Chapter 16 Evolution of Populations

1. Chapter 16Evolution of Populations Wakefield 2010-2011

2. Gene & Variation16 - 1 • Gene Pool – • Consist of all genes, including all the different alleles, that are present in a population

3. Gene & Variation16 - 1 • Relative Frequency – • The number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur

4. Relative Frequency – Sample Population Frequency of Alleles allele for brown fur allele for black fur 48% heterozygous black 16% homozygous black 36% homozygous brown

5. Frequency of Widow’s Peak 100 80 60 40 20 0 Frequency of Phenotype (%) Widow’s peak No widow’s peak Phenotype

6. Gene & Variation16 - 1 • Single Gene Trait – • Trait that is controlled by a dominant a single gene that has 2 alleles – such as a dominant over recessive trait • Examples are widow’s peak , rolling your tongue, flower or seed color in peas, etc.

7. Gene & Variation16 - 1 • Polygenic Trait – • Traits that are controlled by more than 2 genes • Examples are height, hair color, skin color, Eye color etc.

8. Evolution as Genetic Change16-2 • Directional Selection – • Occurs when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end of the curve

9. Evolution as Genetic Change16-2 • Directional Selection – • Occurs when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end of the curve Low mortality, high fitness High mortality, low fitness

10. Evolution as Genetic Change16-2 • Stabilizing Selection – • Occurs when individuals near the center of the curve have higher fitness than individuals at either end of the curve Stabilizing Selection Low mortality, high fitness High mortality, low fitness Selection against both extremes keep curve narrow and in same place.

11. Evolution as Genetic Change16-2 • Disruptive Selection – • Occurs when individuals at the upper & lower ends of the curve have higher fitness than individuals near the middle Disruptive Selection Largest and smallest seeds become more common. Low mortality, high fitness Population splits into two subgroups specializing in different seeds. Number of Birdsin Population Number of Birdsin Population High mortality, low fitness Beak Size Beak Size

12. Evolution as Genetic Change16-2 • Genetic Drift – • Random change in allele frequency • Occurs in smaller populations and results in the populations being farther from what the laws of probability predict

13. Evolution as Genetic Change16-2 • Founder Effect – • Occurs when allele frequencies change as a result of the migration or isolation of a small subgroup of a population Shown in this image is polydactyly -- extra fingers or sometimes toes -- one symptom of Ellis-van Creveld syndrome. The syndrome is commonly found among the Old Order Amish of Pennsylvania, a population that experiences the "founder effect." Genetically inherited diseases like Ellis-van Creveld are more concentrated among the Amish because they marry within their own community, which prevents new genetic variation from entering the population. Children are therefore more likely to inherit two copies of the particular recessive genes that lead to genetic disease

14. Founding Population Sample of Original Population Descendants Founding Population A Founding Population B

15. Evolution as Genetic Change16-2 • Hardy–Weinberg principle - • States that allele frequency in a population will remain constant unless one or more factors cause those frequencies to change

16. Evolution as Genetic Change16-2 • Genetic Equilibrium – • the situation in which allele frequencies remain constant • Factors necessary for genetic equilibrium: • Random mating • Large population • No movement in or out of the population • No mutations • No natural selection

17. The Process of Speciation16-3 • Speciation – • The formation of a new species

18. The Process of Speciation16-3 • Reproductive Isolation – • As new species evolve, populations become reproductively isolated from each other • When the members of 2 populations cannot interbreed and produce fertile offspring

19. The Process of Speciation16-3 • Behavioral Isolation – • Occurs when 2 populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior The eastern meadowlark (left) & the western meadowlark have overlapping rages and can reproduce but don’t because they have different mating songs

20. The Process of Speciation16-3 • Geographic Isolation – • Occurs when 2 populations are separated by geographic barriers such as rivers, mountains or bodies of water

21. The Process of Speciation16-3 • Temporal Isolation – • Occurs when 2 or more species reproduces at different times

22. The Process of Speciation16-3 • Genetic Variation – • Genotypic / Phenotypic variations caused by changes in gene pools • Caused by - • Mutations • New genes being introduced into a gene pool • Genes exiting a gene pool

23. The Process of Speciation16-3 • Natural Selection – • The process by which individuals that are better suited to their environment survive and reproduce most successfully • aka – “survival of the fittest”

24. The Process of Speciation16-3 • Speciationin the Galapagos Islands– • Occurred by: • Founding of a new population • Geographic isolation • Changes in the new population’s gene pool • Reproductive isolation • Ecological Competition