1. Chapter 16 Evolution of Populations

2. What Darwin Did Not Know He did not know how traits were passed on from one generation to the next. He did not know how variations appeared.

3. Genetic Variation Remember: genes have at least 2 forms (alleles) Sources of genetic variation: 1. Mutation – change in a sequence of DNA 2. Gene Shuffling – genes move about during the production of gametes (sex cells)

4. Variation and Gene Pools Remember – a population is a group of individuals of the same species that interbreed. Because they interbreed, the group of genes is called the gene pool Gene pool – all the genes in a population

5. Relative Frequency The number of times that the allele occurs in a gene pool Expressed in percentage Ex. Mouse population – relative frequency of the dominant allele (black fur) is 40% *In genetic terms – evolution is any change in the relative frequency of alleles in a population.

6. Single-Gene and Polygenic Traits The number of phenotypes produced for a given trait depends on how many genes control the trait Single-Gene: one gene, two alleles Ex. Widow’s Peak Polygenic Traits: traits controlled by two or more genes Ex. Height

7. Genetic Drift More common in small populations (small gene pool) Individuals that have a certain trait may have more offspring Over time, the trait becomes more common in the population

8. Genetic Drift http://evolution.berkeley.edu/evosite/evo1 01/IVBMechanisms.shtml

9. 16-3: Speciation Speciation – formation of new species As new species evolve, populations become reproductively isolated from each other Reproductive isolation

10. Other Types of Isolation Geographic Isolation – two populations are separated by geographic barriers Ex. Rivers, Mountains Abert squirrel & Kaibab squirrel: Grand Canyon Temporal Isolation – two or more species reproduce at different times Ex. 3 species of orchids release pollen on a different day

11. Galapagos Finches Darwin thought they were completely different types of birds. Natural selection shaped the beaks of different bird populations as they adapted to eat different foods. Since Darwin, the Grant’s have studied the finch populations for years.

12. Galapagos Finches Grants’ work showed that finch beak size can be changed by natural selection. Birds with different sized beaks had different chances of survival during a drought. Scarce food sources = birds with largest beaks survive Next generation – birds with larger beaks

13. Process of Speciation 1. Founders Arrive 2. Geographic Isolation 3. Changes in the Gene Pool 4. Reproductive Isolation 5. Ecological Competition 6. Continued Evolution