Population Genetics (Chp. 13-15)
Allele Frequencies- Chp. 13 pp. 263-276
Changing Allele Frequencies- Chp. 14 pp. 277-298
Origins of Evolution- Chp. pp. 15 299-322
Study genetics on different levels (the order that this class has been in)
1.
2.
3.
4.
Biochemical level- Nitrogenous bases, genes, amino acid, protein
Organismal level- individuals of different organisms
Population level- Humans in a certain area/race/country/continents/classroom
Other levels (Human Race)
Chapter 13
Population- any group of members of the same species in a given geographical area at a specific time
Population genetics – a branch that considers all of the alleles in a population which constitute a gene pool
Gene Flow- the movement of alleles due to migration between populations
I.
Importance- use allele frequencies to track genetic variants
a. Microevolution-small steps in genetic change
b. Changes happen when
i. Individuals of one genotype are more likely to produce offspring with each other than
those of other genotypes. (non random mating)
ii. Individuals migrate
iii. Reproductively isolated groups form within larger population (genetic drift)
iv. mutation introduces new alleles into a population
v. People with a particular genotype are more likely to produce viable, fertile offspring
under a specific environmental condition than individuals of other genotypes (natural
selection)
c. Macroevolution-formation of a new species (two individuals of the opposite sex can no longer
reproduce)
d. Hardy-Weinberg equilibrium-frequencies of alleles stays constant (very rare)
i. Hardy - math, Weinberg - geneticist
ii. In order for alleles to stay the same the following must be met.
1. Random Mating2. No migration
3. Mutation does not occur
4. Characteristics of the offspring are not selected against by the environment
5. Population is very large
iii. Equation- (fig. 13.1)
1. p = dominant alleles and q = recessive alleles
2. p + q = 1.0
3. p2 + 2pq + q2 = 1.0
(p2 = homozygous dominant, 2pq = heterozygous, q2 = homozygous recessive)
II.
Practical Applications- in order to use the equation we need to know the frequency of one genotype
(usually the homozygous recessive)
a. Use known incidence of condition in the population to tell people their chances of producing
offspring with different condition
b. X-Linked traits alter this equation
III.
DNA Finger Printing- calculate probabilities that certain genetic variants occur in two places by
chance (fig 13.4 and 13.5)
a. Restriction Enzymes-cut DNA at particular short sequences
b. SNPs (single nucleotide polymorphisms)- create different fragment lengths that can be mapped.
c. Electrophoresis separates fragments of different sizes
d. Population Statistics are used to interpret DNA fingerprint (tracked alleles must fit HardyWeinberg- not protein encoding genes)
Chapter 14
I.
II.
III.
IV.
V.
Nonrandom matinga. Choose mates (can alter Hardy-Weinberg by using a selection coefficient)
b. Disproportionate contribution to the next generation
c. Effective population - the number of individuals that evenly contribute to the gene pool.
i. Ex: Wolves – (effective population does not include all members of pack)
d. Cultural traditions / Inbreeding
i. Can calculate the inbreeding coefficient (F) by manipulating Hardy-Weinberg
ii. Inbreeding  heterozygous genotypes is reduced
iii. The variation in alleles is critical to the survival of a species and allows organisms to
adapt to changing environments.
iv. Heterozygosity- The amount of heterozygous alleles
v. Cheetahs and black-footed ferrets have low heterozygosities meaning they are “fragile”
populations
(2pq –H)__
vi. F =
2pq
Where H = observed heterozygosity (heterozygous genotypes / total # of genotypes)
vii. F ≤ 0 (no inbreeding)
viii. F = 1 (self fertilization)
ix. If F < 0 then heterozygosity increased therefore no inbreeding
x. 2pq ≠ 0 – must have a large effective population size
Migration
a. Tracked using historical, geographical, and Linguistic clues
b. Must be accounted for using modifications to Hardy-Weinberg
i.
q = m │(q – qm)│
1. m = rate of migration (# of migrants ÷ #of natives)
2.
q = change in recessive allele frequency
3. qm = recessive allele frequency of the immigrants
Genetic Drift- changes in gene frequencies because small groups are separated
a. Founder Effect- small groups of people leave their homes
i. Can amplify certain allele frequencies
b. Population Bottleneck- when many members of a group die
i. only a few individuals are left to replenish the population
ii. cheetahs and black-footed ferrets have gone through population bottlenecks resulting in
reduced heterozygosity
Mutation
a. introduces new alleles
Natural Selection- survival rate changed based on phenotypes
a. phenotypes therefore change genotypes and allele frequencies
b. can remove alleles or retain alleles
c. Balanced Polymorphism- retaining “bad” alleles because the heterozygote has an advantage
i. this allows disease-causing alleles to persist
ii. ex: carriers for sickle cell are resistant to malaria
Chapter 15 – Human Origins and Evolution (Covered using a Video and a PowerPoint)
I.
Human Origins
II.
Molecular Evolution
III.
Molecular Clocks- mutation rates used estimate branches within the evolutionary tree