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

EVOLUTION

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)

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

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

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?

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

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

Use HW to do two things: Calculate allele frequencies figure 21-07.jpg Use HW to do two things: Calculate allele frequencies (given genotype freq’s) Predict genotype frequencies (given allele freq’s)

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?

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!

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

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

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

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)

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

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)

(Freeman & Herron 2001)

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?

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

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

Genetic drift via population bottleneck or founder effect

Simulation: Genetic drift at one locus http://darwin.eeb.uconn.edu/simulations/drift.html

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.

Simulation: Selection at one locus http://darwin.eeb.uconn.edu/simulations/selection.html

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”

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.

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.

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).

Galapagos finches

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

Frequency-dependent selection

Sexual Selection Peacock Experiments

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