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Next Lab IV: Student-Driven Project 1
Complete Homework 6 at home:
Correlation/Regression
Bring 3 abstracts to trade with group + TA
Complete SDP1 Proposal Worksheet 1
Use pg. 109-114
Next lecture:
Ch 10: Life Histories and Evolution
The hierarchical nature and processes of
different levels of ecological systems:
• Individual organism: How do structure, physiology,
and behavior lead to the individual’s survival and
reproduction?
•
Population: What determines the number of
individuals and their variation in time and space?
• Community: What determines the diversity and
relative abundance of organisms living together?
• Ecosystem: How do energy and matter move in the
biotic and abiotic environment?
• Biosphere: How do air, water, and the energy and
chemicals they contain circulate globally?
Today: Ch 16: Population Genetics
Population Ecology
Genetics Evolution
Darwin’s finches…
Objectives
• Define (micro)evolution and its relation to genetics
• Sources of genetic variation
• Forces causing change in gene frequency in pop
Small population size
Assortative mating
Gene flow
Natural selection
• Which force(s) maintain vs. eliminate genetic
variation?
Which force is strongest in plants? animals?
***Sample exam question.
A species of scale insects extracts fluids from
branches of pine trees. They have very limited
movement. In an experiment, these insects were
transplanted 1) between branches of the same pine
tree, and 2) from one pine tree to another pine tree
of the same size.
1.
2.
3.
4.
5.
State the hypothesis/prediction that was being
tested as an “If…then…”
Summarize the results in one concise sentence.
Do the results support the hypothesis?
Predict whether gene flow or natural selection would be
a more powerful force affecting the genetic structure of
this insect. Explain your choice.
Predict whether the genetic makeup of populations of the
insect on adjacent trees would be homogeneous or
differentiated. Explain your choice.
Genetic structure (differentiation) of
populations is determined by ecological
factors, e.g. heavy metals from mines.
*** A ‘pre-test’ on adaptation, natural
selection, evolution, fitness…
Non-Curesistant
Copper from mine in soil
of plant subpopulation
Cu-resistant
individuals
TIME
*** What is definition of (micro)evolution?
Change in allele frequency in a
population through time…
***What must be present for natural
selection to cause evolutionary change?
Genetic variation
***What is the ultimate source of genetic
variation?
Mutation, a change in nucleotide in DNA
---> change in amino acid it specifies
---> change in phenotype of organism
• A change in just one nucleotide can have
phenotypic effects.
Genetic variation revealed via
electrophoresis
What do different patterns of coloration
(different phenotypes) represent in the
population?
***How much genetic variation exists?
***Why is genetic variation important?
• In changing environments, the reservoir
of genetic variation may take on positive
survival value.
• Rapid environmental change by humans
may exceed the capacity of a population
to respond by evolution --> extinction
***Are most mutations beneficial? Are
most mutations dominant? What
happens to harmful mutations?
• Most mutations are harmful and recessive; natural
selection weeds out most deleterious genes, leaving only
those that suit organisms to their environments.
• Mutations are likely to be beneficial when the relationship
of the organism to its environment changes.
• Selection for beneficial mutations is the basis for
evolutionary change, enabling organisms to exploit new
environmental conditions.
Genetic variation is also produced by
chromosome recombination during 1)meiosis
and by 2) fertilization.
How does sexual reproduction rapidly
produce new combinations of genes-->
abundant variation for natural selection to
work on?
• Crossing over
during
meiosis…
• Random new
combinations
from
fertilization
The gene pool represents the total
genetic variation in the population =
genotypes (alleles) of all individuals.
• ***Does evolutionary change occur through
sexual reproduction itself?
Hardy-Weinberg Equilibrium:
Gene pool: generation 1: p = .8
q = .2
Hardy-Weinberg equilibrium: frequencies
of alleles and genotypes stay constant
through time…unless additional forces
operate.
Sexual
reproduction
Gene pool: generation 2: p = .8
q = .2
***Does evolutionary change occur
through sexual reproduction itself?
• No (Hardy-Weinberg Law).
• Changes in allele and genotype frequencies
(= evolution) can result only from additional
forces acting on the gene pool of a species.
• Understanding the nature of these forces
and their relative importance is one goal of
evolutionary biology.
***What forces can cause change in genotype
frequency?
1) Effects of small population size
a) Genetic drift
b) Founder effect
c) Population bottlenecks
2) Assortative (non-random) mating
3) Gene flow (= dispersal/migration) -->
homogenizes subpopulations
4) Natural selection --> differentiates
subpopulations
Genetic drift:
5 of 10 plants
leave offspring
Generation 1 Generation 2
p = .5, q = .5
2 of 10 plants
leave offspring
Generation 3p
p = 1.0, q = 0
Change in allele frequency due to random variation in
births and deaths.
p =.7, q =.5
Population Bottleneck: period of small pop. size.
…subject to genetic drift