1. AP Bio: Wednesday, 4/4/12 Mini-Unit: MicroEvolution
Homework:
Get started on PS 17.
Do Now:
Take out last night’s HW so you have it handy
What do you think is the difference between macroevolution and microevolution?
What does evolution have to do with genetics?
Today’s Goals:
Explain the difference between macro and microevolution
Apply the Hardy-Weinberg equations to analyzing gene pools in populations
Describe microevolutionary forces that cause changes in gene pools over time

2. EVOLUTION

3. Macroevolution –
One species can branch into two or more species
All life on earth is descended from common ancestors
Microevolution –
Changes in the heritable characteristics in a population over time (population genetics)

4. Populations Genetics (Microevolution)
Are populations evolving? How? Why?

5. Some definitions… Species – Population – Gene pool –
a group of organisms with similar characteristics and genetics that can reproduce and make fertile offspring
Population –
a group of organisms of the same species that live in a given area
Gene pool –
the collection of all the genes (and alleles) in a population
Allele frequency –
the proportion of one allele in the gene pool

6. Example:
In cats, black hair is dominant over white hair. (B = black, b = white)
Imagine a population of 500 cats:
320 are homozygous dominant
160 are heterozygous
20 are homozygous recessive
How many alleles are in the gene pool for this gene?
What is the frequency of the B allele?

7. Hardy-Weinberg Theorem of Genetic Equilibrium
In a non-evolving population, frequencies of alleles and genotypes should remain constant across generations.

8. Hardy-Weinberg equations
Allele frequencies:
p = freq. A allele q = freq. a allele
By definition: p + q = 1
Genotype frequencies:
Freq. of AA genotype =
Freq. of Aa genotype =
Freq. of aa genotype =
Prediction under HW equilibrium:
p2 + 2pq + q2 = 1 p2
pq + qp =
2pq q2

9. Use HW to do two things: Calculate allele frequencies
figure jpg
Use HW to do two things:
Calculate allele frequencies
(given genotype freq’s)
Predict genotype frequencies
(given allele freq’s)

10. Populations Genetics Are populations evolving? How? Why?
H-W equations let us answer a specific aspect of this question:
Are gene (allele) and/or genotype frequencies changing over time?

11. So what? If ACTUAL genotype frequencies match predictions, then…
the population is in HW equilibrium
allele and genotype freq. constant across generations (no evolution)
If ACTUAL genotype frequencies differ from predictions, then…
population is not in HW equilibrium
some evolutionary force is acting!

12. Requirements for Hardy-Weinberg Equilibrium
No natural selection (due to limited resources, etc.)
No mutation
Random mating
No immigration or emigration (no gene flow)
Large population size

13. Evolutionary forces that violate Hardy-Weinberg:
mutation
migration
non-random mating
genetic drift
selection
How does each affect genetic variation within populations?

14. Mutation – transformation of one allele into another
generates genetic variation
alone, not a strong evolutionary force
provides the “raw material” of genetic variation on which selection and drift can act

15. Migration – movement of individuals between populations
“gene flow” between gene pools
maintains genetic variation within populations by bringing in new alleles
prevents populations from genetically diverging (and eventually becoming separate species)

16. Non-random mating
does not change allele freq’s
DOES change genotype freq’s
Assortative mating – individuals prefer mates with same genotype
increases homozygosity at a particular locus
Disassortative – individuals prefer mates with different genotypes
increases heterozygosity at a particular locus

17. Inbreeding – mating between close relatives
increases homozygosity across the genome
danger: “inbreeding depression”
inbred populations often show decreased fitness (due to greater risk of homozygous recessive disorders)

18. (Freeman & Herron 2001)

19. AP Bio: Thursday 4/5/12 Hardy-Weinberg Problems & The Mating Game
Homework:
Lab 8 Analysis Questions
Do Now: Do some math!
Imagine a population of 1,000 fruit flies:
510 have gray bodies (wild-type, dominant)
490 have black bodies (recessive)
What is the frequency of the recessive genotype?
What is the frequency of the recessive allele?
What is the frequency of the dominant allele?
How many flies would you predict to be…
Homozygous dominant?
Heterozygous?

20. Evolutionary forces that violate Hardy-Weinberg:
mutation
migration
non-random mating
genetic drift
selection

21. Genetic drift – random changes in allele frequencies between generations
due to sampling error
greatest effect in small populations
population bottlenecks
founder effect

22. Genetic drift via population bottleneck or founder effect

23. Simulation: Genetic drift at one locus

24. Selection – differential survival and reproduction
Selection – differential survival and reproduction of individuals with different genotypes
Non-random process (unlike genetic drift)
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.

25. Simulation: Selection at one locus

26. AP Bio: Thursday 4/5/12 Hardy-Weinberg Problems & The Mating Game
Homework:
Lab 8 Analysis Questions
Today’s Goals:
Use H-W equations to calculate allele and genotype frequencies
Explain how genetic drift and natural selection affect microevolution
Simulate population genetics and calculate allele and genotype frequencies in “The Mating Game”

27. AP Bio: Wednesday, 4/11/12 Natural Selection & Sexual Selection
Homework:
Due Friday: PS 17 and Lab 8
We will also have a short practice quiz on Friday – based on the problem set
Do Now:
Take out Lab 8 and turn to Part B
Get 2 sample papers and lick them. See if one tastes bad.
Today’s Goals:
Calculate allele and genotype frequencies for a REAL trait in our class (Part B)
Describe various effects of natural selection and sexual selection on the range of traits in a population.

28. Selection – differential survival and reproduction
Selection – differential survival and reproduction of individuals with different genotypes
Non-random process (unlike genetic drift)
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.

30. Classify the following examples as Directional, Stabilizing, or Disruptive Selection:
Human birth weight tends to stay around 7 lbs. (too big = trouble for mom; too small = trouble for newborn)
Many seeds have seed coats of medium thickness (if too thin, no protection; if too thick, germinating seed can’t break through)
Finches need either small beaks (to eat tiny seeds) or large beaks (to crack large seeds).

31. Galapagos finches

33. Balanced Polymorphism (aka Heterozygote Advantage) Ex: sickle cell anemia

34. Frequency-dependent selection

35. Sexual Selection
Peacock Experiments

36. Sexual Selection
Intrasexual – Members of one sex (usually male) compete for access to the other sex
Ex: Sea lions, rams
Intersexual – Members of one sex (usually female) choose certain members of the opposite sex over others
Ex: Pea hens choosing pea cocks