Download PHA_Bio9_Evolution Intro09 - "The Biosphere": Biology at PHA

DO NOW: What comes to mind when
you hear the word “EVOLUTION”
HOMEWORK: Complete the “In
your Own Words” Section of the
Hummingbird Activity.
EVOLUTION:
Genetic changes in a
population or species
over time
Micro-Evolution
Small-scale
 Changes in a population’s gene pool over
time
 Caused by natural selection and/or genetic
drift
Example: CF allele becomes more common in
European populations because it protects
against tuberculosis

Macro-Evolution



Large-scale, often over a very long time
Branching of one species into two species
Leads to the idea that all species share a
common ancestor
Example: Evolution of whales from four-legged
land mammals
Micro-evolution leads to Macro-evolution
Some New Evolution Terms

Population


Gene Pool


All the genes and all of their alleles in population
Relative Frequency


Group of individuals from the same species that interbreed
The proportion of one allele in the whole gene pool
Evolution (on a population scale)

Any change in the relative frequency of alleles over time



One allele becomes more common, another becomes less common
Change in a population NOT change in an individual
Fitness

The ability of a particular genotype to reproduce and pass
on its genes to the next generation
Hummingbirds and Evolution


How does evolution really work?
Let’s look at the scientists studying natural
selection in Hummingbird Populations in
Ecuador:
http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html
Selection – differential survival and reproduction
of individuals with different genotypes

Natural selection involves…

More offspring are born than can survive

Competition/struggle for survival for limited resources

Variation between individuals that makes some better
able to survive and reproduce

This variation is heritable/genetic (can be passed on)
Result: Over many generations, the genotypes that are
better able to survive and reproduce become more
common in the population.
Sources of Genetic Variation

Mutations



Any change to a DNA sequence
Rare
Sometimes harmful, sometimes helpful

Mutations to egg or sperm = inheritable
Mutations to body cells = not inheritable (CANCER)

Gene Shuffling


Meiosis divides the genetic info and fertilization
recombines it


23 pairs of chromosomes = 8.4 million different combinations of
genes
Crossing Over during meiosis increases the number of
different combinations of alleles
Galapagos Finch Activity…
Let’s think back: What are the
connections to Sickle Cell Anemia and
Natural Selection?




Recessive Disorder
Result of a single gene mutation in hemoglobin, the
substance that helps blood cells carry oxygen.
Amino acid valine replaces glutamic acid in the
hemoglobin protein, making blood cells sickleshaped.
People who are heterozygous are partially resistant
to malaria (carried by mosquitoes)
Balanced Polymorphism
(a.k.a.: Heterozygote Advantage)
Ex: sickle cell anemia
DO NOW: What is the
difference between polygenic vs.
single gene traits?
HOMEWORK: no homework…
unless you feel like revising the Galapagos
Finch Activity (note: 5% reduction)
Human Inheritance

Single Gene Traits:



Traits controlled by a single gene (A or a)
i.e.: widows peak
Polygenic Traits:



Traits controlled by two or more genes
Often with more than two alleles for gene.
i.e.: skin color, eye color, body shape, height, etc.
Frequencies of Polygenic Traits
3 Modes of Selection for Polygenic
Traits:

Directional Selection
Stabilizing Selection
Disruptive Selection

Remember:




Natural Selection only really acts on the organism
NOT the genes.
It only selects for traits based on whether the
organism dies or lives to reproduce.
Directional Selection
•Individuals with Phenotypes at one
extreme die off or fail to reproduce
•Individuals with Phenotypes at the
other end have greater fitness and
leave a higher number of offspring.
•This shifts the relative frequency in
the direction of the successful
extreme.
When it Happens:
If there is a change in the environment
that favors the phenotype at one
extreme and not the other.
http://www.gwu.edu/~darwin/BiSc150/PopGen/NS.html
Stabilizing Selection

Individuals with
phenotypes at both
extremes die off or fail to
reproduce.

Individuals with
intermediate phenotypes
have better survival.

Results in populations of
individuals with
intermediate phenotypes.
Less variation at the
extremes.
http://www.gwu.edu/~darwin/BiSc150/PopGen/NS.html
Disruptive Selection

Individuals with
phenotypes at both
extremes have better
survival

Individuals with
intermediate
phenotypes die off or
fail to reproduce

Can result in two distinct
phenotypes, which can
lead to subpopulations
http://www.gwu.edu/~darwin/BiSc150/PopGen/NS.html
What kind of selection is this?
Galapagos Finches
Tuesday: 4.28.09
DO NOW:
Log Into Your Computers!
HOMEWORK:
Read Section 16-3 (pgs. 404 – 410)
Finish Analyzing Data Questions (pg. 408 #1-4)
On page 410, answer questions #1-3.
Key Questions:
1. What is the evidence that one species
can branch into two?
2. What is the evidence that multiple
species are evolutionarily related?
Evolution Dry Lab Part A:
Computer Lab: All in the Family:
Which Animals are the Closest Relatives?
Link:
http://www.pbs.org/wgbh/evolution/change/family/index.html
Wednesday: 4.30.09
Title: Species and Speciation
DO NOW:
What do you think a
“species” is?
HOMEWORK:
No HOMEWORK TONIGHT (unless you need to
work on Part A or revise last night’s HW) 
SPECIES
A
group of similar organisms
 Breed with each other
 Produce Viable Offspring
Speciation –
•The formation of new species.
•The gene pools of two populations must become separated
Ex: The Galapogos Finches
Steps of Speciation:
1.
2.
Reproductive Isolation
Changes in the Gene Pool
1. Gene Pools Diverge
2. Genetic Barriers to
Reproduction
I. Reproductive Isolation
One population becomes isolated from the rest of
the species
1.
Behavior:

2.
Geographic



3.
Changes in courtship or other reproductive strategies
Geographic barrier splits population (i.e.: river,
mountain, body of water, etc.)
Populations are separated and cannot interbreed
Conditions of their local environment select certain traits
Temporal

Species reproduce at different times or have other
behavior that becomes time sensitive (i.e.: feeding)
II. Changes in the Gene Pool
1.
2.
Gene Pools Diverge:

The isolated populations become genetically different.

Due to selection and/or genetic drift

Two separate gene pools emerge
Genetic Barriers to Reproduction



The two populations are no longer able to interbreed
Due to genetic differences in habitat preference, mating
behavior, or physical compatibility
Competition may arise between these two new species
They are now two separate species!
Reproductive Barriers That Maintain
Separate Species

Before mating occurs



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Geographic barriers
Ecological/habitat differences
Temporal differences
Behavioral/courtship differences
Mechanical differences
Chemical differences
After mating occurs



Hybrid inviability
Hybrid breakdown
Hybrid sterility
Famous Hybrids
(Less so)… Famous Hybrids

Real-World Research…
Move to “Evidence for Evolution
Presentation”