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I. What is evolution? Review.
A. Change over time.
Evolution occurs in a punctuated equilibrium that includes gradual changes (due to natural selection) and rapid changes (due to stochastic factors).
1. Natural Selection : The mechanism for gradual evolution.
1. Variation, 2. Selection, 3. Reproduction
2. Stochastic Factors
Random events effect the outcome of evolution (often cause rapid changes). These include droughts, volcanic eruptions, etc. These lead to… genetic drift . Genetic drift is the change in genetic makeup of a population caused by stochastic factors and isolation. It is more noticeable in small populations.
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I. What is evolution? Review.
B. When a new species evolves, speciation has occurred.
On the Galapagos, 1 finch species (the “founding fathers and mothers”) evolved into 13 different species. This speciation was due to isolation (allopatric speciation). New species can also evolve due to selection and competition (sympatric speciation).
It is called Adaptive radiation or divergent evolution when many species evolve from one species.
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II. Measuring Evolution
A. Simulations
Data generated by models simulating selection, reproduction and stochastic factors demonstrate evolution.
The Effect of Stochastic Factors on the Number of Variations Remaining in the Final Populuation
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Mainl and Isl and Ne ar/La rge
Island Distance/Size
Isl and Far/Sm all
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II. Measuring Evolution
B. Phenotypic/ physical measurements
See the Grant’s work with
Galapagos Finches:
Generational data shows natural selection and stochastic factors lead to evolution.
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II. Measuring Evolution
C. Allele frequencies
1. Hardy and Weinberg argued that if five conditions are met, a population's allele (number of A’s [p] and a’s [q]) and genotype frequency will remain constant from generation to generation
(and, consequently, no evolutionary change would occur).
This balance is known as Hardy-Weinberg equilibrium.
Basically, the Hardy-Weinberg equation describes the status quo.
If the five conditions are met, then no change (no evolution) will occur in either allele or genotype frequencies in the population.
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II. Measuring Evolution
C. Allele frequencies
2. The Hardy-Weinberg Mathematical Formula
• If ‘A’ and ‘a’ are alleles for a particular gene and each individual has two alleles, then p represents the frequency of the A (dominant) allele
• If ‘A’ and ‘a’ are alleles for a particular gene and each individual has two alleles, then q represents the frequency of the a (recessive) allele
• p + q = 1
Always. So when p changes, so must q and vice versa. AND, if p or q changes over time, evolution has occurred .
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II. Measuring Evolution
C. Allele frequencies
3. The conditions of Hardy-Weinberg equilibrium are as follows:
1. Large population
2. Random mating
3. No mutation
4. No migration
5. No selection
If all conditions are met, NO EVOLUTION occurs. (Since all of this seldom happens, evolution often does occur).
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II. Measuring Evolution
C. Allele frequencies
4. Summary
Population of Organisms
Unique Gene Pool
Hardy-Weinberg conditions are met:
• no mutation
• no migration
But wait!
One or more Hardy-Weinberg conditions are NOT met:
• large population size
How does all the genetics stuff work?
• no natural selection
Allele Frequencies do
NOT change
Allele Frequencies change
Genetic Equilibrium Genetic Disequilibrium
Evolution will NOT occur Evolution will occur
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A. Raw material for evolution (and, so, a way to measure evolution).
-How variation created (mutation)
-How selected traits passed on (reproduction)
-How change can be measured (allele frequencies)
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B. How it works
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B. How it works
2. Background: meiosis
R r u u
Z Z
P p t t
H h
6 genes (12 alleles)
4 chromosomes (2 pairs)
Meiosis summary example: how gametes form
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Only half of alleles present in each cell. These cells can combine with other gametes to form the new cell
(zygote) of a new organism.
MEIOSIS:
Sex cells duplicate and divide twice to form daughter cells.
R u
Z
P t
H r u
Z p t h
R u
Z
P t
H r u
Z p t h
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B. How it works
3. Simple: Punnet squares
Possible alleles from female gamete
(egg)
Possible alleles from male gamete (sperm)
R r
R r r r r r
Possible offspring
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