1. When Allele Frequencies Stay the Same..
Chapter 12
When Allele Frequencies Stay the Same..

2. Gene Pool Population Genetics
Branch of genetics that considers not individuals or families, but ALL of the alleles in a population.
Gene Pool

3. Gene Flow

4. 12.1 Importance of Knowing Allele Frequencies
Frequencies can be calculated for alleles, genotypes, or phenotypes.

5. Phenotypic Frequencies
Determined empirically (observing how common a condition is in a population).
Data supplied to genetic counselors

6. Frequencies change when any of the following occur:
Shifting allele frequencies in populations provide the small steps of genetic change = microevolution
Frequencies change when any of the following occur:
Nonrandom Mating
Migration of individuals
Reproductively isolated subgroups form within a larger population
Mutation occurs
Natural Selection

7. Hardy-Weinbery Equilibrium
Hardy says, “I am reluctant to intrude in a discussion concerning matters of which I have no expert knowledge, and I should have expected the very simple point which I wish to make to have been familiar to biologists.”
He was hearing biologist assume that dominant traits will tend to increase in populations, while recessive traits will become rarer

8. The famous equation… p² + 2pq + q² = 1.0
P² = homozygous dominant individuals
2pq = heterozygous individuals
q² = homozygous recessive individuals
The idea is that if the proportion of genotypes remains the same from gen to gen, then that gene is not evolving!

9. It’s rare but it is seen…
Rare for protein encoding genes that affect phentoype.
Occurs in repeated sequences that do NOT affect phenotypes – therefore not acted upon by Natural Selection

10. Solving Hardy Weinberg Equilibrium
Within a population, the easiest to value to determine is q².
q² q p p² pq
Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on an exam, calculate the five variables:

11. Practical Application of Hardy-Weinberg Equilibrium
Truly determining risk for a couple.
What are the chances my child will have cystic fibrosis?
Known: Cystic fibrosis affects 1 in 2,000 Caucasians!
2pq!
1/2000 = q² q p

12. .043 1 ??

13. 1 1 1 4 23 23
Why?!?

14. 12.4 – DNA Fingerprinting – A practical test of Hardy Weinberg Assumptions
Polymorphism – a site on a chromosome that varies within at least 1% of the population
Can be as small as one nucleotide (Snp)
The ability to distinguish people based upon polymorphisms = basis of DNA Fingerprints
Restriction Enzymes
Spots polymorphisms

15. DNA Fingerprinting and Hardy Weinberg
Variations of a gene are caused by altered proteins
Different Proteins = Different Sizes
Different sizes travel different lengths

17. If the frequency of +/+ (p²) = 1/3,000 then a DNA fingerprint will run multiple genes of known statistics!

18. What are the chances another person did it??

19. Changing Allele Frequencies
Chapter 13
Changing Allele Frequencies

20. Nonrandom Mating
Surveys show we marry people similar to ourselves 80% of the time.
Worldwide, 1/3 of all marriages occur between people who were born fewer than 10 miles apart
Prize bull can fertilize thousands of cows
Chinese Immigrant to South Africa – 7 wives (he had a dominant disorder – teeth fall out)
356 living descendents
70 have the dental disorder

21. Nonrandom Mating
1 in 200 Hopi Indians are albino. How can the culture of Indians cause the trait to be so prevalent?
Mutation can cause individuals to be resistant to HIV.
How would this mutation cause a change in Hardy Weinberg equilibrium over time?
Would you expect blood type frequencies to be in Hardy Weinberg equilibrium? Why or why not?

22. Nonrandom Mating
How can “Cystic Fibrosis Summer Camps” be a detriment to Hardy Weinberg equilibrium?
In a very religious Jewish sect in New York City, marriages are NOT permitted between carriers of the same inherited disease
Arranged marriages AFTER genetic testing
How does a consanguineous population affect the equilibrium?
Population of Sardinia (island near Italy) – 86% of the individuals have the same X chromosome.

23. Migration How can allele frequencies tell a story of the past?
LOCATION
PREVALENCE OF Galactokinase deficiency
Bulgaria
1:1600
Austria
1:153,000
Germany
1:157,000
France
1:2,200,000

24. Allele frequencies that vary between neighboring populations = Cline
Geographical Clues
Allele frequencies that vary between neighboring populations = Cline
Cline gradients can be gradual
Steep gradients often are a result of geographical barriers
Evidence: The fertile lands along the Nile River
Mummies

25. Linguistic Clues Italy
Is the changing frequencies due to geography or language?
Blood groups study across the region of Italy
Language groups were more closely related than Geography based.

26. Small Population
Genetic Drift – the random chance of alleles being passed on to the next generation

27. Founder Effect
When a small population leaves another and starts a new colony. The new colony will develop a different allele frequency than the original.

28. Pennsylvania is a breeding ground…
Germantown and The Dunkers
Lancaster County Amish
11 different disorders are more prevalent amongst the Amish compared to the US population
Population
Blood Type
U.S
Dunker
European A
40%
60%
45% B
15% 5%
Rh-
11%

29. Haplotypes
Haplotype – a group of VERY tightly linked genes on a chromosome
Genetic drift leads to common diseases amongst populations but also other genes that are close to that locus.

30. Population Bottleneck

31. Mutation
Many mutations in homozygous forms are lethal, but since they can be hidden in heterozygous the allele can be passed on.
Genetic Load – the collection of deleterious alleles in a population.

32. Natural Selection and Heterozygote Advantage