Transcript PopandGenIntro03

Find this presentation online at http://www.redwood.org/stewart
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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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Number of Variations (Colors)
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Main land
Is land Near/L arge
Is land Dista nce/Size
Is land Far/Small
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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
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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
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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
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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
Population of Organisms
C. Allele frequencies
4. Summary
Unique Gene Pool
Hardy-Weinberg conditions are
met:
• no mutation
• no migration
One or more Hardy-Weinberg
conditions are NOT met:
But wait!
• large population size
How does all the genetics stuff work?
• random mating
• no natural selection
Allele Frequencies do
NOT change
Genetic Equilibrium
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Evolution will NOT occur
Allele Frequencies
change
Genetic Disequilibrium
Evolution will occur
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III. Genetics Review
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)
B. How it works
1. Background: vocab
gene: codes for a trait
allele: form of a gene (A or a)
genotype: genetic make-up (AA, Aa, or aa)
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phenotype: trait
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III. Genetics Review
B. How it works
1. Background: vocab
dominant: A
recessive: a
heterozygous: Aa
homozygous: AA or aa
gamete: reproductive cell (contains half of
alleles)
meiosis: how gametes form
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III. Genetics Review
B. How it works
2. Background: meiosis
R r
u u
Z Z
6 genes (12 alleles)
P p
t t
H h
4 chromosomes (2 pairs)
MEIOSIS:
Sex cells duplicate and
divide twice to form
daughter cells.
Meiosis summary
example:
how gametes form
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.
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P
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III. Genetics Review
Possible alleles from male
gamete (sperm)
B. How it works
3. Simple: Punnet squares
Possible
alleles from
female gamete
(egg)
R r
r
Possible
offspring
R
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r
r
r
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