Chapter 16 – The Evolution of Populations and Speciation

1. Chapter 16 – The Evolution of Populations and Speciation

2. Genetic Equilibrium • Population genetics – study of evolution from a genetic point of view. • Evolution – gradual change in the genetic material of a population. • A population is the smallest unit in which evolution occurs.

3. Variation • Measuring frequency of a variation. • Most of the time the differences are shaped like a bell curve. • Most organisms have an average characteristic. • Ex. Length of fish

4. Causes of Variation • Mutation • Recombination • Random fusion of gametes

5. Allele Frequencies and the Gene Pool • Gene pool – total genetic information available in a population. • All the genes in a population that can be expressed in future generations. • Ex. Two forms of allele A and a in a set of 10 gametes. If half the gametes carry the allele A, we can say that the allele frequency of A is 0.5 or 50%.

6. Allele Frequency • Determined by dividing the number of a certain allele by the total number of alleles of all types in the population. • Certain allele = five A allele • Total number of alleles = ten gametes

7. Class Allele Frequency • Brown hair allele frequency • Number of people carrying an allele for brown hair = __________ • Total number of alleles = ________ Is this an accurate calculation?

8. Predicting Phenotype • Phenotype frequency – the number of individuals with a particular phenotype divided by the total number of individuals in the population. • Ex. Four o’clock flowers; 4 pink plants out of 8 plants. 0.5 pink • Pg. 301

9. Genotype Frequencies • Frequency of certain genotypes. ex. Frequency of RR *remember Law of Probability Frequency of R x Frequency of R = Frequency of RR pair 0.75 x 0.75 = 0.5625 (RR) Frequency of r x Frequency of r = Frequency of rr pair 0.25 x 0.25 = 0.0625 (rr)

10. The frequencies of all types must add up to 1.0. 1.0 – frequency of RR – frequency of rr = frequency of Rr 1.0 – 0.5625 – 0.0625 = 0.375 (Rr)

11. Hardy-Weinberg Genetic Equilibrium Wilhelm Weinberg and Godfrey Hardy showed that allele frequencies in a population tend to remain the same from generation to generation unless acted on by outside influences. Hardy-Weinberg genetic equilibrium

12. Requirements for this to be true: • No net mutations occur; allele frequencies do not change overall because of mutation • Individuals neither enter nor leave the population • The population is large • Individuals mate randomly • Selection does not occur

13. Theory • This is theoretical. • Hardy and Weinberg allowed us to see what disrupts equilibrium.

14. H.W. • Pg. 302 • Questions 1-6

15. Ch. 16: sec. 2 – Nonrandom Mating • Many species do not mate randomly. • Most mate by geographic proximity. • This might lead to organisms mating with closely related organisms. • Increasing homozygous recessive genotypes. --- disorders

16. Assortative Mating • Selecting mates with similar characteristics.

17. Natural Selection • The 5th requirement for Genetic Equilibrium.

18. Stabilizing Selection • Individuals with the average form of a trait have the highest fitness. • Extreme forms are selected against. • Allele frequencies stay the same.

19. Directional Selection • Individuals with a more extreme form of a trait are selected for. • Allele frequencies are going in a direction.

20. Disruptive Selection • Individuals with either extreme variation are selected for. • Individuals with the average form are selected against. • This can lead to two different species over time.

21. Glogster Assignment for Sec. 3 • You and a partner are going to create a glogster explaining your assigned term. • Include: explanation/definition, examples, pictures, big idea, your own definition Concepts: 1. Speciation 2. Morphology 3. Biological Species Concept 4. Geographic Isolation/Reproductive Isolation 5. Prezygotic Isolation/Postzygotic Isolation 6. Punctuated Equilibrium