1. Ch. 22/23 Warm-up What is the evidence for evolution?
(Review) What are the 3 ways that sexual reproduction produces genetic diversity?
What is 1 thing you are grateful for today?

2. Ch. 23 Warm-up
In a population of 200 mice, 98 are homozygous dominant for brown coat color (BB), 84 are heterozygous (Bb), and 18 are homozygous (bb).
The allele frequencies of this population are:
B allele: ___ b allele: ___
The genotype frequencies are:
BB: ___ Bb: ___ bb: ___
Use the above info to determine the genotype frequencies of the next generation:
B (p): ___ b (q): ___
BB (p2): ___ Bb (2pq): ___
bb (q2): ___

3. Ch. 23 warm-up
Use the following information to help you answer the question below:
Population = 1000 people
AA = 160 Aa = 480 aa = 360
What are the genotype ratios? Allele frequencies?
Use directional, stabilizing or disruptive selection to answer the following:
The mice in the Arizona desert have either dark or light fur.
Birds produce 4-5 eggs per clutch
Average human baby weighs 7 lbs.
Darwin's finches and beak size during drought

4. The Evolution of Populations
Chapter 23

5. What you must know:
How mutation and sexual reproduction each produce genetic variation.
The conditions for Hardy-Weinberg equilibrium.
How to use the Hardy-Weinburg equation to calculate allelic frequencies and to test whether a population is evolving.

6. Smallest unit of evolution
Microevolution: change in the allele frequencies of a population over generations

7. Darwin did not know how organisms passed traits to offspring
Mendel published his paper on genetics
Mendelian genetics supports Darwin’s theory  Evolution is based on genetic variation

8. Sources of Genetic Variation
Point mutations: changes in one base (eg. sickle cell)
Chromosomal mutations: delete, duplicate, disrupt, rearrange  usually harmful
Sexual recombination: contributes to most of genetic variation in a population
Crossing Over (Meiosis – Prophase I)
Independent Assortment of Chromosomes (during meiosis)
Random Fertilization (sperm + egg)

9. Population genetics: study of how populations change genetically over time
Population: group of individuals that live in the same area and interbreed, producing fertile offspring

10. Gene pool: all of the alleles for all genes in all the members of the population
Diploid species: 2 alleles for a gene (homozygous/heterozygous)
Fixed allele: all members of a population only have 1 allele for a particular trait
The more fixed alleles a population has, the LOWER the species’ diversity

11. Hardy-Weinberg Theorm
Hardy-Weinberg Theorem: The allele and genotype frequencies of a population will remain constant from generation to generation …UNLESS they are acted upon by forces other than Mendelian segregation and recombination of alleles Equilibrium = allele and genotype frequencies remain constant

12. Conditions for Hardy-Weinberg equilibrium
No mutations.
Random mating.
No natural selection.
Extremely large population size.
No gene flow.
If at least one of these conditions is NOT met, then the population is EVOLVING!

13. Hardy-Weinberg Principle
Allele Frequencies:
Gene with 2 alleles : p, q
p = frequency of dominant allele (A) q = frequency of recessive allele (a)
Note:
1 – p = q
1 – q = p
p + q = 1

14. p2 + 2pq + q2 = 1 Hardy-Weinberg Equation Genotypic Frequencies:
3 genotypes (AA, Aa, aa)
p2 = AA (homozygous dominant)
2pq = Aa (heterozygous)
q2 = aa (homozygous recessive)
p2 + 2pq + q2 = 1

15. Allele frequencies

16. Genotypic frequencies

17. Strategies for solving H-W Problems:
If you are given the genotypes (AA, Aa, aa), calculate p and q by adding up the total # of A and a alleles.
If you know phenotypes, then use “aa” to find q2, and then q. (p = 1-q)
To find out if population is evolving, calculate p2 + 2pq + q2.
If in equilibrium, it should = 1.
If it DOES NOT = 1, then the population is evolving!

18. Hardy-weinberg practice problem #1
The scarlet tiger moth has the following genotypes. Calculate the allele and genotype frequencies (%) for a population of 1612 moths.
AA = Aa = 138 aa = 5
Allele Frequencies:
A = a =
Genotypic Frequencies:
AA =
Aa =
aa =

19. Hardy-weinberg practice problem #2: PTC Tasters
Taster = AA or Aa Nontaster = aa
Tasters = ____ Nontasters = ___
q2 = q =
p + q = 1 p = 1 – q =
p2 + 2pq + q2 = 1

20. Causes of evolution

21. Conditions for Hardy-Weinberg equilibrium
No mutations.
Random mating.
No natural selection.
Extremely large population size.
No gene flow.
If at least one of these conditions is NOT met, then the population is EVOLVING!

22. Minor Causes of Evolution:
#1 - Mutations
Rare, very small changes in allele frequencies
#2 - Nonrandom mating
Affect genotypes, but not allele frequencies
Major Causes of Evolution:
Natural selection, genetic drift, gene flow (#3-5)

23. Major Causes of Evolution
#3 – Natural Selection
Individuals with variations better suited to environment pass more alleles to next generation

24. Major Causes of Evolution
#4 – Genetic Drift
Small populations have greater chance of fluctuations in allele frequencies from one generation to another
Examples:
Founder Effect
Bottleneck Effect

25. Genetic Drift

26. Polydactyly in Amish population
Founder Effect
A few individuals isolated from larger population
Certain alleles under/over represented
Polydactyly in Amish population

27. Northern elephant seals hunted nearly to extinction in California
Bottleneck Effect
Sudden change in environment drastically reduces population size
Northern elephant seals hunted nearly to extinction in California

28. Major Causes of Evolution
#5 – Gene Flow
Movement of fertile individuals between populations
Gain/lose alleles
Reduce genetic differences between populations

29. How does natural selection bring about adaptive evolution?

30. Fitness : the contribution an individual makes to the gene pool of the next generation
Natural selection can alter frequency distribution of heritable traits in 3 ways:
Directional selection
Disruptive (diversifying) selection
Stabilizing selection

31. Directional Selection: eg
Directional Selection: eg. larger black bears survive extreme cold better than small ones
Disruptive Selection: eg. small beaks for small seeds; large beaks for large seeds
Stabilizing Selection: eg. narrow range of human birth weight

32. Sexual selection
Form of natural selection – certain individuals more likely to obtain mates
Sexual dimorphism: difference between 2 sexes
Size, color, ornamentation, behavior

33. Sexual selection
Intrasexual – selection within same sex (eg. M compete with other M)
Intersexual – mate choice (eg. F choose showy M)

34. Preserving genetic variation
Diploidy: hide recessive alleles that are less favorable
Heterozygote advantage: greater fitness than homozygotes
eg. Sickle cell disease

35. Natural selection cannot fashion perfect organisms.
Selection can act only on existing variations.
Evolution is limited by historical constraints.
Adaptations are often compromises.
Chance, natural selection, and the environment interact.

36. Sample Problem
Define the following examples as directional, disruptive, or stabilizing selection:
Tiger cubs usually weigh 2-3 lbs. at birth
Butterflies in 2 different colors each represent a species distasteful to birds
Brightly colored birds mate more frequently than drab birds of same species
Fossil evidence of horse size increasing over time