1. Option D:
Evolution
D4: The Hardy-
Weinberg
Principle

2. Population Genetics = Foundation for studying evolution
D 4.1 Explain how the Hardy-Weinberg equation is derived.
Population Genetics = Foundation for studying evolution
Darwin’s could not explain how inherited variations are maintained in populations - not “trait blending”
A few years after Darwin’s “Origin of Species”, Gregor Mendel proposed his hypothesis of inheritance: Parents pass on discrete heritable units (genes) that retain their identities in offspring

3. Hardy-Weinberg Theorem:
D 4.1 Explain how the Hardy-Weinberg equation is derived.
Hardy-Weinberg Theorem:
Frequencies of alleles & genotypes in a population’s gene pool remain constant from generation to generation unless acted upon by agents other than sexual recombination (gene shuffling in meiosis)
Equilibrium = allele and genotype frequencies remain constant

4. Hardy-Weinberg Theorem:
D 4.1 Explain how the Hardy-Weinberg equation is derived.
Hardy-Weinberg Theorem:
Hypothetical, non-evolving population
preserves allele frequencies
Serves as a model (null hypothesis)
natural populations rarely in H-W equilibrium
useful model to measure if forces are acting on a population
measuring evolutionary change
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

5. Hardy-Weinberg theorem
D 4.1 Explain how the Hardy-Weinberg equation is derived.
Hardy-Weinberg theorem
Counting Alleles
assume 2 alleles = B, b
frequency of dominant allele (B) = p
frequency of recessive allele (b) = q
frequencies must add to 1 (100%), so:
p + q = 1 BB Bb bb

6. Hardy-Weinberg theoremBB Bb bb
D 4.1 Explain how the Hardy-Weinberg equation is derived.
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:
p2 + 2pq + q2 = 1

7. Hardy-Weinberg theorem
D 4.1 Explain how the Hardy-Weinberg equation is derived.
Hardy-Weinberg theorem
Alleles: p + q = 1
Individuals: p2 + 2pq + q2 = 1 B b BB Bb bb BB Bb bb

8. q2 (bb): 16/100 = .16 q (b): √.16 = 0.4 p (B): 1 - 0.4 = 0.6
D 4.2 Calculate allele, genotype and phenotype frequencies for two alleles of a gene, using the Hardy-Weinberg equation.
population: 100 cats
84 black, 16 white
How many of each genotype?
q2 (bb): 16/100 = .16
q (b): √.16 = 0.4
p (B): = 0.6
p2=.36
2pq=.48
q2=.16 BB Bb bb
Must assume population is in H-W equilibrium!
What are the genotype frequencies?

9. Assuming H-W equilibrium
D 4.2 Calculate allele, genotype and phenotype frequencies for two alleles of a gene, using the Hardy-Weinberg equation.
p2=.36
2pq=.48
q2=.16
Assuming H-W equilibrium BB Bb bb
Null hypothesis
p2=.20
p2=.74
2pq=.64
2pq=.10
q2=.16
q2=.16
Sampled data 1:
Hybrids are in some way weaker.
Immigration in from an external population that is predomiantly homozygous B
Non-random mating... white cats tend to mate with white cats and black cats tend to mate with black cats.
Sampled data 2:
Heterozygote advantage.
What’s preventing this population from being in equilibrium. bb Bb BB
Sampled data
How do you explain the data?
How do you explain the data?

10. to verify that the PRESENT population is in genetic equilibrium
D 4.2 Calculate allele, genotype and phenotype frequencies for two alleles of a gene, using the Hardy-Weinberg equation.
Using the calculated gene frequency to predict the EXPECTED genotypic frequencies in the NEXT generation OR
to verify that the PRESENT population is in genetic equilibrium

11. Assuming all the individuals mate randomly
D 4.2 Calculate allele, genotype and phenotype frequencies for two alleles of a gene, using the Hardy-Weinberg equation.
Assuming all the individuals mate randomly
SPERMS B A
B 0.43
A 0.57
EGGS AA AB
p*p= p2
p*q AB BB
q*q= q2
p*q

12. Close enough for us to assume genetic equilibrium
D 4.2 Calculate allele, genotype and phenotype frequencies for two alleles of a gene, using the Hardy-Weinberg equation.
Close enough for us to assume genetic
equilibrium
Genotypes
Expected frequencies
Observed frequencies AA
p2 = 0.32
233  747 = 0.31 AB
2pq =0.50
385  747 = 0.52 BB
q2 =0.18
129  747 = 0.17

13. Application of H-W principle
Sickle cell anemia
inherit a mutation in gene coding for hemoglobin
oxygen-carrying blood protein
recessive allele = HsHs
normal allele = Hb
low oxygen levels causes RBC to sickle
breakdown of RBC
clogging small blood vessels
damage to organs
often lethal

14. Sickle cell frequency High frequency of heterozygotes
1 in 5 in Central Africans = HbHs
unusual for allele with severe detrimental effects in homozygotes
1 in 100 = HsHs
usually die before reproductive age
Sickle Cell:
In tropical Africa, where malaria is common, the sickle-cell allele is both an advantage & disadvantage. Reduces infection by malaria parasite.
Cystic fibrosis:
Cystic fibrosis carriers are thought to be more resistant to cholera:
1:25, or 4% of Caucasians are carriers Cc
Why is the Hs allele maintained at such high levels in African populations?
Suggests some selective advantage of being heterozygous…

15. Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells
Malaria 1 2 3

16. Heterozygote Advantage
In tropical Africa, where malaria is common:
homozygous dominant (normal)
die or reduced reproduction from malaria: HbHb
homozygous recessive
die or reduced reproduction from sickle cell anemia: HsHs
heterozygote carriers are relatively free of both: HbHs
survive & reproduce more, more common in population
Hypothesis:
In malaria-infected cells, the O2 level is lowered enough to cause sickling which kills the cell & destroys the parasite.
Frequency of sickle cell allele & distribution of malaria

17. Conditions for Hardy-Weinberg Equilibrium:
D 4.3 State the assumptions made when the Hardy-Weinberg equation is used.
Conditions for Hardy-Weinberg Equilibrium:
Hardy-Weinberg Theorem describes a non-evolving
population.
Extremely large population size (no genetic drift).
No gene flow (isolation from other populations).
No mutations.
Random mating (no sexual selection).
No natural selection.

18. D 4.3 State the assumptions made when the Hardy-Weinberg equation is used.
If any of the Hardy-Weinberg conditions are not met  microevolution occurs
Microevolution = generation to generation change in a population’s allele frequencies

19. Main Causes of Microevolution
Mutation
Gene Flow
Non-random mating
Genetic Drift
Selection

20. Not every mutation has a visible effect.
1. Mutation & Variation
Mutation creates variation
new mutations are constantly appearing
Mutation changes DNA sequence
changes amino acid sequence?
changes protein?
changes structure?
changes function?
changes in protein may change phenotype & therefore change fitness
Every individual has hundreds of mutations
1 in 100,000 bases copied
3 billion bases in human genome
But most happen in introns, spacers, junk of various kind
Not every mutation has a visible effect.
Some effects on subtle.
May just affect rate of expression of a gene.

21. 2. Gene Flow Movement of individuals & alleles in & out of populations
seed & pollen distribution by wind & insect
migration of animals
sub-populations may have different allele frequencies
causes genetic mixing across regions
reduce differences between populations

22. Human evolution today Are we moving towards a blended world?
Gene flow in human populations is increasing today
transferring alleles between populations
Are we moving towards a blended world?

23. 3. Non-random mating
Sexual selection

24. 4. Genetic drift Effect of chance events founder effect bottleneck
small group splinters off & starts a new colony
bottleneck
some factor (disaster) reduces population to small number & then population recovers & expands again
Warbler
finch
Tree finches
Ground finches
1 family has a lot of children & grandchildren therefore has a greater impact on the genes in the population than other families
Genghis Khan tracked through Y chromosome.

25. Founder effect
When a new population is started by only a few individuals
some rare alleles may be at high frequency; others may be missing
skew the gene pool of new population
human populations that started from small group of colonists
example: colonization of New World
Small founder group, less genetic diversity than Africans
All white people around the world are descended from a small group of ancestors
100,000 years ago
(Chinese are white people!)

26. Bottleneck effect
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

27. Cheetahs All cheetahs share a small number of alleles 2 bottlenecks
less than 1% diversity
as if all cheetahs are identical twins
2 bottlenecks
10,000 years ago
Ice Age
last 100 years
poaching & loss of habitat

28. Conservation issues
Peregrine Falcon
Bottlenecking is an important concept in conservation biology of endangered species
loss of alleles from gene pool
reduces variation
reduces adaptability
Breeding programs must consciously outcross
Golden Lion Tamarin

29. 5. Natural selection
Differential survival & reproduction due to changing environmental conditions
climate change
food source availability
predators, parasites, diseases
toxins
combinations of alleles that provide “fitness” increase in the population
adaptive evolutionary change