Lec 11: Genetics II
1. Gregor Mendel (1822-1884)
- Interested in inheritance
- Pea plants: easy to grow + breed, 7 characteristics with discrete traits
- He noted “factors” [genes] were discrete, heritable, produced predictable ratios
- Most phenotypic characters much more complex than Mendel’s pea characteristics.
- X chromosome larger and has more genes than Y
- Assume dominance, X-linked
- Autosomal dominant: at least one parent is affected, every generation
3. Correcting misconceptions about dominant + recessive alleles
- Dominant + recessive alleles equally likely to be passed on, both expressed. Frequency of an allele is
independent of whether it is dominant or recessive.
Lec 12: Population Genetics
- Study of allele frequencies + changes to allele frequencies in populations
- Can predict genotype frequencies from allele frequencies (if not evolving)
- Genotype (C^R C^R), observed (320), HW (p^2), proportion (.8^2), expected (proportion x total of all
- Frequency of alleles. Ex. f(C^R) = p = [2(320) + 160]/3(500). p + q calculated from observed.
- Observed = expected ----> hardy-weinberg equilibrium
- HWE = null model. X^2 < 3.84
Lec 13: Microevolution
- Evolution at the level of alleles
- Evolution = change in allele frequency in a given population over time.
1. Causes of change in allele frequency?
- Natural selection
- Genetic drift
- Gene flow
2. How do new alleles arise in a species?
- Horizontal gene transfer
3. HWE assumptions (not evolving)
- No mutations
- Random mating
- No natural selection
- Large population
- No gene flow
4. 3 modes of natural selection? - Adaptive
- Directional selection (one phenotype more/less fit)
- Disruptive selection (both phenotypic extremes most fit)
- Stabilizing selection (both phenotypic extremes are least fit)
5. What is genetic drift? - Non-adaptive
- Change in allele frequencies due to chance events
- Random, not result of fitness advantages/disadvantages
- Effects strongest in small population that stays small
- Reduces genetic diversity in a population + can fix alleles
- Alleles fixed when it has a frequency of 1.0
6. Special case of genetic drift: Founder effect