Microevolution: Unique Gene Pools

1. Microevolution: Unique Gene Pools

2. Learning Objectives • Explain the how Lamarck, Lyell and Malthus influenced Darwin’s thinking. • Describe the four parts of the theory of natural selection. • Explain why natural selection works on phenotypes and NOT genotypes. • Explain why natural selection CANNOT occur without inheritable genetic variation.

3. Learning Objectives • Name the two sources of genetic variation. • Explain why mutations are not the most common source for genetic variation. • Describe the 5 different types of mutations and explain the possible outcomes of each. Provide an example of each. • Explain the difference between artificial and natural selection. • Explain why pseudogenes are referred to as “junk DNA.

4. What is evolution ? • Descent with Modification • Earth’s many species are descendants of ancestral species that were very different from those alive today. • Evolution • change over time in the genetic composition of a population.

5. Charles Darwin Charles Darwin (1809-1882) is credited with proposing that the mechanism for the process of evolution is natural selection. Darwin spent five years on a voyage that took him around the world with the majority of his time spent in South America and its neighboring islands. Darwin published his theory with compelling evidence for evolution in his 1859 book On the Origin of Species, overcoming scientific rejection of earlier concepts of transmutation of species.

6. Jean Lamarck (1744-1829) • 1. Theory of desire • - organisms change due to inborn desire to change to • become more fit for environment • ex: ant eaters develop long snouts • 2. Theory of use and disuse • - organs that are being used get large and strong • - organs that are not used shrink and eventually disappear • ex: snakes- didn’t use legs so disappeared • 3. Theory of inheritance • - acquired traits were passed on to offspring • ex: snakes that lost legs passed trait • Importance: Recognized that species evolve, although explanation was flawed

7. Thomas Malthus • More babies born than deaths • Consequences of overproducing within environment: war, famine, disease • Struggle for existence Thomas Malthus (1766-1834)

8. Charles Lyell • Charles Lyell 1797-1875 • Leading geologist during Darwin’s time • Gradualism: mechanisms of change are slow and constant over time.

9. Charles Darwin He established that all species of life have descended over time from common ancestors, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding.

10. Charles Darwin By the 1870s the scientific community and much of the general public had accepted evolution as a fact. However, many favored competing explanations and it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 1950s that a broad consensus developed in which natural selection was the basic mechanism of evolution. In modified form, Darwin's scientific discovery is the unifying theory of the life sciences, explaining the diversity of life.

11. Figure it out with a partner!! • Selection acts on phenotype. • Explain why differential reproduction and survivorship depend on phenotype not genotype.

12. Figure it out with a partner!! • Natural selection acts on individuals. • Explain why only populations evolve and NOT individuals.

13. Microevolution: Unique Gene Pools

14. Evolution Terms Boot Camp • Genes ~ sequence of DNA nucleotides that code for a trait • Alleles ~ alternate versions of a trait. Ex: B = brown; b = blue • Genotype ~ the set of alleles for a trait. Ex: Bb • Phenotype ~ physical manifestation of a trait. Ex: Blue eyes • Gene Pool ~ collection of all the alleles in a population • Allele Frequency ~ the number of times a specific allele appears in the gene pool • Species-a group of interbreeding organisms that produce viable and fertile offspring in nature

15. Microevolution Microevolution is simply a change in gene frequency within a population. • Evolution at this scale can be observed over short periods of time such as from one generation to the next. • Example: The frequency of a gene for pesticide resistance in a population of crop pests increases quickly.

16. Darwin’s Theory of Natural Selection Individuals that have physical or behavioral traitsthat better suit their environment are more likely to survive and will reproduce more successfully than those without those favorable traits. There are 4 parts to the theory of evolution by mean of natural selection

17. 1. Genetic variation - members of a population often vary in their inherited traits

18. 2. Overproduction - organisms produce more offspring than can survive - leads to competition

19. 3. Struggle to survive - all organisms face constant struggle to survive due to limited resources

20. 4. Survival of the fittest - Fitness refers to an organism’s ability to survive and reproduce in its environment - Individuals best adapted to environment have greater fitness - Over time, favorable traits increase in population, increasing the match between organisms and their environment

21. Relative Fitness • There are animal species in which individuals, usually males, lock horns or otherwise compete through combat for mating privileges. • Reproductive success is usually far more subtle! • Relative fitness is defined as the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.

22. Adaptations enhance an organism’s ability to survive and reproduce. Structural (body parts) Behavioral Physiological

23. Beneficial adaptations depend on environment Beneficial adaptations in one environment may be selected against survival in other environments

24. The Effect of Environmental Change Earth’s environment is ALWAYS changing and can cause a shift in selection pressures. As a consequence, traits or adaptations that were favorable may become unfavorable. Classic Example: The peppered moth

25. The Peppered Moth & The Industrial Revolution The peppered moth, is native to England and exists in two forms, one is dark and the other light with a “peppered” appearance. Birds are its main predator. Prior to the industrial revolution, only 2% of the moths were dark. The industrial revolution produced vast amounts of sulfur dioxide and soot from the burning of coal which altered the environment.

26. Figure it out with a partner!! Propose an explanation why fifty years after the start of the Industrial Revolution, 95% of the moths were dark.

27. Industrial Melanism England has since regulated the burning of coal and as a result, the trees are returning to their original state (A). Consequently, the coloring among the population of moths in Britain has shifted back so that the peppered moths are once again favored.

28. Microevolution can occur in one of several ways: • natural selection • mutations • Immigrants into the population carrying new genes • random natural events

29. Important Key Points • Natural Selection acts on phenotype because differential reproduction and survival depend on physical characteristics not genotype. • Although natural selection occurs through interactions between individual organisms and their environment, individuals do not evolve. Instead, populations evolve over time. • Natural selection can only increase or decrease heritable traits that vary among individuals in a population • Without variation, natural selection cannot occur

30. TWO Sources of Genetic Variation • Mutations, any change in a DNA sequence, can provide new phenotypes, the raw material for evolution. • Meiosis and sexual reproduction produce new recombinants of phenotypes upon which natural selection operates. The wisteria pictured on the right has a mutation causing it to produce white flowers instead of purple flowers.

31. Mutations in General • MOST mutations are recessive and deleterious (fatal). • Mutations occurring in somatic (body) cells cannot be inherited and do not affect future generations. • Only mutations occurring in gametes are heritable. • Mutations can occur at either the gene or chromosomal level. Mutations may cause a sheep to have a 5th leg. But this is not evolution!

32. 1) Point Mutations: Point mutations occur when one nucleotide is substituted for another.

33. Genetic Code & Synonyms The genetic code contains “synonyms” for the coding of amino acids. For example the DNA codons GGA, GGG, GGT, GGC all code for the amino acid proline. This sort of mutation is called a synonymous or silent mutation.

34. C Called Synonymous because the substitution results in the same amino acid in the sequence. Called silent because the mutated protein is the same as the original protein

35. Nonsynonymous Point Mutations C Point mutations that do result in a different amino acid are called nonsynonymous or missense mutations.

36. Nonsynonymous Point Mutations Missense mutations can affect the protein in one of THREE ways: (Remember the new amino acid will have a different R group on the protein) It can result in a protein that does not function as well as the original protein. (This happens most often.) It can result in a protein that functions better than the original protein. It can result in a protein that functions like the original protein. This is usually because the R groups are similar.

37. Nonsynonymous Point Mutations Another type of nonsynonymous mutation is referred to as a nonsense mutation. In a nonsense mutation, the altered nucleotide sequence results in a premature stop codon which produces a truncated, incomplete and usually nonfunctional protein.

38. Talk with a partner!! Explain the three types of point mutations. Use the following terms in your explanation: synonymous, silent, nonsynonymous, missense and nonsense

39. 2) Frameshift Mutation • A frameshift mutation occurs as a result of either an insertion or deletion of a nucleotide. • This changes the amino acid sequence of the protein from that point forward. • Almost all frame shift mutations are deleterious.

40. 2) Frameshift Mutation Example • Recently, bacteria were found growing in a pool of nylon wastes. (Flavobacterium) • These bacteria were actually digesting the nylon waste. • Upon examining the genome of these bacteria, it was found there was a frameshift mutation in their DNA that caused the production of three different enzymes that could digest the nylon.

41. 3) Gene Duplication • Any duplication of a region of DNA that contains a gene.

42. 3) Gene Duplication Genes can also be duplicated and occasionally the duplication moves a gene from one chromosome to another. Each gene will accumulate different mutations altering the protein that is produced.

43. 3) Gene Duplication Example Myoglobin is a protein that binds with oxygen in the muscles. This gene has been duplicated and modified many times. Many of the duplications are introns – noncoding segments of DNA. While some of the modified genes are exons which code for functional proteins. It has given rise to the hemoglobin gene.

44. Evolution of Hemoglobin Gene by Duplication

45. Pseudogenes • Pseudogenes are inheritable genetic elements that are similar to functional genes but are non-functional as they do not encode for proteins. • Their biogenesis results from the duplication of a parental gene, or the transposition of an mRNA sequence into different place in the genome • Pseudogenes can collect multiple mutations because they are not subject to natural selection….Why? • Often referred to as “junk” DNA

46. Pseudogenes

47. 4) Neutral Mutations • Naturally evolving proteins gradually accumulate neutral mutations at a predictable rate. Neutral Mutations do not always affect the function of the protein and forms the basis for the molecular clock. • EX: Cytochromec, a small protein found on the mitochondrial membrane. • Between mammals and reptiles there are 15 different amino acids or mutations.

48. 4) Neutral Mutations • Mammals and reptiles diverged 265 million years ago. • That means on average cytochromec mutated every 17 million years. • In comparing the evolution of other organisms and their cytochromec one mutation every 17 million years holds true.

49. Changes in Cytochrome C Above is a comparison ancestral cytochrome c and human cytochrome c. This gene has been highly conserved as it is a protein used in the electron transport chain of the mitochondria. Missense mutations occur more frequently in pseudogenes than in functional genes.

50. Talk with a partner!! Although cytochrome c is NOT a pseudogene, why would missense mutations occur more frequently in pseudogenes than in functional genes?