Ecology Exam 3 (Chapters 22-23) Flashcards
(284 cards)
1
Q
A new era of biology began in 1859 when ____ published ____
A
Charles Darwin published The Origin of Species
2
Q
The Origin of Species focused biologists’ attention on the great ____ of organisms
A
diversity
3
Q
Darwin noted that current species are descendants of ____ species
A
ancestral
4
Q
Evolution can be viewed as both a ____ and a ____
A
pattern, process
5
Q
how can evolution be defined
A
descent with modification
6
Q
what are the two types of evolution
A
marco and micro
7
Q
what did Jean-Baptiste de Lamarck hypothesize about how species evolve
A
that species evolve through use and disuse of body parts and the inheritance of acquired characteristics
8
Q
what is an example of Jean-Baptiste de Lamarck’s hypothesis of species evolution
A
a giraffe stretches is neck and so its offspring will have longer necks
9
Q
when did Darwin travel around the world on the HMS Beagle
A
1831-1836
10
Q
when was the Origin of Species published
A
1859
11
Q
The Greek philosopher Aristotle viewed species as ____ and arranged them on a ____
A
fixed, scala naturae
12
Q
What is Carolus Linnaeus the founder of
A
taxonomy, naming of species
13
Q
what is taxonomy
A
the branch of biology concerned with classifying organisms
14
Q
The study of ____ helped to lay the groundwork for Darwin’s ideas
A
fossils
15
Q
what layer of the earth are fossils found in
A
the strata
16
Q
what is Paleontology
A
the study of fossils
17
Q
why did Darwin consider the fossil record to be highly unreliable
A
-Many places on the earth had not been prospected for fossils.
-Only some types of organisms form well preserved fossils.
-More species have lived than have been discovered as fossils.
-Fossilization is a difficult process, so the fossil record will be full of holes.
-Because organisms migrate, you will not get a continuous record of fossilized species in a single location.
18
Q
The fossil record is one of the direct lines of evidence to support the ____
A
evolutionary theory
19
Q
should the fossils found in the youngest or oldest layers of rock look more like the organisms that exist today
A
youngest
20
Q
what does each layer of sedimentary rock represent
A
a period of geologic time
21
Q
once a species goes extinct will it reappear in the fossil record
A
no
22
Q
what are transitional fossils
A
are fossils that appear to be transitional forms between two distinct large taxa
23
Q
what is an example of a transitional fossil
A
Archaeopteryx siemensii
24
Q
what idea formed from Darwin’s ideas in social and political arenas
A
Social Darwinism
25
what did Social Darwinism argue
the unfit” of human society should be eliminated for the good of the human race
26
what is another name for Social Darwinism
Eugenics
27
what was eugenics used to validate
validate racism, and mistreatment of the impoverished and mentally ill.
28
____ by ____ explains the adaptations of organisms and the unity and diversity of life
descent with modification by natural selection
29
what did Darwin note about the fossils that he found
fossils resembled living species from the area in which they were found
30
he noted that living species ____ other species from areas nearby
resembled
31
Darwin hypothesized that species from the mainland ____ and then ____ on the islands
colonized, diversified
32
what are adaptations
are inherited characteristics that enhance an organism’s survival and reproduction in specific environments
33
what has given rise to the diversity of life
descent with modification
34
what is natural selection
is a process in which individuals with certain inherited traits tend to survive and reproduce at higher rates because of those traits
35
species accumulate differences from their ancestors as they adapt to different ____ over many generations
environments
36
Darwin proposed ____ as an explanation for adaptation
natural selection
37
In reassessing his observations, Darwin perceived adaptation to the ____ and the origin of ____ as closely related processes
environment, new species
38
what is the mechanism of descent with modification
natural selection
39
what are Darwin's three broad observations from the Origin of Species
-The unity of life
-The diversity of life
-The ways organisms are suited to life in their environments
40
The phrase ____ summarized Darwin’s perception of the unity of life
descent with modification
41
True/False. Darwin used the word evolution in his book the Origin of Species
False
42
what is the Darwinian view of the history of life
the history of life is like a tree with branches representing life’s diversity
43
how are large morphological gaps between related groups explained
by the branching process and past extinction events
44
what is artificial selection
humans have modified other species by selecting and breeding individuals with desired traits
45
what were Darwin's two observations
1. Members of a population often vary in their inherited traits
2. All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce
46
what did Thomas Malthus note
the potential for the human population to increase faster than food supplies and other resources
47
if individuals with advantageous heritable traits produce more offspring that survive to reproduce, how will this affect the frequency of this trait
the trait will increase in frequency in the next generation
48
what two Inferences did Darwin make
1. Individuals that are well suited
to their environment tend to leave more
offspring than other individuals.
2. Over time, favorable traits
accumulate in the population
49
what are the key features of natural selection
-Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals
-Natural selection increases the frequency of adaptations that are favorable in a given environment
50
If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to ____
new species
51
Individuals ____ evolve; ____evolve over time
do not, populations
52
Natural selection can only increase or decrease ____ that vary in a population
heritable traits
53
does natural selection create new traits
no, the trait must already be present
54
Adaptations vary with different ____
environments
55
what are the four types of evidence that document the pattern of evolution
1. Direct observations
2. Homology (DNA evidence)
3. The fossil record
4. Biogeography
56
what two examples provide evidence for natural selection
-natural selection in response to introduced species
-the evolution of drug-resistant bacteria
57
what is an example of natural selection in response to introduced species
-Soapberry bugs use their “beak” to feed on seeds within fruits
-Feeding is most effective when beak length is closely matched to seed depth within the fruit
58
in southern Florida, soapberry bugs feed on the native balloon vine with larger fruit; this leads to ____
longer beaks
59
In central Florida, they feed on the introduced goldenrain tree with smaller fruit; this leads to ____
shorter beaks
60
what is an example of evolution of drug-resistant bacteria
-Resistance to penicillin evolved in S. aureus by 1945, two years after it was first widely used
-Resistance to methicillin evolved in S. aureus by 1961, two years after it was first widely used
-When exposed to methicillin, MRSA strains are more likely to survive and reproduce than nonresistant S. aureus strains
-MRSA strains are now resistant to many antibiotics
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Natural selection does not create ____ traits, but ____ or ____ for traits already present in the population
new, edits or selects
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Evolution by natural selection can occur rapidly in species with ____ generation times
short
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the current, local ____ determines which traits will be selected for or selected against in any specific population
environment
64
what is homology
similarity resulting from common ancestry
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what are homologous structures
are anatomical resemblances that represent variations on a structural theme present in a common ancestor
66
what are examples of homologous structures
the bones in the forelimbs of humans, cats, whales, bats
67
Comparative ____ reveals anatomical homologies ____ in adult organisms
embryology, not visible
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what is an example of comparative embryology
all vertebrate embryos have a post-anal tail and pharyngeal arches
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what are vestigial structures
are remnants of features that served a function in the organism’s ancestors
70
what are examples of homologies at the molecular level
are genes shared among organisms inherited from a common ancestor
71
what are evolutionary trees
are diagrams that reflect hypotheses about the relationships among different groups
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Homologies form ____ patterns in evolutionary trees
nested
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Evolutionary trees can be made using different types of data, for example, ____ and ____ data
anatomical and DNA sequence
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what is convergent evolution
is the evolution of similar, or analogous, features in distantly related groups
75
Analogous traits arise when groups ____ to similar environments in similar ways
independently adpat
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what is an example of convergent evolution
types of wings, birds vs. bats
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what does the fossil record provide evidence for
-the extinction of species
-the origin of new groups
-and changes within groups over time
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Fossils can document important ____
transitions
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what is biogeography
the scientific study of the geographic distribution of species, provides evidence of evolution
80
what was Pangaea
Earth’s continents were formerly united in a single large continent
81
what is the term for continents drifting apart
continental drift
82
what does a understanding of continent movement and modern distribution of species allow us to predict
when and where different groups evolved
83
what is evidence that points to the existence of Pangaea
The distribution of fossils across the continents
84
what are endemic species
are species that are not found anywhere else in the world
85
Islands have many endemic species that are often closely related to species on the nearest ____ or ____
mainland or island
86
what is genomics the study of
of whole sets of genes and their interactions
87
what was the goal of the human genome project
is to determine the complete nucleotide sequence of each chromosome
88
how was the human genome project completed
using sequencing machines and the dideoxy chain termination method
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what two approaches were used to obtain the complete sequence
-fragment based mapping & sequencing
-whole-genome shotgun approach
90
The basis of change at the genomic level is ____, which underlies much of genome evolution
mutation
91
____, ____, and ____ of DNA contribute to genome evolution
duplication, rearrangement, and mutation
92
The earliest forms of life likely had only those genes necessary for ____ and ____
survival and reproduction
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The size of genomes has ____ over evolutionary time, with the extra genetic material providing ___ for gene diversification
increased, raw material
94
Accidents in meiosis can lead to one or more ____, a condition known as polyploidy
extra sets of chromosomes
95
what is polyploidy
when you have extra sets of chromosomes
96
The genes in one or more of the extra sets of chromosomes can diverge by ____
accumulating mutations
97
These variations in genes may persist if the organism carrying them ____ and ____
survives and reproduces
98
how many pairs of chromosomes do humans have
23
99
Following the divergence of humans and chimpanzees from a common ancestor, two ancestral chromosomes ____ in the human line
fused
100
Large blocks of genes on human chromosome 16 are found on four ____ chromosomes
mouse
101
when genes are found in both humans and mice what does that indicate for the genes on that block
This indicates that the genes in each block stayed together in both the human and mouse lineages
102
____ are thought to contribute to the generation of new species
chromosomal rearrangements
103
what is the history of chromosomal evolution
-The rate of duplications and inversions seems to have accelerated about 100 million years ago
-This coincides with when large dinosaurs went extinct and mammals diversified
104
what is unequal crossing
over during prophase I of meiosis can result in one chromosome with a deletion and another with a duplication of a particular region
105
____ elements can provide sites for crossover between nonsister chromatids
transposable
106
Also, ____ can occur during ____ so that a part of the template is either skipped, or replicated twice
slippage, DNA replication
107
Evidence suggests that the genes encoding the ____ evolved from one common ancestral globin gene, which duplicated and diverged about 450–500 million years ago
globin proteins
108
After the duplication events, differences between the genes in the globin family arose from the ____ of ____
accumulation of mutations
109
what are the types of globin
hemoglobin (12), myoglobin, cytoglobin, neuroglobin
110
subsequent ____ and random ____ gave rise to the present globin genes, which code for oxygen-binding proteins
duplications, mutations
111
One copy of a ____ can undergo alterations that lead to a completely new ____ for the protein product
duplicated gene, function
112
the lysozyme gene duplicated and evolved into what gene
encodes α-lactalbumin in mammals
113
____ is an enzyme that helps protect animals against bacterial infection
lysozyme
114
α-lactalbumin is a ____ protein that plays a role in milk production in mammals
nonenzymatic
115
Errors in meiosis can result in an exon being ____ on one chromosome and ____ from the homologous chromosome
duplicated, deleted
116
In exon shuffling, errors in meiotic recombination lead to some ____ and ____ of exons, either within a gene or between two nonallelic genes
mixing and matching
117
The current version of the gene for tissue plasminogen activator (TPA) is thought to have arisen by several instances of ____ shuffling and ____ duplication
exon and subsequent
118
transposable elements carry a ____ or groups of ____ to a new position
gene, genes
119
transposable elements create ____ sites for ____ in an RNA transcript
new, alternative splicing
120
Insertion of transposable elements within a regulatory sequence ____ or ____ protein production = regulation
increase or decrease
121
Multiple copies of similar transposable elements facilitate ____, or ____ between different chromosomes
recombination, or crossing over
122
Insertion of transposable elements within a protein-coding sequence may block ____
protein production
123
are changes in the gene sequence usually detrimental or advantageous
detrimental
124
Comparing genome sequences provides clues to ____ and ____
evolution and development
125
Comparisons of genome sequences from different species reveals____
evolutionary history of life
126
Comparative studies of genetic programs that affect ____ development are beginning to clarify the mechanisms that generated the diversity of life-forms present today.
embryonic
127
Genome comparisons of closely related species help shed light on recent ____ events
evolutionary
128
Comparing genomes of very distantly related species helps us understand ____ evolutionary history
ancient
129
Relationships among species can be represented by a____-shaped diagram
tree
130
Highly conserved genes have changed ____ over time
very little
131
what do highly conserved genes clarify between species that diverged from each other long ago
relationships
132
can very ancient genes still be surprisingly similar in disparate species
yes
133
Genomes of closely related species are likely to be organized ____
similarly
134
For example, comparison of the ____ with other ____ gives us clues about what it takes to make a mammal
human genome, mammals
135
Analysis of the ____ and ____ genomes reveals some general differences that underlie the differences between the two organisms
human and chimpanzee
136
do we know how the genetic differences revealed by genome sequencing account for the distinct characteristics of each species
no
137
did genes evolve faster in the human or chimpanzee or the mouse
human
138
what genes evolved faster in humans than chimpanzees or mice
genes involved in defense against malaria and tuberculosis and one that regulates brain size
139
what gene shows evidence of rapid change in the human lineage compared to other primates
FOXP2
140
what might the FOXP2 gene be related to
human speech
141
how many amino acids are only found in the human protein sequence
two
142
what does the mutation of the FOXP2 lead to in humans
severe speech and language impairment in humans
143
when the FOXP2 is removed from mice have the human form of the gene introduced can the mice vocalize
yes, and they are healthy
144
are the mice that have the human FOXP2 have different vocalizations than they did before
yes
145
do humans have high or low within-species genetic variation
low
146
what are the three ways that the human genome can have variations
inversions, deletions and duplications
147
Variation within humans is due to ____
single nucleotide polymorphisms
148
what role do copy-number variants of the human genome play
complex diseases and disorders
149
____, ____, and other ____ are useful genetic markers for studying human evolution
Copy-number variants, SNPs, and other polymorphisms
150
what are SNPS
inversions, deletions, and duplications
151
what genome has the highest genetic diversity
african
152
what does is suggest when a population has higher genetic diversity
the population has been evolving longer
153
Evolutionary developmental biology, or evo-devo, compares ____ processes of different multicellular organisms
developmental
154
Genomic information shows that ____ differences in gene sequence or regulation can result in striking ____ in form
minor, differences
155
what is a homeobox
a 180-nucleotide sequence contained within a gene
156
what are homeotic genes in animals called
Hox genes
157
The ____ is the part of the protein that binds to the DNA, where the protein functions as a transcription factor
homeodomain
158
In addition to homeotic genes, many other developmental genes are highly ____ from species to species
conserved
159
Sometimes small changes in ____ of certain genes lead to major changes in body form
regulatory sequences
160
For example, variation in Hox gene expression controls ____ in leg-bearing segments of crustaceans and insects
variation
161
In other cases, genes with conserved sequences play ____ in different species
different roles
162
True/False do individual organisms evolve
False
163
Natural selection acts on ____, but only ____ evolve
individuals, populations
164
what is microevolution
is a change in allele frequencies within a population over generations
165
what is an allele
alternative form of a gene
166
what are the three main mechanisms that cause allele frequency change
-Natural selection
-Genetic drift
-Gene flow
167
Only ____ consistently causes adaptive evolution
natural selection
168
____ makes evolution possible
genetic variation
169
____ in heritable traits is a prerequisite for evolution by ____
variation, natural selection
170
whose work provided evidence of discrete heritable units (genes)
Gregor Mendel
171
what causes genetic varitation
differences in genes or other DNA segments
172
____ is the product of inherited genotype and environmental influences
Phenotype
173
Natural selection can only act on variation with a ____ component
genetic
174
Some phenotypic differences are determined by a ____ and can be classified on an “either-or” basis
single gene
175
Other phenotypic differences are determined by the influence of two or more genes and vary along a ____ within a population
continuum
176
are phenotypic differences determined by one gene or more than one
it can be either
177
what is it called when a phenotypic difference is determined by two or more genes
multigenic traits
178
what are three examples of multigenic traits
-height
-weight
-skin color
179
Genetic variation can be measured as ____ variability or ____ variability
gene or nucleotide
180
for gene variability, average heterozygosity measures what
the average percent of loci that are heterozygous in a population
181
Nucleotide variability is measured by comparing the ____ of two or more individuals
DNA sequences
182
Nucleotide variation rarely results in ____ variation
phenotypic
183
where do most differences in nucleotide variation occur
noncoding regions (introns)
184
what do variations that occur in coding regions (exons) rarely change
the amino acid sequence of the encoded protein
185
Some phenotypic variation does not result from genetic differences among individuals, but rather from ____ influences
environmental
186
Only genetically determined variation can have ____ consequences
evolutionary
187
New genes and alleles can arise by ____ or ____
mutation or gene duplication
188
Sexual reproduction can result in genetic variation by ____ existing alleles
recombining
189
how do you get new genes
crossing over between two transposons
190
what do new alleles arise from
New alleles arise by mutation, a change in the nucleotide sequence of DNA
191
what is a point mutation
is a change in a single nucleotide in a DNA sequence
192
Only mutations in cells that produce ____ can be passed to offspring
gametes
193
Mutations that alter the phenotype are often ____
harmful
194
Harmful mutations can be hidden from selection in ____
recessive alleles
195
are mutations that results in a change in phenotype ever beneficial
rarely
196
Point mutations in noncoding regions generally result in ____
neutral variation
197
what is neutral variation
conferring no selective advantage or disadvantage
198
when can mutations to genes be neutral
redundancy in the genetic code
199
Chromosomal mutations that ____, ____, or ____ many loci are typically harmful
delete, disrupt, or rearrange
200
Duplication of small pieces of DNA increases ____ and is usually ____ harmful
genome size, less
201
can duplicated genes take on new functions by further mutation
yes
202
Mutation rates are ____ in animals and plants
low
203
Mutation rates are often lower in ____
prokaryotes
204
short generation times allow mutations to accumulate ____
rapidly
205
____ have both high mutation rates and short generation times
Viruses
206
In organisms that reproduce sexually, most genetic variation results from ____ of alleles
recombination
207
what are the three mechanisms that sexual reproduction can shuffle existing alleles into new combinations
-crossing over,
-independent assortment
-fertilization
208
what is the Hardy-Weinberg equation used to test for
whether a population is evolving
209
____ is required for a population to evolve
Genetic variation
210
does genetic variation guarantee that a population will evolve
no
211
____ or ____ factors that cause evolution must be at work for a population to evolve
One or more
212
A ____ is a localized group of individuals capable of interbreeding and producing fertile offspring
population
213
individuals typically only breed with members of their ____ population
own
214
what does a gene pool consist of
consists of all the alleles for all loci in a population
215
A locus is ____ if all individuals in a population are ____ for the same allele
fixed, homozygous
216
If there are two or more alleles for a locus, diploid individuals may be either ____ or ____
homozygous, heterozygous
217
what is the condition to sustain a population with H-W equilibrium
allele and genotype frequencies remain constant from generation to generation
218
Hardy-Weinberg equilibrium describes the constant frequency of _____ in such a gene pool
alleles
219
does the Hardy-Weinburg approach describe a population that is not evolving
yes
220
what are the conditions of the Hardy-Weinburg Equilibrium
-no mutations
-random mating
-no natural selection
-extremely large population size
-no gene flow
221
The Hardy-Weinberg equation can be used to test whether ____ is occurring in a population
evolution
222
The Hardy-Weinburg equation is also used to determine the percentage of a population carrying a ____
specific allele
223
what is the consequence if the condition of "no mutations" for H-W isn't upheld
The gene pool is modified if mutation occur or if the entire genes are deleted or duplicated
224
what is the consequence if the condition of "random mating" for H-W isn't upheld
if individuals mate within a subset of the population, such as near neighbors or close relatives (inbreeding), random mixing of gametes does not occur and genotype frequencies change
225
what is the consequence if the condition of "no natural selection" for H-W isn't upheld
allele frequencies change when individuals with different genotypes show consistent differences in their survival or reproductive success
226
what is the consequence if the condition of "extremely large population size" for H-W isn't upheld
in small populations, allele frequencies fluctuate by chance over time (a process called genetic drift)
227
what is the consequence if the condition of "no gene flow" for H-W isn't upheld
by moving alleles into or out of populations, gene flow can alter allele frequencies
228
what are the three major factors that alter allele frequencies and bring about the most evolutionary change
-natural selection
-genetic drift
-genetic flow
229
what is fitness
reproductive success
230
If ____ is taking place, it results in alleles being passed to the next generation in ____ that differ from those in the present generation
selection, proportions
231
Natural selection ____ cause adaptive evolution
can
232
what is adaptive evolution
a process in which traits that enhance survival or reproduction increase in frequency over time.
233
what does genetic drift describe
describes how allele frequencies fluctuate unpredictably from one generation to the next
234
The ____ a sample (or the ____ the population), the ____ the chance of random deviation from a predicted result
smaller, smaller, greater
235
how does genetic drift reduce genetic variation
random loss of alleles
236
what are the two types of genetic drift
-founder effect
-bottleneck effect
237
how does the founder effect occur
when a few individuals become isolated from a larger population
238
Allele frequencies in the ____ population can be different from those in the larger parent population
small founder
239
when does the bottleneck effect occur
when there is a drastic reduction in population size due to a sudden change in the environment
240
what is the effect of the bottleneck effect
The resulting gene pool may no longer be reflective of the original population’s gene pool
241
If the population remains ____, it may be further affected by genetic drift
small
242
discuss the Case Study: Impact of Genetic Drift on the Greater Prairie Chicken
-Loss of prairie habitat caused a severe reduction in the population of greater prairie chickens in Illinois
-The surviving birds had low levels of genetic variation, and only 50% of their eggs hatched
-Researchers used DNA from museum specimens to compare genetic variation in the population before and after the bottleneck
-The results showed a loss of alleles at several loci
-Researchers introduced greater prairie chickens from populations in other states and were successful in introducing new alleles and increasing the egg hatch rate to 90%
243
list the four effects of genetic drift
-Genetic drift is significant in small populations
-Genetic drift can cause allele frequencies to change at random
-Genetic drift can lead to a loss of genetic variation within populations (founder or bottleneck effects)
-Genetic drift can cause harmful alleles to become fixed
244
what does gene flow consist of
the movement of alleles among populations
245
how can alleles be transferred
through the movement of fertile individuals or gametes
246
Gene flow tends to ____ variation among populations over time (but not always)
reduce
247
Gene flow can affect ____ to local environments
adaptation
248
Gene flow can ____ the fitness of a population
increase
249
what is an example of gene flow increasing the fitness of a population
resistance to insecticides
250
____ is an important agent of evolutionary change in modern human populations
Gene flow
251
Natural selection is the only mechanism that consistently causes ____ evolution
adaptive
252
Evolution by natural selection involves both ____ and ____
chance, sorting
253
New genetic variations arise by ____
chance
254
Beneficial alleles are ____ and favored by natural selection
sorted
255
Only ____ consistently increases the frequencies of alleles that provide reproductive advantage
natural selection
256
Natural selection brings about adaptive evolution by acting on an organism’s ____
phenotype
257
what is relative fitness
is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals
258
Selection favors certain ____ by acting on the ____ of individuals
genotypes, phenotypes
259
what are the three modes of selection
-directional
-disruptive
-stabilizing
260
what does directional selection favor
individuals at one extreme end of the phenotypic range
261
what does disruptive selection favor
individuals at both extremes of the phenotypic range
262
what does stabilizing selection favor
favors intermediate variants and acts against extreme phenotypes
263
Natural selection increases the frequencies of ____ that enhance ____ and ____
alleles, survival, reproduction
264
____ evolution occurs as the degree to which a species is well suited for life in its environment improves
adaptive
265
Because the environment can change, adaptive evolution is a ____ process
continuous
266
Genetic drift and gene flow do not consistently ____ the frequency of alleles that enhance survival and reproduction
increase
267
Both genetic drift and gene flow may ____ or ____ the frequency of beneficial alleles in a population
increase or decrease
268
what is sexual selection
is a process in which individuals with certain inherited characteristics are more likely to acquire mates than other individuals of the same sex
269
what can sexual selection result in
sexual dimorphism
270
what is sexual dimorphism
marked differences between the sexes in secondary sexual characteristics
271
what is intrasexual selection
is direct competition among individuals of one sex (often males) for mates of the opposite sex
272
what is intersexual selection
often called mate choice, occurs when individuals of one sex (often females) are choosy in selecting their mates
273
Showiness of male appearance can ____ a male’s chances of attracting a female while ____ his chances of survival
increase, decreasing
274
which type of sexual selection has males being brightly colored
intersexual selection
275
how does diploidy maintain genetic variation
in the form of recessive alleles hidden from selection in heterozygotes
276
when does balancing selection occur
when natural selection maintains stable frequencies of two or more phenotypic forms in a population
277
what does balancing selection include
-Frequency-dependent selection
-Heterozygote advantage
278
In frequency-dependent selection, the fitness of a phenotype depends on ____ it is in the population
how common
279
what is an example of frequency-dependent selection
right-mouthed and left-mouthed scale eating fish
280
when does heterozygote advantage occur
when heterozygotes have a higher fitness than both homozygotes
281
Natural selection will tend to maintain ____ or ____ alleles at that locus
two or more
282
Heterozygote advantage can result from ____ or ____ selection
stabilizing or directional
283
what is an example of a heterozygote advantage
sickle cell anemia
284
list the four reasons why natural selection cannot fashion perfect organisms
-Selection can act only on existing variations
-Evolution is limited by historical constraints
-Adaptations are often compromises
-Chance, natural selection, and the environment interact
