Biology 205 Population Genetics

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I. Evolution: Darwin's Dangerous Idea.

A. Define the term evolution as used by biologists today.

• Modification with genealogy. All kinds of organisms linked by having a common ancestor.
• Change in the genetic make up of a population.

B. Explain the meaning significance of the following ideas.

• Evolution is a population process.
• Heritable phenotypic variation is important.

II. Define population genetics.

A. Review the four main subdisciplines of genetics. See page 457

• Distinguish between Population genetics and Quantitative genetics
• Explain the meaning if the phrase: neo-Darwinian Synthesis

B. Define the following basic concepts related to population genetics.

• Mendelian Population = Deme or local freely interbreeding population.
• Gene pool
• Allele frequency, polymorphism

B. Be able to calculate allele frequencies from genotypic frequencies. See p 459-460

In class we do these sorts of calculations using my snapdragon example

III Explain the Hardy Weinberg Law and its significance to population genetics. pp 461 - 464

A. Developed to settle a question- Do dominant alleles become more common through time?

B. State the assumptions of the Hardy Weinberg Law. Note these assumptions are idealizations!

• Effectively infinitely large population
• Random mating
• No mutation
• No migration in or out of the population
• No natural selection

C. Be able to mathematically state and derive the Hardy Weinberg Law of Equilibrium:

Mathematical form of the law. p² + 2pq + q² = 1 where p and q are the allele frequencies for a particular gene locus.

• Expansion of binomial (p + q)² = 1. See Table 22.2
• Can be expanded to situations where there are more than two alleles at a locus.
• Relationships between allele frequencies and genotypic frequencies
• More than two alleles per locus example p 464

D. Use the Hardy Weinberg Law to do the following:

• Explain why dominant alleles do not increase in frequency if Hardy Weinberg assumptions are met
• Calculate the frequency of recessive alleles given the frequency of homozygous recessive individuals in the population.

E. Explain the importance of Hardy Weinberg in population genetics

• Deviations from Hardy Weinberg equilibrium suggests that at least one of the assumptions of the Hardy Weinberg law are violated. But the opposite is not true! For example for certain types of frequency dependent selection or heterozygote superiority, the equilibrium frequencies may match Hardy Weinberg expectations.
• Most importantly allows us to systematically construct mathematical models to understand how evolution operates.
• A puzzler: Hardy Weinberg and multiple alleles

IV. Measuring Genetic variation

A. Explain why we are concerned about genetic variation in studying population genetics and evolution.

• Define genetic polymorphism.
• Define cline and explain how clines might arise. Note that clines related to phenotype are quite common. For instance for mammal species, it is often the case that across a species range, the animals are larger in colder areas of the mammal's geographical range.
• Define temporal variation and explain the significance of the prairie vole example.

B. Identify the main ways scientists identify genetic variation today.

• At protein level using electrophoresis. See p 466 - 467
• Polymorphic loci
• Heterozygosity(H)
• Classical vs neutral mutation model
• What are the advantages and disadvantages of using protein electrophoresis to measure genetic variation?
• At the DNA level
• Restriction Fragment length polymorphisms (RFLPs). See 22.6, 22.7
• Single nucleotide polymorphisms - Protein electrophoresis misses many neutral and silent mutations.
• DNA length polymorphisms - involving insertions/deletions within genes
• Distinguish between synonymous and nonsynonymous changes in a gene and explain which sort of change tends to lead to the higher amount of nucleotide diversity.
• Short tandem repeats (STR's)
  

V. List and discuss the main agents of biological evolution as understood today

A. Mutation

• Source of genetic variation
• Protein synthesis and point mutation review.
• Mutations may be harmful or beneficial or neutral depending on the environment
• Mutation frequencies Table 22.5
• Equilibrium frequency p 472
  

B. Genetic drift

• Explain how allele frequencies can change in the absence of natural selection in terms of sampling error. p 472
• Note sampling variance. = pq/2N
• Define the three ways genetic drift arises. p 473 and distinguish between the bottle neck effect and founder effect.
• Explain why genetic drift is an important consideration in wildlife conservation. See also p 483 for a general discussion of genetics in conservation biology.

C. Migration

• Define gene flow.
• Explain the relationship between gene flow and genetic divergence. Note that population subdivision into small demes increases genetic variance between groups and migration has the opposite effect.

D. Natural selection.

• Define natural selection and explain its significance in understanding evolution.
• Explain the distinction between natural and artificial selection and give examples of natural selection.
• Define Darwinian fitness: page 477
• Compute fitness values and selection coefficients for two allele models. Table 22.6
• Show the general procedure for determining change in allele frequency caused by natural selection. Tables 22.8
• Be able to apply the formulas in your text for change in gene frequency for selection against a recessive trait and for heterozygote superiority(overdominance) p 478-479 and the formulas for balance between mutation and selection on p 481.
• Be able to graphically analyze the behavior of simple two allele models of natural selection and determine the stability of equilibria. Note: Review the online activity: Hardy Weinberg and Natural Selection.

E. Distinguish between the different types of Non random mating p 482

• Distinguish between positive and negative assortative mating. Your book isn't quite correct in its assertion that these sorts of matings have no effect on allele frequencies.
• Define Inbreeding and explain how to use the coefficient of inbreeding. See page 482
• Define sexual selection and give examples. (Not in text)
• Note another form of non random mating is propinquity. Mating preferentially with with geographically nearby individuals. (Not in text)

VII. Discuss the mechanisms by which we believe speciation happens. p 484-486

A. Distinguish between allopatric versus sympatric speciation (not in text)

B. Distinguish between the main types of barriers to gene flow and give examples. See page 484

Note: Prezygotic mechanisms often evolve as adaptations favored by evolution since individuals who avoid mistakes in mating have higher Darwinian fitness.

C. Why is it often thought that younger species isolation tends to involve prezygotic isolating mechanisms.

 

Study Q22.1, and 22.2 on page 486 and be able to do similar problems.

Be able to do questions and problems 22.2, 22.3, 22.6, 22.10, 22.12, 22.17, 22.19, 22.22, 22.14, 22.26, 22.31

pgd 11/01/02 revised 11/16/04