Ecology
Lake Tahoe Community College
Fall qtr
Instructor: Sue Kloss
______________________________________________________________________________________________________________________
Chapter 4 - Population Genetics and Evolution
______________________________________________________________________________________________
I. Intro
A. genetic variation is necessary in a population for natural selection
1. natural selection requirements
2. Over time, natural selection in action causes evolution
3. Genetic info is stored in DNA in the nucleus of eukaryotic cells
4. DNA makeup
5. genetic info storage
6. DNA is the code
7. codon
8. codons specifies a specific amino acid
9. protein recipe
B. The source of genetic variation is mutation and recombination
1. common forms of mutation
2. the new protein
3. altered proteins may or may not be beneficial
4. Mutations are more likely to be beneficial when?
7. Mutation is random
C. Mutation Rates
1. the rate of mutation is very low
2. low rate x the number of nucleotides in a gene (hundreds or thousands)- each org has mutations
3. the more genes for a particular trait, the more likely mutation
D. Recombination
1. independent assortment.
2. crossing over occurs in meiosis
3. Recombination
4. recombination – produce genetic variation very rapidly
5. the new combinations of genetic traits
E. gene pool of a population
1. When are all combinations of different alleles possible in a population
2. many of these combinations are not present in the population at any given time
3. the more varied the gene pool of a species, in general, the more tools a species has to adapt to
changing environmental conditions (evolve).
G. Hardy-Weinberg law
1. Alleles and genotypes in a population remain constant if certain conditions are true
2. natural selection and evolution
3. Hardy-Weinberg equilibrium
H. Most natural populations deviate from Hardy Weinberg equilibrium
1. mutation
2. small population size
3. nonrandom mating
4. migration - even a very little bit, tends to keep increasing genetic variation
5. natural selection - differential survival/repro
a. stabilizing selection
b. directional selection
c. disruptive selection
I. The genotypes of individuals within a population often vary geographically
1. differences in selective factors or random changes
2. subpopulations divided by a natural barrier like a canyon
3. if natural selection is more of a factor than gene flow, then subpops have diff in allele frequencies
4. Turesson in the early 1900s, collected seeds from a single species, grew them in common gardens
5. ecotypes - specific adaptations to particular environment
6. clines- gradual change in a trait in response to environmental variation
a. Yarrow (Achillea millefolium) shows ecotypic variation
b. So does Potentilla glandulosa
7. Evolutionary changes in allele frequencies have been documented in natural populations
1
J. Ecologists can learn much from population genetics studies
1. every population has some gv that influences fitness; evolution continues in all populations
2. changes in environmental characteristics will cause natural selection to alter the genotype
frequencies in populations; in other words, populations will change to become more well adapted to the
new environment
3. rapid environmental changes (eg. human induced changes) may happen too rapidly for natural
selection to work, in which case decline of a population to extinction is possible
a. eg exotic introductions of competitors or pests/parasites
Lesson Objectives
1. Does natural selection act on the individual, the population, or the community? How does it act?
2. What are 2 sources of genetic variation in life forms? Describe how variation is produced.
3. Define recombination, and explain how it works in sexual reproduction.
4. Distinguish between a genome and a gene pool.
5. What 5 characteristics must be true for a population to maintain its genetic structure?
6. Why are small populations at risk for losing genetic variation? Describe 3 types of events that may cause loss of
genetic variation in a small population.
7. Define an ecotype. Define a cline. Describe the type of experiment that will distinguish between the two conditions.
8. Distinguish between stabilizing, disruptive and directional selection.
9. Describe one case of natural selection that has been documented.
2