1. Evolution: A change in gene frequency within a population Evolution 201

2. Learning Targets: I can describe Genetic Drift and the conditions required for it to happen. I can describe Genetic Drift and the conditions required for it to happen. I can give examples of Genetic Drift. I can give examples of Genetic Drift. I can define allele. I can define allele. I can differentiate between the three types of Modes of Selection I can differentiate between the three types of Modes of Selection Homework: Homework: study, study, study

3. Look at this diversity

4. A change in Gene Frequency A gene is a section of DNA that codes for a specific trait. A gene is a section of DNA that codes for a specific trait. An Allele is a different version of a gene An Allele is a different version of a gene We get one copy of a gene (an allele) from our father and one copy of a gene (an allele) from our mother. We get one copy of a gene (an allele) from our father and one copy of a gene (an allele) from our mother. Evolution looks at what allele is more or less common. Evolution looks at what allele is more or less common.

5. Alleles:

6. Background: Darwin’s Finches as an Example of (A) Natural Selection

7. Background on (A) Natural Selection From this pattern Darwin recognized that in nature, organisms struggle for existence and that more offspring are born than live to reproduce. He called the ability of an individual to survive and reproduce in its specific environment – fitness. He called the ability of an individual to survive and reproduce in its specific environment – fitness. This fitness is a result of adaptations and only those individuals that are the fittest survive. This fitness is a result of adaptations and only those individuals that are the fittest survive.

8. Background on (A) Natural Selection Those organisms with specific characteristics (adaptations) that allow them to live long enough to reproduce are considered the fittest. Those organisms with specific characteristics (adaptations) that allow them to live long enough to reproduce are considered the fittest.

9. Background on (A) Natural Selection Darwin said that over long periods of time organisms that are the fittest survive passing on those traits to their offspring causing a change in gene frequency. He called this a Descent with Modification. Darwin said that over long periods of time organisms that are the fittest survive passing on those traits to their offspring causing a change in gene frequency. He called this a Descent with Modification.

10. Background: Evolution 201 We know that in genetic terms, Descent with Modification results in alleles being passed to the next generation in proportions that differ from the present generation. We know that in genetic terms, Descent with Modification results in alleles being passed to the next generation in proportions that differ from the present generation. The three mechanisms that alter allele frequencies directly and cause most evolutionary change are The three mechanisms that alter allele frequencies directly and cause most evolutionary change are (A) Natural Selection (A) Natural Selection (B) Genetic Drift (B) Genetic Drift (C) Gene flow (C) Gene flow

11. (B) Genetic Drift Genetic Drift is when chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next…. Genetic Drift is when chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next…. Especially in small populations!!! Especially in small populations!!!

12. What is Genetic Drift? Since Darwin, one of the most important advances in Evolution research has been the recognition of the role of genetic Drift as an evolutionary force Since Darwin, one of the most important advances in Evolution research has been the recognition of the role of genetic Drift as an evolutionary force Genetic drift refers to the power random events can have in influencing whether genes increase or decrease in future populations. Genetic drift refers to the power random events can have in influencing whether genes increase or decrease in future populations.

13. Examples of Genetic Drift: Certain Circumstances can result in genetic drift having a significant impact on a population. Certain Circumstances can result in genetic drift having a significant impact on a population. Conditions for Genetic Drift: Conditions for Genetic Drift: Small Populations Small Populations Random Acts Random Acts Variation with the population Variation with the population Two examples are the founder’s effect and the Bottleneck effect. Two examples are the founder’s effect and the Bottleneck effect.

14. Bottleneck Effect Bottleneck effect is when there is a sudden change in the environment, such as a fire or flood that drastically reduces the size of a population. By chance alone, certain alleles may be overrepresented by the survivors, others may be underrepresented and some may be absent. As generations pass this should lead to substantial effects to the gene pool. By chance alone, certain alleles may be overrepresented by the survivors, others may be underrepresented and some may be absent. As generations pass this should lead to substantial effects to the gene pool.

15. Bottleneck Effect

17. Founder’s Effect

18. Effects of Genetic Drift: A summary Genetic Drift is significant in small populations Genetic Drift is significant in small populations Genetic Drift can cause allele frequencies to change at random Genetic Drift can cause allele frequencies to change at random Genetic drift can lead to a loss of genetic variation within a population Genetic drift can lead to a loss of genetic variation within a population Genetic drift can cause harmful alleles to become fixed. Genetic drift can cause harmful alleles to become fixed.

19. C. Gene Flow Natural Selection and genetic drift are not the only phenomena affecting allele frequency. Natural Selection and genetic drift are not the only phenomena affecting allele frequency. Gene Flow is the transfer of alleles into or out of the population due to the movement of fertile individuals or their gametes. Gene Flow is the transfer of alleles into or out of the population due to the movement of fertile individuals or their gametes.

20. Gene Flow

21. Types of Natural Selection Directional Selection: when natural selection favors an extreme phenotype. Directional Selection: when natural selection favors an extreme phenotype. Stabilizing Selection: favors the middle ground – not the extremes. Stabilizing Selection: favors the middle ground – not the extremes. Disruptive Selection – favors both extremes not the middle Disruptive Selection – favors both extremes not the middle

22. Types of Natural Selection Directional Selection: For example, when the environment selects the fastest deer, most flexible trees, etc. Directional Selection: For example, when the environment selects the fastest deer, most flexible trees, etc.

23. Types of Natural Selection Disruptive Selection: Black-bellied seed cracker finches (in Cameroon). The smallest finches can eat soft seeds while the largest finches can crack the hard seeds. The average size finches can not do either well. Disruptive Selection: Black-bellied seed cracker finches (in Cameroon). The smallest finches can eat soft seeds while the largest finches can crack the hard seeds. The average size finches can not do either well.

24. Types of Natural Selection Stabilizing Selection: For example, human baby weight. Stabilizing Selection: For example, human baby weight.