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. Biochemical level- Nitrogenous bases, genes, amino acid, protein
  2. Organismal level- individuals of different organisms
  3. Population level- Humans in a certain area/race/country/continents/classroom
  4. 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

  1. Importance- use allele frequencies to track genetic variants
  2. Microevolution-small steps in genetic change
  3. Changes happen when
  4. Individuals of one genotype are more likely to produce offspring with each other than those of other genotypes. (non random mating)
  5. Individuals migrate
  6. Reproductively isolated groups form within larger population (genetic drift)
  7. mutation introduces new alleles into a population
  8. 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)
  9. Macroevolution-formation of a new species (two individuals of the opposite sex can no longer reproduce)
  10. Hardy-Weinberg equilibrium-frequencies of alleles stays constant (very rare)
  11. Hardy - math, Weinberg - geneticist
  12. In order for alleles to stay the same the following must be met.
  13. Random Mating-
  14. No migration
  15. Mutation does not occur
  16. Characteristics of the offspring are not selected against by the environment
  17. Population is very large
  18. Equation- (fig. 13.1)
  19. p = dominant alleles and q = recessive alleles
  20. p + q = 1.0
  21. p2+ 2pq + q2= 1.0

(p2 = homozygous dominant, 2pq = heterozygous, q2 = homozygous recessive)

  1. Practical Applications- in order to use the equation we need to know the frequency of one genotype (usually the homozygous recessive)
  2. Use known incidence of condition in the population to tell people their chances of producing offspring with different condition
  3. X-Linked traits alter this equation
  4. DNA Finger Printing- calculate probabilities that certain genetic variants occur in two places by chance (fig 13.4 and 13.5)
  5. Restriction Enzymes-cut DNA at particular short sequences
  6. SNPs (single nucleotide polymorphisms)- create different fragment lengths that can be mapped.
  7. Electrophoresis separates fragments of different sizes
  8. Population Statistics are used to interpret DNA fingerprint (tracked alleles must fit Hardy-Weinberg- not protein encoding genes)

Chapter 14

  1. Nonrandom mating-
  2. Choose mates (can alter Hardy-Weinberg by using a selection coefficient)
  3. Disproportionate contribution to the next generation
  4. Effective population- the number of individuals that evenly contribute to the gene pool.
  5. Ex: Wolves – (effective population does not include all members of pack)
  6. Cultural traditions / Inbreeding
  7. Can calculate the inbreeding coefficient (F) by manipulating Hardy-Weinberg
  8. Inbreeding  heterozygous genotypes is reduced
  9. The variation in alleles is critical to the survival of a species and allows organisms to adapt to changing environments.
  10. Heterozygosity- The amount of heterozygous alleles
  11. Cheetahs and black-footed ferrets have low heterozygosities meaning they are “fragile” populations

(2pq –H)__

  1. F = 2pq

Where H = observed heterozygosity (heterozygous genotypes / total # of genotypes)

  1. F ≤ 0 (no inbreeding)
  2. F = 1 (self fertilization)
  3. If F < 0 then heterozygosity increased therefore no inbreeding
  4. 2pq ≠ 0 – must have a large effective population size
  1. Migration
  2. Tracked using historical,geographical, and Linguistic clues
  3. Must be accounted for using modifications to Hardy-Weinberg
  4. q = m │(q – qm)│
  5. m = rate of migration (# of migrants ÷ #of natives)
  6. q = change in recessive allele frequency
  7. qm = recessive allele frequency of the immigrants
  8. Genetic Drift- changes in gene frequencies because small groups are separated
  9. Founder Effect- small groups of people leave their homes
  10. Can amplify certain allele frequencies
  11. Population Bottleneck- when many members of a group die
  12. only a few individuals are left to replenish the population
  13. cheetahs and black-footed ferrets have gone through population bottlenecks resulting in reduced heterozygosity
  14. Mutation
  15. introduces new alleles
  16. Natural Selection- survival rate changed based on phenotypes
  17. phenotypes therefore change genotypes and allele frequencies
  18. can remove alleles or retain alleles
  19. Balanced Polymorphism- retaining “bad” alleles because the heterozygote has an advantage
  20. this allows disease-causing alleles to persist
  21. ex: carriers for sickle cell are resistant to malaria

Chapter 15– Human Origins and Evolution (Covered using a Video and a PowerPoint)

  1. Human Origins
  2. Molecular Evolution
  3. Molecular Clocks- mutation rates used estimate branches within the evolutionary tree