1. Evolution of Populations Chapter 16

2. Genetic Variation Heterozygotes make up between 4-8% in mammals and 15% in insects. The gene pool is total of all the alleles in a population. All the genes. Relative Frequency is the number of times a particular allele appears in a gene pool. In genetic terms evolution is any change in relative frequency in a gene pool.

3. Relative Frequencies of Alleles Sample Population 48% heterozygous black 36% homozygous brown 16% homozygous black Frequency of Alleles allele for brown fur allele for black fur Brown is the recessive trait but more common in frequency.

4. Sources of Variation The two main sources for genetic variation are Mutation and Gene Shuffling. Mutations occur as DNA is changed by mistakes in replication, radiation or chemicals in the environment. Gene Shuffling occurs as meiosis creates gametes. Crossing Over and Independent Assortment creates new combinations.

5. Single Gene & Polygenic Traits Single-gene traits are controlled by one gene with two phenotypes. The variation leads to only two phenotypes. Polygenic traits are controlled by two or more genes and have variable phenotypes. The phenotypes usually fall in a bell curve.

6. Frequency of Phenotype Phenotype (height) Generic Bell Curve for Polygenic Trait

7. Natural Selection on Single-gene Traits Evolutionary fitness can be measured by the ability to reproduce and pass genes. Natural selection works only on the organism and its phenotype to survive. Natural selection on a single-gene trait can change gene frequencies and cause evolution. Fig 16-5 Red, Brown, & Black Lizards

8. Natural Selection on Polygenic Traits Natural Selection on Polygenic traits is more complex. Directional Selection: occurs when members on one end of the curve have greater fitness and create a shift in that direction Stabilizing Selection: the middle of the curve is most fit and the ends shrink. Disruptive Selection: the lower and upper ends of the curve have greater fitness and the middle declines.

9. Directional Selection Food becomes scarce. Key Low mortality, high fitness High mortality, low fitness Graph of Directional Selection

10. Key Percentage of Population Birth Weight Selection against both extremes keep curve narrow and in same place. Graph of Stabilizing Selection Low mortality, high fitness High mortality, low fitness Stabilizing Selection

11. Disruptive Selection Largest and smallest seeds become more common. Number of Birds in Population Beak Size Population splits into two subgroups specializing in different seeds. Beak Size Graph of Disruptive Selection Number of Birds in Population Key Low mortality, high fitness High mortality, low fitness

12. Genetic Drift In small populations random mating leads to a change in gene frequency called Genetic Drift. By chance in a small population some organisms might leave more offspring thus increasing their gene frequency. The founder effect occurs when a new population is created from an existing one and the founding gene frequency is different than the original population due to chance.

13. Sample of Original Population Founding Population A Founding Population B Descendants Genetic Drift

14. Evolution vs. Genetic Equilibrium Hardy-Weinberg Principle states that allele frequencies will remain in genetic equilibrium and unchanged unless acted upon by evolutionary forces. There are five conditions for Hardy-Weinberg to work: –Random mating –Very large population –No movement in or out of a population –No mutations –No natural selection

15. Speciation Speciation is the process of a species evolving into a new species. Separation of the gene pool is necessary for speciation to occur. –Behavioral Isolation: differences in mating rituals lead to isolation –Geographic Isolation: a population is divided by a geographic boundary. River, mountains –Temporal Isolation: different breeding times separate a population.

16. Concept Map results from which include produced by which result in Reproductive Isolation Isolating mechanisms Behavioral isolationTemporal isolation Geographic isolation Behavioral differencesDifferent mating times Physical separation Independently evolving populations Formation of new species

17. Testing Natural Selection Peter & Rosemary Grant tested Natural Selection on the Galapagos Islands. Variation in the Finches followed the bell curve and was genetic. During drought bigger beaked birds were naturally selected, also a behavior for big beaked birds mating with like birds led to directional selection. The finches’ beaks became bigger in only a few decades.

18. Speciation in Darwin’s The species of Galapagos finches evolved by: –Founding population from South America –Separation by geographic boundaries –Changes in gene pool by directional selection –Reproductive Isolation keeps birds separate –Ecological Competition may change the original population –Evolution continues on the islands –Discuss Limits and Questions to finch evolution