Exam 1 Flashcards
1
Q
What is evolution?
A
A change in allele frequency over time.
2
Q
What are the two ways that evolution can occur?
A
1) Natural Selection
2) Artificial Selection
3
Q
What is Natural Selection?
A
The process in which, when there is genetic variation in a population of organisms, the variants best suited for growth and reproduction in a given environment contribute disproportionately to future generations.
4
Q
What is the only evolutionary mechanism that can lead to adaptation?
A
Of all the evolutionary mechanisms, natural selection is the only one that leads to adaptations.
5
Q
What is artificial selection?
A
A form of directional selection similar to natural selection, but with selection done intentionally by humans, usually with a specific goal in mind, such as increased milk yield in cattle.
6
Q
What is a gene?
A
A section of DNA that influences 1or more hereditary traits
7
Q
What is an allele?
A
Different versions of a gene.
Different alleles are responsible for variation in traits
8
Q
What is a genotype?
A
The combination of alleles found in an individual.
9
Q
What is a phenotype?
A
An individual’s observable features.
An individual’s genotype has a profound effect on phenotype.
10
Q
What is fitness?
A
The ability of an individual to produce surviving fertile offspring relative to that ability of other individuals in the population.
11
Q
What is adaptation?
A
A heritable trait that increases an individual’s fitness in a particular environment.
Individuals who are best adapted are more likely to survive and produce offspring.
12
Q
True/false:
It is genetic variation among individuals that results in some individuals that are more likely to survive and reproduce, passing their genetic material to the next generation.
A
True
13
Q
What are Darwin’s 4 postulates?
(be able to apply to determine if evolution has taken place)
A
- Individuals in a population vary in their traits.
- Some of these differences are heritable; they are passed on to offspring.
- In each generation, many more offspring are produced that can survive.
- Individuals with certain traits are more likely to survive and reproduce.
- natural selection occurs when individuals with certain traits produce more offspring than do individuals with out those traits.
- the individuals are selected naturally by the environment.
14
Q
True/false: evolution by natural selection occurs when heritable variation leads to differential reproductive success.
A
True.
15
Q
True/false: it is populations that evolve, not individuals.
A
True.
16
Q
Natural selection acts on individuals because it is individuals in the population that experience _________________
A
Differential reproductive success.
17
Q
True/false: evolution leads to perfectly adapted organisms.
A
False
18
Q
What lines of evidence support the theory of evolution by natural selection?
A
1) fossils provide evidence of organisms that have lived in the past, and may now be extinct. (>99% that have ever lived are now extinct). The fossil record provides evidence that species are dynamic and have changed through time.
2) transitional features: traits that are intermediates between ancestral and derived species. This provides strong evidence of change in traits through time.
3) homoloy: descent from a common ancestor. A similarity that exists in a species descended from a common ancestor. Homologies can be genetic, developmental and structural.
4) vestigial traits are common. E.g. tails and gill slits in human embryos
5) characters within populations vary and can be observed changing today. Evolution is observable.
6) similar species often live in the same geographic area.
19
Q
What are the 3 ingredients necessary for natural selection?
A
1) variability
2) heritability
3) reproductive advantage
If any of these are missing, then it’s not natural selection.
20
Q
What is the difference between Acclimatization and adaptation?
A
Acclimatization: phenotype changes in response to environment (e.g. getting used to altitude) and is not passed along to offspring.
Adaptation occurs when the allele frequencies in a population change in response to natural selection
21
Q
What is a vestigial trait?
A
A reduced or incompletely developed structure that has no/reduced function
22
Q
True/false: all traits are adaptive.
A
No. All traits, even adaptive ones are constrained by genetic and historical factors.
All trains evoke from previously existing traits so adaptations are constrained by history.
23
Q
Why is maintaining genetic variation important?
A
1) selection can only occur if heritable variation exists
2) lack of variation can make populations less able to respond successfully to changes in the environment, and their average fitness will decline
3) if environmental change is severe, the population may become extinct
24
Q
What are the 4 modes of selection that affect genetic variation?
A
1) directional selection
2) stabilizing selection
3) disruptive selection
4) balancing selection
No matter how selection occurs, it increases fitness and leads to adaptation.
25
Directional selection
-changes the average phenotype in the population in one direction.
- tends to reduce the genetic variation of a population.
- changes the the average value of a trait. Graphically it is a shift in the bell curve. Favors an extreme phenotype causing the population to change in one direction.
26
What is positive selection?
Natural selection that increases the frequency of an advantageous allele. (Darwinian selection)
27
What is negative selection?
Selection that decreases the frequency of deleterious alleles. (Purifying selection)
28
Stabilizing selection
- reduces extreme phenotypes in the population and favors intermediate phenotypes.
- does not change the average value of a trait
-tends to reduce the amount of genetic variation in a population because alleles for extreme phenotypes could be lost
-graphically the bell curve is not shifted in one direction or the other. Instead, it is squished.
29
Disruptive selection
- the opposite of stabilizing selection. Favors extreme phenotypes and selects against intermediate phenotypes.
- increases genetic variation by maintaining the extreme phenotypes
-can cause speciation if strong enough (sympatric speciation)
- graphically the bell curve has a depression in the middle because intermediate are not favored while the extremes at both ents of the curve are.
30
Balancing selection
-occurs when no single allele has a distinct advantage
-genetic variation is maintained
- can occur in 3 ways:
1. Certain allies are favored at different times or places (although allele frequency change locally, overall genetic variation in the population is maintained)
2. Heterozygous individuals have higher fitness homozygous individuals do (heterozygote advantage, e.g., malaria, hemoglobin)
3. Certain alleles are favored when they are rare, but not when they are common (e.g. guppy tail color - predation)
- graphically there is no change in the bell curve
31
What is a fitness trade off?
A compromise between traits in terms of how those traits perform in the environment.
Because evolution acts on many traits at once, every adaptation is a compromise
32
True/false: mutation is the only source of genetic variation.
False (horizontal gene transfer exists)
33
Evolution (the change in allele frequencies) is driven by what 5 processes?
1. Natural selection
2. Genetic drift
3. Gene flow
4. Mutation
5. Horizontal gene transfer
34
Mutation (Germ line)
- The raw material on which natural selection acts
- it is the random production of new alleles
- it increases genetic variation by producing new alleles
- it is random with respect to fitness but mutations in coding sequences usually lower fitness as most mutations are deleterious.
- without mutation, evolution would eventually stop.
- mutation alone is usually inconsequential in changing allele frequencies at a particular gene.
35
Genetic Drift
- any change in allele frequencies in a population due to chance. Causes allele frequencies to drift up or down over time.
- it is random with respect to fitness, usually reduces avg. fitness. Doesn’t result in adaptation.
- larger effect on small populations (like a coin flip)
- caused by any event that involves sampling error (e.g., founders effects and bottlenecks)
- tends to reduce genetic variation via a loss or fixation of alleles.
36
What is a founder effect?
Occurs when a group of individuals establishes a new population In a new area.
- allele frequencies likely differ from the source population if the new population is small enough
- common in the colonization of isolated habitats such as islands.
37
What is a population bottleneck?
A sudden decrease in population size in a large population. The bottlenecked population likely has different allele frequencies from the original by chance)
- commonly caused by disease outbreaks and natural catastrophes.
- leads to genetic bottlenecks.
38
What is a genetic bottleneck?
A sudden decrease in the number of alleles in a population.
-genetic drift occurs in genetic bottlenecks and causes a change in allele frequencies
39
What is gene flow?
The movement of alleles between populations.
- occurs when individuals leave one population, join another and breed.
-tends to homogenize populations, reducing genetic variation
- random with respect to fitness. Lowers the fitness of captive bred and wild populations
40
Horizontal gene transfer ( what is it and what are the three ways it can happen).
Transfer of genes from one individual to the next that are not parent or offspring.
-Can happen in 3 ways:
1. Conjugation
2. Transformation (dna taken up from environment)
3. Transduction (dna transferee from virus)
41
Which of the following statements would Darwin have agreed with? Select all that apply.
1)There are higher and lower organisms.
2)Descent with modification occurs through inheritance of acquired characteristics.
3)Variation between individual within a population is essential.
4)Living species have arisen from earlier life-forms.
3 and 4
42
Genetic variation ________.
A) arises in response to changes in the environment
B) tends to be reduced by when diploid organisms produce gametes
C) is created by the direct action of natural selection
D) must be present in a population before natural selection can act upon the population
D
43
Over long periods of time, traits can be lost in a population. Whales have lost their hind limbs. Tapeworms have lost their digestive systems. Many cave-dwelling organisms have lost their eyes. How can natural selection account for these losses?
A) Natural selection cannot account for losses but accounts only for new structures and functions.
B) The ancestors of these organisms experienced harmful mutations that forced them to lose these structures.
C) Natural selection accounts for these losses by the principle of use and disuse.
D) Under particular circumstances that persisted for long periods, each of these structures presented greater costs than benefits.
D
44
True/false: An individual can acclimate, but only populations can adapt
True
45
True/false: Whether or not an organism survives and ultimately reproduces is almost entirely a matter of random chance
False
46
True/false: Natural selection always increases fitness of a population by maintaining genetic variation.
False
47
True/false: Natural selection starts with the creation of new alleles that are directed toward improving an organism's fitness.
False
48
True/false: Natural selection and evolutionary change can occur in a short period of time (a few generations).
True
49
True/false: Natural selection depends on the local environment at the current time.
True.
50
Individual females within a population of cattle are tracked over time to examine their reproductive output. The researchers find that females with the smallest and largest body sizes have fewer offspring than females of average body size.
What type of selection depicts what is going on in the scenario above?
Stabilizing selection (extremes are being selected against).
Genetic variation is is decreasing because extreme alleles might be lost
51
This evolutionary process always increases genetic variation by producing new alleles, however, it is typically neutral or reduces fitness.
Mutation
52
This evolutionary process always reduces genetic differences between populations, which can increase or decrease the fitness of the populations.
Gene flow
Can increase by introducing new alleles or it can decrease by homogenizing the populations.
53
This evolutionary process is driven by differential reproductive success.
Natural selection
54
This evolutionary process is the random change of allele frequencies over time.
Genetic drift
55
Which of the following could lead to balancing selection in a population? Select all that apply.
1) When heterozygous have an advantage over homozygous individuals
2) When certain alleles are favored when they are common
3) When one phenotype always has a higher fitness than other phenotypes
4) Frequency-dependent selection
1 and 4
56
What is frequency dependent selection l?
When certain alleles are favored when they are rare. Not when the are more common.
Can result in balancing selection.
57
What are the two modes of reproduction?
1. Sexual reproduction
2. Asexual reproduction
58
What is asexual reproduction?
It occurs through mitosis and and produces offspring which are genetically identical to one another and to their parent (barring mutations).
All prokaryotes reproduce asexually. Some eukaryotes reproduce asexually
59
What is sexual reproduction?
Occurs through meiosis and produces offspring that are genetically distinct from one another and their parents.
Offspring are the result of genetic recombination of the two parental lines.
Nearly all eukaryotes reproduce sexually. No prokaryotes reproduce sexually
60
What unique character defines the biological sexes?
Males have smaller gametes than females (it is not X and Y because that character is not universal)
61
What is ploidy?
A cells ploidy indicates the number of complete sets of chromosomes (e.g., 2n where n = number of chromosomes present)
Diploids (2n) have 2 sets of chromosomes and two alleles of each gene
Haploids have one chromosome set and just one allele of each gene.
Ploidy changes during the life cycle of an animal
62
What is the difference between Mitosis an meiosis?
Which one results in genetically unique cells and why?
Mitosis = results in two genetically identical diploid cells. Used in growth, repair and asexual reproduction
Meiosis = results in 4 genetically unique haploid cells. It is used for sexual reproduction.
Genetic recombination occurs during meiosis and is why offspring are genetically distinct and unique in sexual reproducing organisms
63
What are the 3 types of life cycles?
1. Haplontic
2. Diplontic
3. Haplodiplontic (alternation of generations)
64
What is a haplontic life cycle?
Adult Organism lives it’s life as a haploid.
Organism can be single or multicellular
Meiosis produces spores.
N gametes—> 2n zygote—> meiosis produces spores (n) —> mature organism (n)
65
What is a diplontic life cycle?
Mature organism lives it’s live as a diploid.
Haploid gametes—> 2n zygote—> mature organism—> n gametes
66
What is a haplodiplontic life cycle?
Mature organism is multicellular diploid or haploid. Has multicellular stages at haploid and diploid stages
N gametes—> 2n zygote—>multicellular diploid—> meiosis produces spores n
67
What is the twofold cost of sex?
In sexual reproducers 1/2 the population cannot produce offspring. In asexual reproduction all individuals can produce offspring, so the double their number each generation.
Other factors that contribute to the cost of sex are: finding a mate, courtship, cost of meiosis
68
What are the two most likely hypotheses as to why is sex maintained as a method of reproducing?
2 hypotheses:
1) in environments where evolving pathogens are present, sexual reproduction by outcrossing will be favored.
2) faster reduction of accumulating deleterious mutations. In asexual reproduction a damaged gene will be inherited by all offspring. This is not the case with sexual reproduction.
69
What is Muller’s ratchet?
Genomes of strictly asexual organisms are fated to accumulate mutations that are mostly deleterious to survival in a ratchet like manner (mutations get locked in, organism can only escape effects through back mutation which is very rare).
Ultimately enough deleterious mutations accumulate and organism undergoes mutational meltdown.
Sexual reproduction counters mullers ratchet. Genetic recombination in meiosis can result in a recovered wild type.
70
How can strictly asexual organisms avoid mullers ratchet?
Horizontal gene transfer
Genetic recombination is essential for all life forms
71
What are some strategies organisms have adopted to reduce the twofold cost of sex?
1. Sex switching when environmental conditions change.
2. Having a sexual and asexual life cycle.
3. Increase paternal investment allowing an increase in offspring
72
True/false: In sexual reproduction, gametes are only produced by meiosis.
False.
73
True/false: Some sexually reproducing organisms have adaptations that reduce the 2fold+ cost of sex, such as reducing the build up of deleterious mutations.
False. Reducing the number of deleterious mutations is not one of the 3 ways to reduce the cost.
74
True/false: Sexually reproducing organisms pay the 2fold+ cost of sex because of constant environmental changes such as parasites and pathogens.
True.
75
Which of the following statements about sexual reproduction and genetic recombination are TRUE? Select all that apply.
1)Since prokaryotes do not reproduce sexually, they do not have any form of genetic recombination.
2) Sexually reproducing organisms pay the cost of sex because of constant environmental changes such as droughts and floods.
3) Having an asexual portion of your life cycle can reduce the cost of sex.
4) The 2fold+ cost of sex includes the cost in finding a mate.
3 and 4
76
When does speciation occur?
When two populations are no longer able to produce viable, fertile offspring.
77
What are the 4 main species concepts?
1. Biological species concept
2. Morphospecies concept
3. Ecological species concept
4. Phylogenetic species concept
78
The Biological species concept states_____. It’s advantageous and disadvantages are______.
The main criterion for identifying species is reproductive isolation
Advantages: it is undisputed that 2 species that can’t produce viable, fertile offspring are different species
Disadvantages:
1. More useful in theory than practice, can’t always test whether 2 organisms are reproductively isolated
2. Does not apply to asexual or extinct species
3. Hybridization (incomplete reproductive isolation) complicates matters.
79
What are the two mechanisms that can stop gene flow between populations?
1. Prezygotic isolation
2. Postzygotic isolation
80
What is prezygotic isolation and what are some examples?
Happens prior to formation of a zygote. Individuals of two different species are prevented from mating successfully.
Prezygotic barriers include: habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation
81
What is postzygotic isolation and what are some examples?
Happens after zygote formation. Offspring do not survive or do not reproduce.
Postzygotic barriers: reduced hybrid viability (short lived), reduced hybrid fertility, hybrid breakdown (fertile hybrids with sterile offspring)
82
The Morphospecies concept states ______. It’s advantages and disadvantages are_____.
Individual lineages differ in size, shape, or other morphological features. Distinguishing features most likely arise if populations are independent and isolated from each other.
Advantage: it is widely applicable. Useful when there is no other data on the extent of gene flow. Applicable to to sexual, asexual and fossil species.
Disadvantages:
1. Polymorphic species might be classified as more than one species.
2. It cannot identify cryptic species that differ in non-morphological traits (differences at the dna sequence)
3. The features used to distinguish species are subjective (are the different enough to call them a new species?)
83
The Ecological species concept states_____. It’s advantages and disadvantages are______.
A species is a set of organisms that is adapted to a particular set of resources (niche) in the environment.
Advantages: applies to asexual organisms such as bacteria on basis of their similarities or differences in their ecological requirements
Disadvantages:
1. Does not apply to fossil species
2. Can be challenging to apply- a lot of resources needed to gather all the data required
84
The Phylogenetic species concept states _____. It’s advantages and disadvantages are______.
Identifies species based on evolutionary history
Advantages: it is broadly applicable. The data going into the tree can be anything that is robust enough to construct a tree
Disadvantages:
1. Trees can be difficult to produce. You can get different trees depending on what data are used
85
What is allopatric speciation?
Speciation that begins with geographic isolation.
86
What are the two ways geographic isolation can occur
Dispersal and vicariance.
87
How does Allopatric speciation by dispersal work?
Some individuals disperse from their population and colonize a new habitat.
The new population (smaller) begins to diverge due to mutation, genetic drift and selection.
Eventually the two populations are genetically isolated from each other
88
What is Allopatric speciation by vicariance?
1. A chance event physically separates the population into two subgroups
2. Isolated populations begin to diverge due to mutation, genetic drift, and selection
3. Eventually the two populations are genetically isolated from each other
89
Sympatric speciation
Occurs in populations that live in the same geographic area close enough to interbreed.
1. No geographical separation
2. New population begins to diverge because of selection
3) eventually the two populations are isolated from each other
90
What are the two mechanisms of sympatric speciation?
1. Strong disruptive selection
2. Polyploidization - the number of chromosomes gets messed up. Can be during meiosis or mitosis.
91
If speciation is occurring, which evolutionary process is not occurring (least likely) between the two populations?
Gene flow
Genetic drift
Natural selection
Disruptive selection
Gene flow
92
Sympatric speciation: (select all correct answers)
1) occurs when two populations have constant gene flow
2) occurs whenever a physical barrier between two species is removed (i.e., a river dries up) and the two species start to interbreed.
3) can occur instantaneously through formation of polyploid offspring.
4) only occurs in bacteria.
3
93
A researcher notices that in a certain moth species, some females prefer to feed and lay eggs on domesticated solanaceous plants like potatoes and tomatoes. Other females prefer to feed and lay eggs on wild solanaceous plants like Datura. Both male and female moths primarily use scent to find these plants from afar. All of these solanaceous plants occur in the same meadow. Females tend to mate where they feed, and the researcher finds a genetic basis for scent preference in these moths.
Based on the above information, ______________ could be occurring in this moth population.
Sympatric speciation
Allopatric speciation by vicariance
Allopatric speciation by dispersal
Sympatric speciation
94
What are sister taxa?
Groups that share a recent common ancestor
95
How are phylogenetic trees built?
They are built using shared derived characters (synapomorphies).
A character is any genetic, morphological, physiological or behavioral characteristic to be studied
96
What is an out group?
A sister group that shared a common ancestor with taxa being studied, but is not part of the study group.
Used to root the tree
It tells us what the the last common ancestor of our group looked like and then what happened and what has changed since then.
97
What is an Ancestral trait and what is a derived trait?
Ancestral trait= a character that existed in an ancestor.
Derived trait= one that is a modified form of the ancestral trait found in a descendant.
Ancestral and derived traits are relative- they depend on what taxa is being studied.
98
When certain data are not available, how should we chose the best tree?
Use the principle of parsimony. The tree with the least amount of change is likely the one that most accurately reflects what occurred during evolution
99
What is the molecular clock and what does it measure? How is it calibrated?
The correlation between time and the amount of genetic divergence that has taken place. It measures genetic divergence over time.
It is calibrated using the fossil record.
Rates of molecular clocks vary between genes because of the intensity of negative selection. If virtually all mutations in a certain geo are selected against, the rate of molecular evolution is very slow.
100
What is a monophyletic group?
A group that includes a common ancestor and all of its descendants
101
What is a Paraphyletic group
Includes a common ancestor and some but not all of its descendants
102
What is a polyphyletic group?
A group that does not include the common ancestor
103
What is a Homologous character? What is an analogous character?
Homologous character= characters that are similar due to shared ancestry.
Analogous Character = characters that are similar for reasons other than common ancestry (arose through convergent evolution- when selection favors similar solutions to similar environmental pressures)
Only homologous characters can be synapomorphies.
104
How do we know if a trait is homologous or analogous? What are the four lines of evidence used?
1. Structural evidence
2. Genetic evidence
3. Developmental evidence
4. Phylogenetic evidence
Agreement of all four types provides strong evidence for homology.
105
Which of these hypotheses have NOT been suggested as a foundation for the origins of life?
1)The basic molecules that form the fundamental biological building blocks of life can be synthesized on meteorites in outer space.
2) The molecules that form the building blocks of life arose as a result of combustion of diatomic oxygen (O2) in the ocean providing energy to form simple organic compounds.
3)The energy from lightening resulted in simple organic compounds to form in the atmosphere that rained down into the ocean.
4) Energy from deep sea hydrothermal vents provide the energy for chemical reactions necessary to form molecules that are fundamental biological building blocks of life.
2
106
Which of the following characteristics is evidence that all of life shares a last universal common ancestor (LUCA)? Select all that apply.
1)The genetic code
2)The use of DNA to store genetic information
3)The central dogma
4)The use of the same enzymes for central metabolic pathways
All of them
107
Evidence in support of life emerging over 3,500 MYA comes in part from several observations, but this is NOT one of them
A) Fossils in carbonate that appear to look like individual microbes
B) Observations of 13C/12C ratios consistent with of 13C/12C ratios values produced by life today
C) Observations of stromatolite fossils
A
108
What is one way we can determine the amount of time between divergence of species?
Using the molecular clock.
109
What is coevolution and can phylogenetic relationships be used for examining coevolutionary relationships?
Coevolution is the process in which species evolve together, reach responding to selective pressures from the other. One population influences the evolutionary trajectory of the other.
Yes. Phylogenetic analysis can be used to examine coevolutionary relationships.
110
True/false: DNA sequences can be used as characters for constructing phylogenetic trees. Why or why not?
True.
Because similar DNA sequences are not likely to be analogous.
111
All life forms on earth are made up of cells. What other characteristics does all life on earth share? (Biochemically)
- all cells are surrounded by a cell membrane composed of fatty molecules.
- life uses DNAa and RNA as the genetic material and genetic expression
- all life uses amino acids to build proteins and enzymes to carry out most functions
- all life uses the same genetic code to translate between DNA —>RNA—>proteins
- all life uses the same central metabolic pathways.
112
Only_________groups represent the true evolutionary history of a species
Monophyletic groups
113
_________ are the earliest evidence of life on earth and you can still find them today (e.g the great salt lake).
Stromatolites (rocks formed by living organisms).
114
What are isotopes and how are they used in biology?
Isotopes are elements of the same kind, but differ in the number of neutrons. C12 and C13 occur naturally.
If a rock is formed by a geological process the C13/C12 ratio is 0.0113
If a rock is formed by a biological process the C13/C12 value is 0.01095
