1. Evolution(Natural Selection, Genetic Drift, Hardy-Weinberg)

2. How do genetic variations occur?
What is Evolution?
Change in the genetic makeup of a population over time.
Fitness – ________________________________________________.
Populations can evolve, not individuals.
Diverse gene pool good for long-term survival of a species. Genetic variations are important!
How do genetic variations occur?

3. Where does Variation come from?
Mutations
_______________________
errors in mitosis & meiosis
environmental damage
Sexual reproduction
___________________
genetic recombination
new arrangements of alleles in every offspring
new combinations = new phenotypes

4. Genetic variation in a population

5. Essence of Darwin’s ideas
Natural selection
____________variation exists in populations
____________________
more offspring than the environment can support
__________________
for food, mates, nesting sites, escape predators
differential survival
successful traits = adaptations
adaptations become more common in population

6. Lamarckian vs. Darwinian view
in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring
Darwin
giraffes born with longer necks survive better & leave more offspring who inherit their long necks 

7. Evolution by Natural Selection
Environment is always changing
_______________________of the population
_________________ = a genetic variation favored by natural selection.
When allele frequencies change in a population, the species has evolved
Natural selection is _______________, because those with most fit traits are selected for survival and reproduction “Survival of the Fittest”

8. STABILIZING SELECTION
Effects of Selection
Changes in the average trait of a population
_____________
STABILIZING SELECTION
____________
___________
giraffe neck
horse size
human birth weight
rock pocket mice

10. Heterozygote Advantage
________________________________________
Ex: Sickle Cell Anemia
aa – dies of sickle cell anemia
Aa – some side affects BUT resistant to malaria!
AA – no disease present BUT prone to malaria

11. In addition to natural selection, evolutionary change is also driven by random processes…

12. II. GENETIC DRIFT
The smaller the population, the less genetic variety it has.
In a very small population, alleles can be lost from one generation to the next, simply by random chance.
When a population evolves only because of this type of random sampling error, _______________is taking place.

13. Genetic Drift
Chance events changing frequency of traits in a population
not adaptation to environmental conditions
not selection
_________________
small group splinters off & starts a new colony
it’s random who joins the group
Bottleneck
a disaster reduces population to small number & then population recovers & expands again but from a limited gene pool
____________________________
Founders: When a new population is started by only a small group of individuals. Just by chance some rare alleles may be at high frequency; others may be missing; skew the gene pool of new population. Ex: human populations that started from small group of colonists
example: colonization of New World
Bottleneck: When large population is drastically reduced by a disaster-famine, natural disaster, loss of habitat…loss of variation by chance event
alleles lost from gene pool not due to fitness, narrows the gene pool

14. Ex: Cheetahs 2 bottlenecks
10,000 years ago
Ice Age
last 100 years
poaching & loss of habitat
All cheetahs share a small number of alleles
less than 1% diversity

15. Human Impact on variation
Artificial selection/Inbreeding
Loss of alleles in gene pool
______________________
Reduces adaptability
Overuse of antibiotics/Insecticides
Resistance increased

16. Hardy Weinberg: Population Genetics
Using mathematical approaches to calculate changes in allele frequencies…this is evidence of evolution.

17. Hardy-Weinberg equilibrium
Hypothetical, non-evolving population
preserves allele frequencies
Natural populations are never in H-W equilibrium
useful model to measure if evolution is occurring
G.H. Hardy (the English mathematician) and W. Weinberg (the German physician) independently worked out the mathematical basis of population genetics in Their formula predicts the expected genotype frequencies using the allele frequencies in a diploid Mendelian population. They were concerned with questions like "what happens to the frequencies of alleles in a population over time?" and "would you expect to see alleles disappear or become more frequent over time?"
G.H. Hardy
mathematician
W. Weinberg
physician

18. Evolution of populations
Evolution = change in allele frequencies in a population
hypothetical: what conditions would cause allele frequencies to not change?
____________________(no genetic drift)
no migration (no gene flow in or out)
no mutation (no genetic change)
_________________(no sexual selection)
no _______________(everyone is equally fit)
H-W occurs ONLY in non-evolving populations!

19. Populations & gene pools
Concepts
a population is a localized group of interbreeding individuals
gene pool is _______________in the population
remember difference between alleles & genes!
______________is how common is that allele in the population
how many A vs. a in whole population

20. Hardy-Weinberg theorem
Frequencies are usually written as decimals!
Counting Alleles
assume 2 alleles = B, b
frequency of dominant allele (B) = ___
frequency of recessive allele (b) = ___
frequencies must add to 1 (100%), so:
p + q = 1 BB Bb bb

21. Hardy-Weinberg theorem
Counting Individuals
frequency of homozygous dominant: p x p = p2
frequency of homozygous recessive: q x q = q2
frequency of heterozygotes: (p x q) + (q x p) = 2pq
frequencies of all individuals must add to 1 (100%), so:
________________ BB Bb bb

22. H-W formulas Alleles: _________= 1 Individuals: ____________= 1 B b BB

23. Practice Problem:
In a population of 100 cats, there are 16 white ones. White fur is recessive to black.
What are the frequencies of the genotypes?

24. Tips for Solving HW Problems:
Solve for q first.
Then solve for p.
Don’t assume you can just solve for p2 if only given dominant phenotypic frequency.
READ carefully!!!