16-1 Genetic Equilibrium

1. 16-1 Genetic Equilibrium Chapter 16 Population Genetics and Speciation

2. Terms to Know • Population genetics – study of evolution from a genetic point of view • Microevolution – evolution at the genetic level • Bell Curve – most members of the population have similar traits; only a few are at the extremes • Can SHIFT over time!!!

4. Variations of Traits Within a Population • Causes of Variation • Mutations • TAGATC -> TAAATC • Recombination (crossing-over and independent assortment) • (during meiosis – see pic!) • Random pairing of gametes • Which sex cells combine successfully

5. The Gene Pool • Gene pool = the total genetic information available in a population • Allele Frequency = number of a certain allele / total number of alleles in a population • Calculated by … # of allele A total # of A and a

6. What is the allele frequency? • Half a population of four o clocks are red/ half are white. • What is the frequency of the r allele? • 0.50 or 50%

7. The Gene Pool • Phenotype Frequency = # of individuals with a phenotype / total # of individuals within the population

8. The Gene Pool • Phenotype Frequency = # of individuals with a phenotype / total # of individuals within the population • # red flowers/ Total # of individuals

9. Hardy – Weinberg Genetic Equilibrium • Ideal hypothetical population that is not evolving (ie not changing over time) • 5 criteria (must be met) • No net mutations occur • No one enters or leaves the population • The population is large • Individuals mate randomly • Selection does not occur Why might a population never be in HW genetic equilibrium???

10. 16-2 Disruption of Genetic Equilbrium

11. Mutation • Gene flow – the process of genes moving from one population to the next - Immigration - Emigration 3. Genetic Drift – allele frequencies in a population change usually because the population is small

12. 4. Nonrandom mating – mate selection is influenced by geographic proximity, mates with similar traits, and sexual selection

13. 5. Natural Selection – some members are more likely to survive and reproduce - stabilizing selection - disruptive selection - directional selection

14. Types of Selection • Stabilizing selection - individuals with average forms of a trait have the highest fitness • Ex. Large lizards will be spotted by predators; small lizards can’t run fast enough to get away from predators

15. Types of Selection • Disruptive Selection – individuals with either extreme of the trait has the greatest fitness • Ex. White moths on white trees cannot be seen; Dark moths on dark trees cannot be seen; medium colored moths will be seen on both trees (eaten by birds)

16. Types of Selection • Directional selection – more extreme form of a trait has the greatest fitness • Ex. Anteaters with the longest tongues will get the most food

18. 16-3 Formation of Species

19. The Concept of Species • Speciation – the process of species formation • Morphology – internal and external appearance of an organism • Species – morphologically similar and can interbreed to produce fully fertile offspring

20. Morphological vs Biological Species Concept • 2 competing concepts (ideas) on how to determine different species • Morph = based solely on appearance • Bio = based on who can reproduce with who successfully (not useful for extinct or asexual organisms) • What do we use today? • Mix of BOTH!!!

21. Isolation and Speciation • Geographic isolation – physical separation of members of a species • Ex. River dries up into several small pools; fish diverged enough to be considered separate species

22. Reproductive Isolation – species become genetically isolated • Ex. The offspring of interbreeding species may die early or may not be fertile • Ex. Different mating times

23. Rates of Speciation • Gradualism – speciation occurs at a regular, gradual rate • Punctuated Equilibrium – sudden, rapid change then long periods of no change