Midterm 2
A SNP for a particular gene "A" results in two different alleles that exist in a pop of Tasmanian Devils numbering 500. Suppose you sequence the genome of each individual in the population and find that 750 of the sequence you obtain have a "C" at a particular position in Gene "A" and 250 of the sequences have a "T" at the same position. Calculate the allele frequencies of these two alleles.
-500 tasmanian devils with two alleles each= 1000 alleles -750--> C 250--> T -C allele frequency 750/ 1000= .75 -T allele frequency 250/1000= .25
The speed gene has two common alleles, distinguished by a single amino acid diff that changes the charge of the protein. F allele is in fast rabbits and S allele is in slower. 4 individuals are FS hetero, 2 are F homo, and 1 is S homo. Determine the allele freq for the speed gene based on the gell above and the given labels
-FS--> 4 (8 alleles) -FF--> 3 (6 alleles) -SS--> 1 (2 alleles) -total number of alleles= 16 -F gene frequency: 6+4 (half of FS)= 10/16= .625 -S frequency: -2+4= 6/16= .375
Foxes pray on the slowest rabbits and eliminates most of them, causing a decrease in the allele frequency in the S allele, what is the EVOLUTIONARY DRIVING FORCE behind this? What TYPE OF SELECTION is being served under this driving force, graph.
-Natural selection -Directional selection
what are some ways you can determine how old a species/ organism is?
-molecular clock--> measure evolutionary divergence depending on genetic mutation -relative fossil dates--> record of species, where fossil is embedded -radiometirc dating--> using proportion of radioactive isotopes present
what are the 5 conditions that hardy weinberg assumes?
-random mating -large pop (dec genetic drift) -stable allele freq (no mutations) -no natural selection (every individual has equal chance of survival -no immigration or emigration (isolation)
You notice a population of 100 flowering plants that all look identical (phenotypic clones), spanning an area of 100 square meters (m2). You collect samples from every individual, sequence their DNA and determine that they are diploid and also genetic clones. -You return to the population after a year, sample the population again and discover a mutation in one individual. calc the freq of this new allele
.005
Imagine the following genotype frequencies in a population: p2 = 0.49, 2pq = 0.42, q2 = 0.09. Now assume that there is nonrandom mating where individuals with one genotype will only mate with individuals that also have their genotype. Assume this pattern of mating goes on until the frequency of heterozygotes is effectively zero. What will the frequency of allele p be in the population?
0.7
BB=16 Bb=222 bb=762 what is the freq of B
1. B=32 B=222 b=222 b=1524 254/2000=.127
What are four ways you can determine what constitutes "a species"?
1. Biological species concept--> must produce viable fertile offspring. species are groups of interbreeding natural pop that are reproductively isolated from other such groups 2. Morpho species concept--> members of same species often look alike, but not always true. sexual dimorphism/cryptic species 3. Ecological species concept--> members of species are characterized by niches; on species per niche 4. Evolutionary/phylogenetic concept--> members of the same species share a common ancestor
The gene for the type of elbow joint is inherited in a dominant-recessive manner with the double jointed elbow being "E" and the normal elbow being "e". There are 300 chimps in a pop of which 50% are "EE", 25% are "Ee", and 25% are "ee". What are the allele frequencies in this population of chimps for the elbow joint gene?
1. EE--> .5 Ee--> .25 ee--> .25 2. each chimp has 2 alleles 3. total number of alleles= 300+300=600 4. "E" gene frequency .5 x 600= 300 .125 (half of "Ee") x 600= 75 300+75=375/600= .625 ----------------------------------- "e" gene frequency .25 x 600= 150 .125 x 600= 75 150+75= 225/600= .375
What are the 5 prezygotic factors
1. Habitat (spatial) isolation --> geographic (different locations); ecological (diff niches) 2. Temporal location--> diff fertility and breeding season 3. Behavioral isolation--> mating dances and calls 4. Gametic isolation--> biochemical; incomplete gametes, egg will not fuse with sperm
List fours ways in which evolution can occur
1. Mutation 2. Genetic Drift 3. Migration 4. Natural selection
The three conditions that must be satisfied for evolution by natural selection to occur are:
1. Variation 2. Heritability 3. Differential reproductive success based on that variation
what are two ways allopatric speciation can occur
1. dispersal --> move then barriers form 2. vicariance--> natural disturbance that creates a barrier
If 9% of an African pop in H-W equilibrium is born with the severe form of sickle cell anemia (SS), what percentage of the pop will be more resistant to malaria because they are heterozygous (SA) for the sickle cell gene?
1. f(SS)= p^2= .09 p=sqrt(.09) = .3 2. p+q=1 --> .3+q=1 q=.7 3. f(SA)= 2pq= 2(.3)(.7) = .42 42%
explain why a maladaptive allele might be kept in a gene pool
1. heterozygote advantage 2. masking (epistasis) -natural selection can keep deleterious alleles if they are recessive in heterozygotes and dont show up in phenotype or if they confer some advantage (sickle cell anemia)
What are the two post-zygotic factors
1. offspring not viable 2. offspring sterile
you sample 1000 individuals form a large pop for the MN blood group (blood type, genotype, number of individuals, resulting frequency) -M, MM, 490, .49 -MN, MN, 420, .42 -N, NN, 90, .09 find the freq of each allele in pop. the prob of offspring genotypes from each potential cross (MMxMM, MMxMN, MMxNN, MNxNN, MNxMN, NNxNN)
1. p^2=.49 --> p=sqrt(.49)=.7 q= 1-.7= .3 2. MMxMM--> 100% MM NNxNN--> 100% NN MMxNN--> 100% MN MMxMN--> 50% MM and 50% MN MNxMn--> 25% MM, 50% MN, 25% NN MNxNN--> 50% MN, 50% NN
Imagine the following genotype frequencies in a population: p2 = 0.49, 2pq = 0.42, q2 = 0.09. Now assume that there is nonrandom mating where individuals with one genotype will only mate with individuals that also have their genotype. Assume this pattern of mating goes on until the frequency of heterozygotes is effectively zero. In addition, there is also inbreeding depression such that individuals with the genotype represented by p2 die before they can reproduce. What will be the frequency of allele q?
1.0
suppose f(A)=.7 and f(a)=.3 what is the freq of heterozygotes in the pop
2(.7)(.3)=.42
In a given pop only the A and B alleles are present in the ABO system. A and B are codominant meaning AA, AB, BB express their own phenotype. If 200 ppl have type A blood, 75 have AB and 25 have B, what are the allele frequencies in this pop. Is pop in H-W eq
200--> A 75--> AB 25--> B Part 1: 1. count alleles: 200 AA--> 400 alleles (A) 75 AB--> 75 alleles A, 75 alleles B 25 BB--> 50 alleles B =600 alleles 2. calc allele freq: f(A)= 400+75/600= .79=p f(B)= 75+50/600= .21= q Part 2: HW? expected genotypes f(AA)--> .79^2= .62 f(AB)--> 2(.79)(.21)= .33 f(BB)--> .21^2= .04 observed genotypes f(AA)--> 200/300= .67 f(AB)--> 75/300= .25 f(BB)--> 25/300= .03 Not in HW eq
In a population of Mendel's garden peas, the frequency of the dominant A (yellow flower) allele is 80%. Let p represent the frequency of the A allele and q represent the frequency of the a allele. Assuming that the population is in Hardy-Weinberg equilibrium, what are the genotype frequencies?
64% AA, 32% Aa, 4% aa
Suppose that kin selection is acting upon a group of rodents. The average female typically has four offspring in her lifetime. If, instead of raising her own offspring, a female helps her sister raise her offspring (i.e. her own nieces and nephews). How many offspring would her sister have to have in order for her to experience no net loss in fitness?
8
In a population of Mendel's garden peas, the frequency of green-flowered plants (genotype aa) is 49%. The population is in Hardy-Weinberg equilibrium. What are the frequencies of the AA and Aa genotypes?
9% AA, 42% Aa
What contributes to your physical fitness?
A balanced diet and heavy lifting at the gym
Founder effect
A population where a group of individuals discover a new niche and settle a new population somewhere. DECREASE IN GENETIC VARIATION OF POPULATION
When individuals from East 1 and East 2 mate, their offspring are very small and unable to eat seeds of any size. As a result, the hybrid offspring die before they can produce offspring. This is an example of
A post-zygotic isolating mechanism
What contributes to your overall fitness (Inclusive fitness)?
All genes you pass to your offspring and those you share with your non-offspring relatives. Diet + Indirect fitness
Eventually, enough time has passed that West and East are genetically distinct from one another, and they can no longer interbreed. Which form of speciation has occurred
Allopatric Speciation
f(B)=p=.127 f(b)=q=.873 what genotypes will we see (next gen)
BB=.127^2=.016 Bb=2(.127)(.873)=.222 bb=.873^2=.762
Why is it likely that MOST speciation is allopatric?
Because gene flow between populations prevents genetic divergence in sympatry.
What occurs as genetic Drift?
Bottleneck effect and founder effect
If reinforcement of post-zygotic isolation is occurring, what would you expect if you compare the calls of the two species in zones of sympatry versus zones of allopatry?
Calls would be more different in areas of sympatry.
A predator recognizes large and small peacock tails but not intermediate sized tails
Disruptive
Which form of selection would you expect in pop East for surface area for grinding on teeth (for eating the new seeds)?
Disruptive selection
Traits do not have to be heritable to be selected for
False
If a population has low genetic variation, it is more susceptible to genetic drift
False: Opposite of that
A population with low genetic variation is more susceptible to genetic drift
False: drift tends to reduce genetic variation
Natural Selection leads to differential survival and identical reproduction of individuals
False: it doesn't lead to identical reproduction
Natural selection itself is a stronger force in larger populations than in small populations
False: not necessarily (dependent mostly on variation)
natural selection itself is a stronger force in large populations than in small pops
False: ns can be more effective in large pops because beneficial alleles are less likely to be lost do to drift, but the strength of selection is not dependent upon pop size
RANDOM changes (not about more fit traits). more likely with small popualtion
Genetic Drift
As soon as the two populations are separated, which the following will have the greatest effect on divergence between two populations
Genetic drift
The faster rabbits w/ 'F' allele are able to travel long distances. A group of fast rabbits deviate from their native locations and discover a new niche where they settle and start a new population. WHAT IS THE EVOLUTIONARY DRIVING FORCE BEHIND THIS
Genetic drift--> founder effect
1. Ancestors of each of the five current island species dispersed from the mainland to the island, subsequently diverging from mainland species ("dispersal hypothesis"). 2. The island was originally part of the mainland, but a rise in sea level caused it to become isolated. Then island mammals diverged from their mainland ancestors ("vicariance hypothesis"). How would you distinguish between these two hypotheses after sequencing the same segment of DNA in each of the 10 species?
If the amount of genetic divergence between species in all five pairs is similar, then vicariance is the likely cause.
A form of natural selection where one sex attempts to attract the attention of the opposite sex for reproduction is called------selection
Intersexual selection )female choice)
A form of natural selection where males compete with other males for access to the opposite sex for reproduction is called-----selection.
Intrasexual Selection (male competition)
When we look at islands across the planet (think the islands of the Galápagos and Hawaii) we see that there are a remarkable number of island endemic species, species that are found nowhere else. What is a possible explanation for this observation?
Island isolation promotes allopatric speciation.
Bottleneck effect
Major disaster that kills a majority of the population. Random chance they survive, not because they have any desirable traits. DECREASE IN GENETIC VARIATION OF POPULATION
The fast rabbits have more access to food resources than the slow rabbits due to their overall ability to travel farther distances. They have exclusive access to carrots that have been constantly irrigated with toxic waste. Overtime the rabbits with the 'F' allele decrease in frequency due to death. What evolutionary driving force is this?
Mutation
Imagine the following genotype frequencies in a population: p2 = 0.49, 2pq = 0.42, q2 = 0.09. Now assume that there is nonrandom mating where individuals with one genotype will only mate with individuals that also have their genotype. Assume this pattern of mating goes on until the frequency of heterozygotes is effectively zero. Is this population in Hardy-Weinberg equilibrium?
No, because there is nonrandom mating.
What contributes to indirect fitness?
Only genes you share with your non-offspring relatives
What contributes to your direct fitness?
Only the genes that you pass to your offspring
Mode of speciation in which a new species is formed from an isolated peripheral population. Separated by in extreme change in habitat
Peripatric Speciation
an individuals observable characteristics
Phenotype
Example of genetic drift:
Rabbits have a certain frequency of "B" and "b". By chance they reproduce and the "B" gene frequency decrease while the "b" gene decreases. By chance they reproduce again and the "B" gene increases again eventually leading to "b" not being in the population anymore at all
Inbreeding depression is a serious concern in small populations of endangered organisms. Why is inbreeding depression a concern for such populations?
Related individuals are more likely to mate with one another and this increases the probability that two deleterious alleles will be present in the offspring.
Female rabbits are more attracted to faster rabbits because it portrays the male as a healthy individual, thus rabbits who have the 'F' allele will mate more often and produce more offspring and overtime this will cause the 'S' allele to decrease in the population, WHAT IS THE EVOLUTIONARY DRIVING FORCE BEHIND THIS?
Sexual selection
A large population of mice (2000 individuals) lives in an area dominated by small shrubs in the desert. When the population size got too high, a small group of 6 individuals left and colonized an area adjacent to the original population's home, but this area is primarily dominated by trees instead of shrubs. There is no gene flow between the dispersers and the original population. A researcher sequenced the genomes of representative individuals from both populations and found substantial genetic differences between them. Which of the following would MOST account for the amount of genetic differences observed?
Since the original dispersal event, the small population will have evolved more than the large population.
Which of the following statements is always TRUE about sister taxa on a phylogenetic tree?
Sister taxa always share a most recent common ancestor that is not shared with any other taxon on the phylogeny.
Which modes of selection will not necessarily change the mean trait value in a population?
Stabilizing: intensifies the mean Disruptive: effects are cancelled out due to both extremes present, so no effect on mean
Individuals only mate with other individuals that eat the same size seeds in their pop. Over time, two new species, East 1 and East 2, develop from the original eastern population. This is the result of ------ speciation
Sympatric
The process through which new species evolve from a single ancestral species while inhabiting the same geographic region. Most commonly occurs from polyploidy in which an offspring or group of offspring will be produced with twice the normal amount of chromosomes
Sympatric Speciation
What is the significance of the accumulating genetic differences between West and East?
The two populations are becoming genetically distinct from each other
The graph in Figure 22.9, below, shows that the extent of the adaptive radiation of the Galápagos finches is correlated with the number of islands present in the archipelago. What can be concluded from the graph?
This shows that opportunities for geographic isolation are a key component of the speciation process.
A species consists of individuals who exchange genetic materials through interbreeding
True
Genetic drift can occur in the absence of population bottlenecks or founder effects.
True
It is possible for large populations to have low levels of genetic diversity
True
Traits that are preserved through natural selection are called adaptations
True
Natural selection is not the only process for evolution
True: 3 more--> drift, migration, mutation
When individuals from species East1 and East2 mate, their offspring are underdeveloped and unable to eat seeds of any size. As a result, the hybrids die before they can produce their own offspring. This is an example of:
a post-zygotic isolating mechanism.
Individuals ------ , while populations ----- over time
acclimate; adapt
after mass extinction events, resources and land open up to new species. due to this huge abundance of available niches, many new organisms can come fill those niches and diversify.
adaptive radiation
one form of a gene
allele
What is the diff between allopatric and sympatric speciation
allopatric is the separation of 2 pop to create two species while sympatric is speciation without a physical barrier (evoloving from a single ancestor but live together) gene flow is still present
Eventually, sufficient time has passed that West and East are genetically distinct from one another, and they could no longer interbreed if they came in contact. Which form of speciation has occurred?
allopatric speciation
Different species of fruit flies occupy each of the islands in the Hawaiian island chain, a group of volcanic islands that formed one after the other. One hypothesis for how the different fruit fly species formed is that, after each new island was formed, fruit flies from existing islands colonized it and subsequently diverged. If this hypothesis is correct, it would be an example of:
allopatric speciation by dispersal.
a trait that evolved independently (no common ancestry)
analogous trait
Both prezygotic and postzygotic factors are mechanisms of reproductive isolation! if any of these factors occur, two groups are defined as separate species by ---- species concept
biological
In simple terms, evolution would be ----- and natural selection is the ---- of change
change; mechanism
Disruptive Selection
changes in population genetics in which extreme values for a trait are favored over intermediate values. variance of the trait increase and the population is divided into two distinct groups
what is the diff between cladogram and phylogram and chronogram
cladogram--> branching pattern (evolutionary relationships) phylogram--> horizontal branch length (extent of genetic diff) chronogram--> horizontal branch length (extent of evolutionary btwn nodes)
nodes represent---, and branches can be rotated around the node in any way to depict the ---- tree
common ancestors; same
In the summer inc temp causes all the snow to melt and white rabbits lose their benefit of camo. assuming everything else in the environment is still the same, what type of selection is being shown now.
directional
King crabs with larger pinchers are better able to hunt for food than crabs with middle or small
directional
In general, sympatric speciation requires the action of _____ selection acting against hybrids.
disruptive
In population East, which mode of selection would you expect to act upon grinding surface area on teeth (for eating the new seeds)?
disruptive selection
on an island there is a species of rabbit that varies along a spectrum of fur coat color. There is a thick layer of snow that covers the floor of the island and also many dark tree trunks and patches of dark soil, therefore, rabbits with black coats and white coats are able to camouflage with their environment and avoid their predators, and these coat colors are selected for
disruptive selection
If a population is not in Hardy-Weinberg equilibrium, we can conclude that:
evolution has occurred because one or more of the assumptions of the Hardy-Weinberg equilibrium has been violated.
the length of a branch in a phylogenetic tree represents --- ----- or ----
evolutionary distance; time
phylogenetic trees depict a hypothesis of ---- relationships using any ---- trait
evolutionary; genetic
Directional Selection
extreme phenotype is favored over the other, causing allele frequency to shift over time in the direction of that phenotype
Over time the freq of a dom allele gradually increase
false
Researchers sequence 10,000 bp of dna from multiple loci in each species and compare the number of base pair differences between each species pair (A compared to B, C compared to D, and E to F). To rank the species pairs in order of greatest number of base pair differences to fewest number the base pair differences pacific 1 (a)= .5-.1m caribbean 1 (b)= .5-.1 pacific 2 (c)= 2-4 caribbean 2 (d)= 2-4 pacific 3 (e)= 6-8 caribbean 3 (f)= 6-8 -the number of diff should be greatest between p1 and c1, and the fewest should btwn p3 and c3
false: both are the same
the effects of genetic drift are not population size dependent
false: dependent on variation
gene flow is a mechanism of evolution in which allele freq in the gene pool change due to chance
false: migration
mutations can only be deleterious or advantageous
false: neutral
what is favored by sexual selection is also favored by natural selection
false: think of peacock example
p^2+2pq+q^2=1 can be used to calculate allele frequencies from genotype freq
false: this only works if you know the pop is in HW eq
Stabilizing Selection
favors the intermediate variants. It reduces phenotypic variation and maintains the status quo
Compared with more distantly related taxa, the DNA sequences of two closely related taxa are expected to show:
fewer differences because mutation rates are usually relatively constant and recently diverging species have had less time to accumulate differences.
Which mechanism of evolution is the only one that makes pop more genetically similar
gene flow
total collection of genes in a pop at any one time
gene pool
New species can form through allopatric or sympatric speciation. Which of the following mechanisms will act more strongly on populations that are initially separated in allopatry than on those initially separated in sympatry?
genetic drift
upon separation, which will have the greatest effect on divergence between the two populations?
genetic drift
genetic diff that exist among individual sin a population at a particular time
genetic variation
genetic makeup of an organism
genotype
phylogenies
go to worksheet 5/ wk 6 (#12-13)
Phylogeny question
go to worksheet 5/ wk 6 (#2-4)
a trait with common ancestry
homologous trait
a trait similar in form between species, but did not derive from a common ancestry
homoplasy
In some large groups of plants, including dandelions, oaks, and willows, the biological species concept is complicated because the process of _____ allows gene flow to occur between good _____ that can be easily distinguished based on appearance.
hybridization; morphospecies
Natural selection acts on the ----, and evolution acts on the -----
individual; population
Sympatric Speciation
is the process through which new species evolve from a single ancestral species while inhabiting the same geographic region.
group that includes common ancestor and all the descendants
monophyletic group
what was the origin of the unique alleles in each of the subpops
mutations that occur randomly throughout the genomes of individuals in each subpop
You notice a population of 100 flowering plants that all look identical (phenotypic clones), spanning an area of 100 square meters (m2). You collect samples from every individual, sequence their DNA and determine that they are diploid and also genetic clones. -Can this population evolve via natural selection
no
There are two alleles C and c. C codes for green hair and c codes for white hair. C is dom over c, so the heterozygous state individuals will have green hair. The freq of the c allele is .3. Assuming the pop is in H-W equilibrium what are the genotype freqs?
p=.7 q=.3 1. determine the other allele freq: 1-.3=.7 (p+q=1) 2. what are the possible genotype combos: CC--> p^2: (.7)^2= .49 Cc--> 2pq: 2(.3)(.7)= .42 cc--> q^2: .3^2= .09
in a pop of 100 individuals there are 36 individuals with white hair. What are the allele frequencies of C and c, how many individuals have the genotype CC
p=C q=c 1. we know from previous question that q^2=cc so q^2=.36 --> q=sqrt(.36)= .6 *allele freq* 2. p+q=1 --> p + .6= 1 p= .4 *allele frequency* 3. freq of CC --> p^2: .4^2= .16 *genotype freq* 4. 100--> CC .16(100)= 16 individual shave CC
hardy weinberg equations
p^2 + 2pq + q^2= 1 p + q= 1 p=freq of dom allele in pop q=freq of recessive allele in pop
most likely explanation is the one with lease number of evolutionary changes
parismony
a group with descendants but no common ancestors
polyphyletic group
If hybrids formed between individuals from East1 and East2 and had equal fitness to either parental species, this would:
preclude speciation between East1 and East2.
For reciprocal altruism to work, individuals must be able to:
recognize one another and remember previous interactions.
If we assume stabilizing selection maintains a balance between predation avoidance and energy requirements in mainland gray foxes, why are their descendants smaller on the channel islands
resources are more limited on islands and islands often lack mainland predators
Reinforcement is
selection against hybridizing behavior between individuals from diverging populations
Mutations can be -------, occurring in the body's tissues, or ------, occurring in the reproductive cells and therefore passed on to the next generation. From an evolutionary viewpoint, we are primarily interested in ------ mutations
somatic, germline, germline
In regards to birth weight, mortality rates are high for very small babies and very high for large babies
stabalizing selection
Finches with middle sized beaks are able to eat seed of all sizes
stabilizing
Individuals only mate with other individuals that eat the same size seeds in their population. Over time, two new species, East1 and East2, develop from the original eastern population. This is the result of ________ speciation.
sympatric
All else being equal, selection should more strongly favor reinforcement of reproductive isolation among related species in:
sympatric populations over allopatric populations.
a shared, derived characteristic
synapomorphy
bottleneck and founder effects are two types of genetic drift
true
mutations always occur by chance and are random
true
Sympatric specieation can result from ---- selection. How?
we get two distinct sub-pop within pop, start to diverge to become two distinct populations (morphospecies concept)
