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Biology 180 > Biology 180: Exam 2 > Flashcards

Biology 180: Exam 2 Flashcards

1
Q

Directional Selection

A

Allele frequency changes in one direction

Selection favors one end of the phenotypic range – those become more common – and reduces the other extreme

The average value of the trait in the population changes towards one end and the genetic diversity of the population is reduced.

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2
Q

Purifying Selection

A

Selection that lowers the frequency or even eliminates deleterious alleles

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3
Q

Stabilizing Selection

A

Selection acts against both extremes in the population

Favors genetic phenotypes near the mean

There is no change in the average value of the trait in the population, and the genetic variation in the population is reduced

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4
Q

Disruptive Selection

A

Opposite to stabilizing selection

Eliminates phenotypes near the mean and favors extreme phenotypes

The average value of the trait stays the same and the overall variation is maintained or increased.

Potential to get speciation

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5
Q

Balancing Selection

A

Environment varies over time and space

Certain alleles are favored when rare

Genetic variation is maintained or increased

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6
Q

Frequency-Dependent Selection

A

Direction of selection fluctuates -> first selection favors one trait then it favors another

Each trait is advantageous when rare

Maintains two or more traits in a populations

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7
Q

Misconception: Individuals Evolve

A

Misconceptions:
Individuals evolve/change genetically

Correction:
Natural selection acts on individuals
Populations change/evolve

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8
Q

Misconception: Selection acts at a group/species level

A

Misconceptions:
Natural selection promotes survival of species
Individuals act “the the good of the species”

Correction:
Selection promotes survival/reproduction of individuals
Truly altruistic behavior is selected against

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9
Q

Misconception: Evolution is progressive

A

Misconceptions:
Organisms have become “better” over time

Correction:
Tendency towards increased complexity, organization and specialization
But thousands of instances of groups becoming simpler than ancestors

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10
Q

Misconception: Evolution is goal-oriented

A

Misconceptions:
Adaptations evolve because organisms “want” or “need” them

Correction:
Evolution is “blind” – it does not look ahead
The eviornment connot direct the formation of mutation
No planning
Mutations are random

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11
Q

Misconception: Organisms are perfectly adapted to their envoirments

A

Correction: Not all traits are adaptive

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12
Q

Vestigial Structures

A

Structures present in ancestors but not currently adaptive

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13
Q

Developmental holdovers

A

Ex. Rudimentary mammary glands of human males

-Not vestigial because males never had a use for them to begin with

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14
Q

Genetic Constraints

A

Lack of genetic variation
- selection favors most fit variations from what is available

Genetic Correlations
- Selection for one trait causes correlated, non-optimal increased in another trait

Heterozygote advantage

  • cannot “breed true”
  • some individuals will carry homozygous/less fit genotype
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15
Q

Historical Contraints

A

Traits/structures can only evolve from pre-existing ones

may originally have had different structure/function

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16
Q

Trade-Offs

A

Organism must do many different things at once

energy limited

any strategy has positive and negative impacts

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17
Q

Cultural Evolution

A

Learning over the course of a lifetime and passing that knowledge on to future generations

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18
Q

Mutation

A

Any change in the hereditary material of an organism

Mutations occur when there are errors when DNA is copied

Errors occur most in somatic cells and they will die with the individual

If they happen in gametes, they are passed to offspring (or they can be)

Mutation is a random process

Effects of the mutation depends on the enviornment; deleterious mutations in one environment may be beneficial in another

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19
Q

Deleterious Mutation

A

Cause changes in structure, function, or behavior that decrease individual’s chances of surviving and reproducing

Tend to by eliminated by purifying selection

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20
Q

Neutral Mutation

A

neither helps nor harms an individual

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21
Q

Beneficial Mutation

A

Bestows a fitness advantage on an individual

Most of the genotype is already fairly well adapted; the chances are not high that something new/better will arise

Should increase in frequency due to natural selection

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22
Q

Gene Flow (Migration)

A

Movement of alleles from one population to another

Tends to eliminate genetic differences among populations/equalizes allele frequencies

Can increase genetic diversity in small, isolated populations that tend to lose alleles due to genetic drift

Can reduce the fitness of a population by introducing poorly adapted alleles (well adapted to a different environment)

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23
Q

Genetic Drift

A

A random change in allele frequencies over generation, brought about by chance alone

Over time, random changes in allele frequencies leads tot he fixation of one allele, and the loss of another

All due to chance; occur in all populations, more rapid in small ones

Loss of genetic diversity

Random effect on fitness; allele frequency changes are not adaptive

Effective evolutionary force in small populations; insignificant in large populations

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24
Q

Bottlenecks

A

A sudden constriction in population size

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25
Genetic Bottleneck
a reduction in diversity resulting from the sudden reduction in a large population
26
Founder Event
The establishment of a new population from a small group of individuals
27
Founder Effect
A change in allele frequencies that often occurs when a new population is established Allele frequencies of founder may not be the same as those of the original population Genetic drift is likely Selection pressure in new habitat is likely different
28
Inbreeding
matings between relatives Form of nonrandom mating Hard to avoid in small, isolated populations Causes homozygosity Does not change allele frequencies -> does not cause evolution
29
Inbreeding Depression
Loss of fitness that takes place when homozygosity increases Many recessive alleles -- loss-of-function mutations - little to no effect in heterozygous form, but deleterious/fatal in homozygous Many genes involved in fighting disease occur in heterozygous form
30
Self-Incompatability
Among plants; a form of avoidance to inbreeding
31
Inbreeding as an Indirect cause of Evolution
Inbreeding can "unmask" deleterious recessives by combining them in homozygous form Increases the rate at which natural selection can eliminate these from the population
32
Theoretical Paradox of Sex
Since asexual individuals son't have to produce male offspring, their progeny can produce twice as many grand-offpring
33
Purifying Selection Hypothesis
Asexual individuals have no option but to transmit all deleterious alleles to all offspring Sexual individuals likely to have offspring that lack deleterious alleles present in parents
34
Improved Resistance to Disease Hypothesis
Sexual reproduction generates genetically diverse offspring better able to fight off disease-causing agents like bacteria, viruses, and parasites
35
Sexual Dimorphisms
A difference between the make and the female in a species
36
Sexual Selection
Selection for traits that enhance an individuals ability to obtain a mate Form of natural selection Form of nonrandom mating
37
The Theory of Sexual Selection
Fundamental Asymmetry of Sex "Eggs are expensive, sperm are cheap" Females typically invest must more time and energy into producing and caring for offspring than do males
38
Consequences
Females - Females produce relatively few young during lifetime - Reproductive success if limited only be ability to gain resources - not ability to find mates Males - Males can potentially father a huge number of offspring - Reproductive success not limited by resources but by number of females mates
39
Male-Male Competition
Males compete through assessment and fighting So traits are selected that increase their ability to win fights/avoid unnecessary fights
40
Female Choce
1. Resources - Food, nest sites, parental care... 2. Good Genes - Particularly important when males provide nothing else - Evidence that bright male coloration, vigorous and complex songs and dances etc. can be accurate indicators of male nutrition status and resistance to disease
41
Sex Role Reversals
Sometimes males invest more time/energy in offpsring
42
Speciation
The process by which species form Mutation -> exact same mutations unlikely to occur in different locations Drift -> one allele may be lost in one population but not another
43
Species
Evolutionary independent population or group of populations
44
Biological Species Concept
Species -> populations that are reproductively isolated from one another Do not interbreed in nature and fail to produce viable and fertile offspring when matings take place Strength: - clear, logical Weaknesses: - Can't use with fossils or asexual species - Difficult to apply when closely related populations are geographically far apart
45
Prezygotic Barriers
``` Temporal isolation Habitat isolation Behavioral isolation Mechanical isolation Gametic isolation ```
46
Postzygotic Barriers
Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown
47
Prezygotic Isolation
Mechanisms that prevent individuals from different species from mating Difference in when, where, or how individuals mate
48
Postzygotic Isolation
Mechanisms that operate after mating of individuals of two species occurs Hybrid offspring likely to die early, be infertile, or be less fit
49
Morphospecies Concept
Species -> populations that are morphologically distinct Strengths: - Useful for fossils, sexual and asexual organisms Weaknesses: - Subjective. How much distinction is unnecessary? - Cannot differentiate cryptic species
50
Phylogenetic Species Concept
Species -> smallest monophyletic group on an evolutionary tree Strengths: - Used for fossils, sexual and asexual organisms - Objective Weaknesses: - few well-established phylogenies avaliable
51
Allopatric Speciation
Speciation that begins with physical isolation Populations becomes physically separated
52
Dispersal and Colonization
Colonists establish a population in a novel location Founder effect and genetic drift pronounced Selective pressures may differ
53
Vicariance
A new physical barrier splits population into two or more isolated subgroups
54
Sympatric Speciation
Speciation that occurs among populations that live in the same geographic areas No physical barriers Isolation because of preferences for different habitats
55
Polyploidy
Errors in meiosis or mitosis can sometimes generate polyploidy individuals Have extra sets of chromosomes Common in plants Reproductively isolated from wild-types - can self-ferilize or reproduce with like polypoids Speciation is instantaneous
56
Divergence
When population begin to evolve independently ``` More likely if: Area is large Mobility is restricted Population size is small Generation time is short Behavior is sophisticated in mating selection ```
57
Fossil
Any trace left by an organism that lived in the past
58
Intact
Remains preserved intact - no decomposition Spectacular but rare
59
Compression
Deposition materials compress structure into thin, carbon-rich film
60
Cast
Remains not compressed, decompose after buried, hole left fills with dissolved minerals, creating a cast
61
Permineralized
If remains rot extremely slowly, dissolved mineral can gradually infiltrate cells than harden into stone
62
Radiometric Dating
Uses isotope decay in rocks surrounding the fossil. Can determine the absolute age of the rocks, and the fossil Expensive.
63
Relative Dating
General time of when the fossils lived relative to each other. Not absolute. Based on stratigraphy: - Younger rocks are deposited on older rocks. - Lavas and sedimentary rocks are originally laid down horizontally - Rocks that intrude into seams or cracks are younger than the host rock
64
Habitat Bias
Burial in sediments critical to fossilization Organisms in depositional habitats are more likely to fossilize, as are burrowing organisms
65
Taxonomic and Tissue Bias
Slow decay essential to fossilization Organisms with hard parts (shells, bones) are more likely to fossilize
66
Temporal Bias
Recent fossils are more common than ancient ones Older rocks (and therefore fossils) are destroyed through erosion and tectonic plate movement - Earth's crust recycles itself
67
Abundance Bias
Fossilization improbably Record weighed toward species that are abundant, widespread and on Earth for long periods of time
68
Benefits of Fossil Record
Only way scientists have of examining physical appearance of long-extinct forms and inferring how, where and when they lived
69
Adaptive Radiation
When single lineage diversifies into many descendant species that use a wide variety of habitats and resources
70
Ecological Opportunity
Avaliability of new types of resources Frequently occurs when habitats are unoccupied by competitors (the dominant one either dies or a founder event occurs)
71
Morphological Innovation
Evolution of a key morophological trait that allows descendants to live in new areas, exploit new resources of food or move in new ways
72
Background Extinction
Lower, average rate of extinction observed over the entire history of life
73
Mass Extinction
The rapid extinction of a large number of lineages scattered throughout the tree of life Thus far, 5 mass extinction events we can trace
74
Phylogeny
the evolutionary history of a group of organisms
75
Phylogentic tree
A graphical summary of the evolutionary history of a group of organisms
76
Ancestral Traits
Possessed by an ancestor
77
Derived Traits
Not present in ancestor
78
Monophyletic group
An ancestral population and all its descendants
79
Synapomorphies
A trait unique to a monophyletic group
80
Homology
Similarity in form or structure due to inheritance from common ancestor
81
Homoplasy
Similarities in function or structure due to reasons other than common ancestry Similar traits evolved independently
82
Convergent Evolution
Independent evolution of similar phenotypes in unrelated organisms due to natural selection favoring same characteristics in similar environments
83
Parsimony
Most likely pattern is one that represents the smallest number of changes/least complexity
84
Branches
Species/group through time
85
Nodes/Forks
Ancestral group splits into two or more descendant groups
86
Tips
Group living today or a dead-end/extinction
87
Root
Most ancient node of a tree/common ancestor
88
Taxon
Any named group of organisms
89
Sister Taxa
Groups that occupy adjacent branches
90
Monophyletic group/Clade/Lineage
Includes all the descendants of a particular ancestor and no other
91
Outgroup
Lineage related to organisms of interest but splits off earlier

Biology 180 (5 decks)

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