Download Lecture 6: Adaptation and Evolution

Adaptation
Lecture 6:
Adaptation and Evolution
Pages 180-183
Pages 314-324
Evolution
• _______ change
in a population
• Many different
mechanisms of change
• Ecology affects evolution and evolution affects
ecology
The phenotype is the
expression of the genotype.
• The phenotype is the outward expression of the
genotype manifested in structure and function:
– the genotype is a set of __________________
– the phenotype is the expression of the genotype as
modified by environmental conditions affecting growth
and development
• An evolutionary solution and a genetically
determined characteristic that improves an
organism’s ability to survive in a particular
environment.
Genotype vs Phenotype
• _________________ = genetic make-up of
the individual being measured.
• _________________ = visible manifestation
of a character in an organism
• Variation in plants and animals are a result of
both genetics and environmental factors.
Adaptation results from
natural selection
• Genotype is the unique genetic constitution of
an individual.
• Evolution is any change in the genetic
makeup of a population.
• _____________________________results in
evolutionary change when genetic factors
cause differences in fecundity
and survival among
individuals.
• ________is the reproductive
success of an individual.
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Genetic Terms
• Each chromosome carries units of heredity
called_________________
• The position a gene occupies on a
chromosome = locus
• Genes occupying the same locus on a pair
of chromosomes are called alleles
Genes and alleles
• Genes encode proteins:
– used as part of an organism’s
structure
– may function as enzymes or
hormones
• Different forms of a particular gene
are called _____________________:
– alleles may cause perceptible and measurable
differences in the phenotype (e.g., eye color)
– defective alleles may cause genetic disorders:
Allelic Diversity in Individuals
• Each diploid individual has two copies of
each allele:
– a __________________ individual has two
different alleles
– a __________________ individual has identical
alleles
– alleles may be:
• dominant (expressed in heterozygous individual)
• recessive (masked by dominant allele)
• codominant (result in intermediate phenotype in
heterozygotes)
– most deleterious alleles are recessive
Gene pool
• Basic evolutionary unit is the population
• The total of all the genes in a population is
the “__________________________”
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The Hardy-Weinberg Law
In 1908, Hardy and Weinberg independently
described this fundamental law: the frequencies
of both alleles and genotypes will remain
constant from generation to generation in a
population with:
1.
2.
3.
4.
5.
a large number of individuals
random mating
no _______________
no ________________
no migration between populations
Hardy-Weinberg equation
A1 occurs with a frequency of 0.7 (70%)
A2 occurs with a frequency of 0.3 (30%)
• 0.7+ 0.3 = 1
• Therefore
• A1 A1 : (0.72 = 0.49)
• A2 A2 : (0.32 = 0.09)
• A1 A2 : (2 x 0.7 x 0.3 = 0.42)
• 0.49 + 0.09 + 0.42 = 1
Hardy-Weinberg equilibrium
• Gene A has 2 alleles A1 (p) and A2 (q)
• p + q =1 and (q=1-p) (p=1-q)
Genotype
A1 A1
A1 A2
A2 A2
Freqency
p2
2pq
q2
p2 + 2pq + q2 = 1 the proportions of all the
genotypes in the population add up to 1
• Now, consider random mating in a
population with …
the allele frequencies (p (A) = 0.4 and q(a)
= 0.6)
• Then using simple binomial probabilities we
get
P2 + 2pq + q2 = 1.0 or in our case,
0.16 + 0.48 + 0.36 = 1.0
(AA) (Aa) (aa)
Consequences of HardyWeinberg Law
A population in
HardyWeinberg
equilibrium
does not
____________
(no genetic
change over
time) if the
random union
of gametes
continues
Figure 16.4
• No evolutionary change occurs through the
process of _____________ reproduction
itself.
• Changes in allele and genotype frequencies
can result only from __________________
on the gene pool of a species.
• Understanding the nature of these forces is
one of the goals of evolutionary biology.
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Conditions and violations of the HardyWeinberg Equation
Condition for HardyWeinberg equilibrium
Large population
Corresponding
Mechanism of Evolution
if violated
Genetic drift
No net immigration or
Gene flow
emigration of alleles
No differential mortality or Natural selection
survival by genotype
No new mutations
Mutation pressure
Gene flow
• Emigration and immigration between
populations can result in changes in
allele frequencies or composition if the
movement of alleles is
____________________________
Evolution by natural selection
1. Inherited variation exists for any
character.
– Phenotypic variation often reflects genotypic
variation
2. Resources are limited →
________________
3. Points 1 and 2 above results in individuals
with a better genotype → more resources
→ more offspring than others in
population
Mechanisms of Evolution
• ____________________ – stochastic
(random) shifts in allele frequencies
– typically occurs in small populations
– chance events play a larger role in small
populations but can occur in larger populations
Natural selection
• If allele frequencies remain in HardyWeinberg equilibrium THEN no differential
mortality or reproduction associated with a
given genotype
• Differential representations of genotypes in
future generations resulting from heritable
differences due to survival or reproduction
- ______________________________
Fitness
• Fitness = relative genetic contribution of an
individual’s descendants to future
generations
• __________________________ = expected
number of offspring by a particular genotype
• Relative fitness = relative representation of
a genotype in the next generation
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Sexual Selection
Important properties of fitness
1. Fitness is a property of a____________,
not of an individual or a population.
2. Fitness is specific to a particular
_______________________.
3. Fitness is measured over one generation
or more.
• Some of an organism’s features are
important in attracting ____________
• Sexual selection = selection by one sex for
specific characteristics in individuals of the
opposite sex, usually exercised through
______________________ behaviour….or
• natural selection where fitness of one sex
(often males) depends on their appeal to
the other sex
Kin Selection
The peacock has an elaborate, brightly coloured tail
• A form of genetic selection in which alleles differ in
their rate of propagation because they influence the
___________________ of kin who carry the same
alleles
3 components
• Altruistic behaviour
• __________________ fitness
• Coefficient of relationship
Inclusive fitness: Coefficient of relationship (the fraction of your
genome shared with relatives from your common ancestors)
Proportion shared
Self
full sibling
half sibling
father
mother
offspring
grandparents
niece/nephew
uncle/aunt
first cousin
100%
50%
25%
50%
50%
50%
25%
25%
25%
12.5%
White fronted bee eaters in Kenya provide help at the nest.
These birds are colonial nesters. Helpers tend to aid close
relatives more frequently than distant relatives or unrelated
birds.
Breeders
coeff. of relatedness
father x mother
0.5
father x stepmother
0.25
mother x stepfather
0.25
son x nonrelative
0.25
uncle x nonrelative
0.125
grandmother x nonrelative 0.125
% cases
44.8
9.8
9.2
10.3
1.1
0.6
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Evolution of interactions among
species
• __________________ = physical
resemblance of 2 species resulting from
advantages of similar appearance
2 parts:
• Mimic = the imitative species
• Model = the species the mimic resembles
3 fundamental types of mimicry
1. _____________mimicry: a benign species
resembles a noxious or dangerous one.
2. Müllerian mimicry: several noxious species
come to resemble each other
•
Bees, Wasps (and Ants) - The Order
Hymenoptera
venomous coral snake
Sinaloan milk snake
3. ______________mimicry: a noxious or
dangerous species comes to resemble a
benign one.
Zone-tailed hawk
Turkey vulture
Useful Conclusions from
Population Genetics Studies
• Every population harbors some genetic
_______________ that influences fitness.
• Changes in selective factors in the
environment are usually met by evolutionary
responses.
• Rapid environmental changes caused by
humans will often exceed the capacity of a
population to _________________________ ;
the consequence is extinction.
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