1. Population Genetics II. Natural selection and the genetic makeup of populations: Natural selection + limited gene flow = adaptation to local conditions Example: metal tolerance on a site contaminated with mine tailings

2. Clines The gradient in allele occurrence across a set of populations due to natural selection Example: leaf hairiness in Spergula arvensis Hairy plants increase In frequency with latitude

3. Another example of a cline Flower scent in Polemonium viscosum: high altitude: bumblebee pollination low altitude: flies also pollinate it

4. Clines illustrate directional selection over a range of environmental conditions…. …directional selection? Better survival and reproduction for organisms at one end of the phenotypic distribution

5. Other types of selection Stabilizing selection: The mean phenotype is favored by natural selection Disruptive selection: The extremes of the phenotypes have higher fitness than mean phenotype Fitness?....

6. A graphical illustration… (Silvertown and Charlesworth 2001, p. 77)

7. Some real examples: Directional selection: widowbirds Galapagos Finch beaks

8. Some real examples… Stabilizing selection: flowering time in Senecio integrifolius Another example: birth weight in human babies

9. Some real examples… Disruptive selection: Garter snake coloration and behavior

10. Other types of selection Balancing selection: the heterozygote advantage Example: sickle cell anemia.

11. Other types of selection Negative frequency dependence: the rare alleles have the advantage Example: Self-incompatibility alleles in plants Mechanism by which genetic diversity is maintained

12. Ipomea purpurea flowers Other types of selection Positive frequency-dependent selection Can lead to loss of genetic diversity

13. The mutation-selection balance and mutation load Even while natural selection acts to eliminate deleterious mutations, new mutations are being formed An equilibrium exists between the creation of new mutations and their elimination by natural selection This is the mutation selection balance

14. The mutation-selection balance and mutation load The mutation load is made up of the generally low frequencies of deleterious alleles found in the population Alleles that are dominant are removed more quickly, and maintained at lower frequencies, than recessive deleterious alleles

15. Determining level of isolation: Burrowing owls Population genetics and conservation Population genetics is used throughout conservation biology, in a number of different ways

16. Population genetics and conservation Genetics is used to infer evolutionary relation- ships and define management units. Example: coho salmon stocks evolutionarily significant units

17. Population genetics and conservation Captive breeding programs Minimize inbreeding and maintain as much genetic diversity as possible

18. Population genetics and conservation Measures of genetic diversity indicate past events and possible management issues

19. Population genetics and conservation Patterns of genetic diversity among populations: Inferring rate of spread of organisms Inferring past geological/climatic processes

20. Ungraded homework assignment List the three major types of selection and give an example of each.