The document discusses Hardy-Weinberg equilibrium, which states that allele and genotype frequencies in a population will remain constant from generation to generation if the population meets certain conditions: large size, random mating, no mutations, migration, drift or selection. It provides an example calculation of genotype frequency. The document also covers genetic variation within and between populations, factors influencing variation like isolation and drift, minimum viable population size, effective population size, and causes of extinction.

1. Hardy-Weinberg equilibrium
 if p = frequency of allele A
q = frequency of allele a
 p + q = 1, ( p + q )2 = 1
 p2 + 2pq + q2 = 1
 if only law of probability affects the
frequency w/ which gametes combine
to form new individuals

2.  Bisexual population
 Large population
 Random mating
 No mutation
 Migration ~ 0
 Natural selection does not affect the
locus

3.  A population that is in Hardy-Weinberg
equilibrium will experience no change
in either genotype frequency or allele
frequency
 If one or more of the conditions is
violated, genotype frequency and allele
frequency will change

4. Example
 If only 6% of the population displays
pale eyes (recessive gene e). What is
the frequency of genotype Ee in this
population?
q2 = 0.06 ---> q = 0.24
p + q = 1 ---> p = 0.76
Ee = 2pq = 2(0.76)(0.24) = 0.36

5. Genetic variation
 Cline – a measurable, gradual change
over a geographical region in the
average of some phenotype character
 Ecotype – abrupt changes in the
phenotype characters within a species,
which often reflect abrupt changes in
local environment

6.  Geographic isolates – semi-isolated
populations prevented by some
extrinsic barriers from a free flow of
genes
 Genetic polymorphism – the existence
within a species or population of
different forms of individuals

7. Maintenance of
balanced polymorphism
(vs. transitional or directional polymorphism)
 heterosis
 diversifying evolution
 frequency-dependent selection
 selective forces operating in different
directions within different patches of a
fine mosaic in the population

8.  Stabilizing, directional, diversifying or
disruptive evolution
 Speciation
 Allopatric speciation
 Sympatric speciation

10. Isolation mechanism
 Pre-zygotic: habitat, temporal,
ethological, mechanical
 Post-zygotic
 hybrid inviability or weakness
 hybrid sterility
 F2 breakdown

11. Reduction in variation
 inbreeding, bottlenecks, founder effect,
genetic drift
 genetic drift - random shifts in allele
frequencies

12. Effect of small populations
 More demographic variation, inbreeding
depression, genetic drift → higher risk of
extinction
Minimum viable population size
 the threshold # of individuals that will
ensure the persistence of subpopulation
in a viable state for a given time interval

13. Effective population size (Ne)
 the size of a genetically idealized
population with which an actual
population can be equated genetically, Ne
= N , if
 equal sex ratio
 equal probability of mating
 constant dispersal rate
 progeny per family randomly distributed

14.  unequal sex ratio
Ne = 4 Nm˙Nf / (Nm + Nf )
 population fluctuation
1 / Ne = (1 / t )(1/N1 + 1/N2 + … + 1/Nt)
 non-random progeny distribution
Nk
Ne = -----------------------------------------
(N/N-1)˙Vk/k˙(1+F) + (1-F)

15. Effect of continental drift
 Distribution/radiation of monotremes
and marsupials

16. Extinction and its causes
 Natural causes: climatic changes and
stochastic event
 Human disturbance
 habitat alteration
 over-exploitation
 exotic species
 diseases and other factors