chromosome can insert, change, flip
Lateral gene transfer: between species, pieces of genome of 2 different species are exchanging or bombarding another species
natural selection Definition/ Description
Certain alleles are favored
Genetic drift Definition/ Description
Random changes in allele frequencies; most important in small populations
Gene flow Definition/ Description
Movement of alleles between populations; reduces differences between populations.
Mutation Definition/ Description
Production of new Alleles
Natural Selection Effect on Genetic Variation
Can maintain, increase, or reduce genetic variation
Genetic Drift Effect on Genetic Variation
Tends to reduce genetic variation via loss or fixation of alleles
Gene Flow Effect on Genetic Variation
May increase genetic variation by introducing new alleles; may decrease it by removing alleles.
Mutation Effect on Genetic Variation
Increases genetic variation by introducing new alleles
Natural selection Effect on average fitness
Can produce adaptation, increasing fitness
Genetic Drift Effect on average fitness
Random with respect to fitness; usually reduces average fitness
Genetic flow Drift Effect on average fitness
random respect to fitness; may increase or decrease average fitness by introducing high- or low- fitness allele
Mutation effect on average fitness
Random with respect to fitness; most mutations in coding sequences lower fitness.
What is sexual selection
type of natural selection that leads to the evolution of traits that helps individuals attract mates. It usually has a stronger effect on males than on females.
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