1 / 66

EVOLUTION

EVOLUTION. How living things change over time…. POPULATION GENETICS. Study of allele frequencies within a population. POPULATION - individuals of the same species living in a particular area. Definitions.

cameo
Download Presentation

EVOLUTION

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. EVOLUTION How living things change over time…

  2. POPULATION GENETICS Study of allele frequencies within a population. POPULATION - individuals of the same species living in a particular area.

  3. Definitions Allele-any of the alternative versions of a gene that produces distinguishable phenotypic effects Genotype-the genetic makeup, or set of alleles of an organism Phenotype-the physical and physiological trants or an organism which are determined by its genetic makeup

  4. A GENE POOL is all alleles in a population A = normal a = sickle cell

  5. Frequency of the sickle cell allele in 1980? • Frequency of the sickle cell allele in 2003? • Has evolution occurred in this population? .13+.25 = .38 .17+.25 = .42 YES! REMEMBER: populations evolve, not individuals within the population. MICROEVOLUTION - change in allele or genotype frequencies within a population over time.

  6. HARDY-WEINBERG PRINCIPLE If a population is stable, then allele frequencies in a gene pool do not change from generation to generation and there is NO evolution. • CONDITIONS: • No new mutations • Random mating • No migration • Large population size • No natural/artificial selection

  7. TO CALCULATE GENOTYPE FREQUENCIES: p2 + 2pq + q2 = 1 p2 = frequency of individuals with AA genotype q2 = frequency of individuals with aa genotype 2pq = frequency of individuals with Aa genotype

  8. TO CALCULATE ALLELE FREQUENCIES: p + q = 1 p = frequency of one allele (A) q = frequency of another allele (a)

  9. EXAMPLE #1 The frequency of a dominant allele is 70%, what is: 30% • the frequency of the recessive allele? .49 • p2? • 2pq? • q2? .42 .09

  10. EXAMPLE #2 The frequency of the sickle cell trait is 25%, what is the frequency of: .5 • the recessive allele? .5 • the dominant allele? • carriers? .5 or 50%

  11. EXAMPLE #3 The frequency of a dominant phenotype is 36%, what is the frequency of: .8 • the recessive allele? .2 • the dominant allele? • carriers? .32

  12. EXAMPLE #4 If in a population of 500 rabbits, 80 show the recessive trait of grey fur, what is the frequency of the recessive allele? 80/500 = .16 = q2 If q2 = .16, then q = .4 We could then determine the p value: p = .6

  13. GENETIC EQUILIBRIUM vs. MICROEVOLUTION • GENETIC EQUILIBRIUM • allele frequencies constant generation to generation • population NOT evolving • Hardy-Weinberg used to calculate allele frequencies (p & q) • MICROEVOLUTION • allele frequencies change generation to generation • population is evolving • allele frequencies deviate from Hardy-Weinberg predictions

  14. FACTORS THAT CHANGE ALLELE FREQUENCIES OF A POPULATION MUTATIONS Change in DNA sequence = conversion of allele(s) Source of variation for evolution. Point, deletions, chromosome translocations, transposable elements, lysogenic viruses, gene duplications

  15. NON-RANDOM MATING Sexual selection - choose most fit as mate Kin selection - only certain members of population mate (e.g. honeybees) Inbreeding - breed with close relatives (e.g. Amish)

  16. GENE FLOW Movement of genes into or out of a gene pool. Caused by IMMIGRATION or EMIGRATION

  17. GENETIC DRIFT Random change in small population (note increase in brown allele frequency) BOTTLENECKS - catastrophic events result in only a few survivors FOUNDERS - small # of individuals leave a large population and interbreed

  18. NATURAL SELECTION Most fit for environment survives, reproduces, and becomes more common. Major force of evolution.

  19. THEORY OF NATURAL SELECTION Darwin & Wallace (1858) observed: • organisms on islands resemble those on the closest mainland more than others • organisms differ from island to island • selective breeding induces changes in populations • more organisms are born than survive to reproduce • in any population, variation exists • some variations are inherited

  20. DARWIN’S NATURAL SELECTION VARIATION - individuals in a population exhibit differences - Darwin had no method for producing variation OVERPRODUCTION - populations produce more offspring than can survive (Thomas Malthus) STRUGGLE FOR EXISTENCE - competition in a population for limited resources ”survival of the fittest” DIFFERENTIAL REPRODUCTIVE SUCCESS - evolutionary success = contribution to next generation’s gene pool

  21. What Evolution is Not

  22. CONCLUSION: individuals with favorable variations are more likely to survive to reproduce; leads to differential survival of phenotypes • How do variations arise and get passed down? • Mendel’s work solved this in 1901!

  23. SYNTHETIC THEORY OF EVOLUTION Integrates Darwin’s theory of natural selection with Mendel’s mechanisms for inheritance patterns. Inheritable variations are produced by chance mutations. Eye color Size and shape of ears

  24. Variations that are favorable for the environment are selected for… These organisms survive, reproduce, and become more common in future generations.

  25. Evolution is when populations (not individuals) change over time… “Evolution has no purpose. Evolution has no direction. Organisms become better adapted to their environment and that is all.”Darwin

  26. Artificial Selection Artificial selection occurs when we intentionally breed animals or plants for certain traits.

  27. EVIDENCE FOR EVOLUTION Fossil Record Anatomy and homologous structures Molecular biology Comparative Embryology “Nothing in biology makes sense except in the light of evolution” Dobzhansky, 1973

  28. THE FOSSIL RECORD Evidence of once living organisms shows that organisms have changed over millions of years. They show evolution of forms through time and many transitions among species.

  29. STRATIFICATION OF FOSSILS - location determines a time frame; oldest fossils at bottom of sedimentary rock. RADIOACTIVE DATING used to date materials based on the decay of naturally occurring isotopes; a significant source of information about the rate of evolutionary change.

  30. Python with hind limb buds. Naked mole rats have non-functional eyes. VESTIGIAL STRUCTURES exist, but are no longer functional… EXAMPLES: human tailbone, appendix, and wisdom teeth; flowers of asexual dandelion, pelvis of whale and snake

  31. HOMOLOGOUS STRUCTURES have similar structure, but a different function. Likeness in structure shows descent from a common ancestor…revealed by comparing anatomy

  32. EXTINCTION describes organisms that once thrived but no longer exist… Passenger pigeon Dodo bird Cresent Nailtail wallaby

  33. MOLECULAR BIOLOGY Shows how certain molecules are similar among different organisms… • same DNA nucleotides • same amino acids • same genetic code • same ATP energy molecule • similar gene sequences • similar amino acid sequences Humans share 79% of their genes with chickens!

  34. BACTERIA Shows that the DNA of an organism can change in one generation! • transduction, transformation, and conjugation • resistance to antibiotics spreads as resistant bacteria survive to reproduce

  35. COMPARATIVE EMBRYOLOGY Shows common development of embryos in vertebrates. Developmental resemblances hint at common ancestry…

  36. STABILIZING SELECTION • Favors the norm (average) • Eliminates extremes & diversity, less variation Siberian Huskies are well designed for working in the snow. A heavier dog moves slower and sinks into the snow. A lighter dog isn’t strong enough to pull sleds, giving it little value as a working dog.

  37. DISRUPTIVE SELECTION • Favors individuals at both extremes • Greater variation • DIRECTIONAL SELECTION • Favors a single allele • Advantageous allele increases in frequency, regardless of dominance • Less variation

  38. Genetic variations in a population are required for selection to occur. Factors that increase genetic variability: 1. MUTATION - random DNA changes introduce variation…sometimes at great benefit to the organism. 2. LARGE POPULATIONS

  39. 3. SEXUAL REPRODUCTION Meiosis - independent assortment, crossing over Fertilization - different diploid cells • 4. HETEROZYGOTE ADVANTAGE • Heterozygote has higher relative fitness than either homozygous condition. • Sickle cell allele is present in high proportions in Africa. Homozyous is harmful, but heterozygous provides protection against malaria. • Disadvantage - lethal allele not eliminated

  40. 5. DISRUPTIVE SELECTION • Selection pressures act against individuals in the middle; two phenotypes emerge 6. IMMIGRATION - gene flow into the population • 7. BALANCED POLYMORPHISM • Environmental conditions favor the presence of multiple alleles (phenotypes) in a population. • Humans have A, B, and O alleles for blood.

  41. Factors that DECREASE genetic variability: 1. Asexual reproduction 2. Directional selection - favors 1 extreme 3. Stabilizing selection - favors average 4. Emigration 5. Small populations 6. Kin selection

  42. 7. Sexual selection • organisms maximize reproductive potential • many behavioral differences between males/females related to size/quantity of gametes • small sperm energetically cheap to produce compared to large, nutritive eggs

  43. What do males do? What do females do? Disadvantage: “best fit” is not always best for survival in environment Neutral mutations do not affect genetic variability no advantage or disadvantage to population 90% of eukaryotic DNA never used usually only 1st 2 bases determine a.a.

  44. These happy face spiders look different, but they can interbreed… so they are from the same species…Theridion grallator SPECIATION A species consists of individuals that are able to breed and produce FERTILE offspring in nature. 1.75 million species named and described. Estimated 10-100 million total different species

  45. MACROEVOLUTION Large-scale changes over a long time have made it possible for millions of species to evolve. Occurs in a population by change in gene pool due to REPRODUCTIVE ISOLATION population ---> isolated ---> new species

  46. ALLOPATRIC SPECIATION Speciation due to geographical isolation. One pop. split into 2 isolated pops. by natural event Each pop. has different mutations Each pop. has different variations Each lives in different environment

  47. Different variations favorable in each environment Different variations survive, reproduce and become common No gene flow for millions of years Two species evolve if they cannot interbreed & produce fertile offspring

  48. PREZYGOTIC ISOLATION Organisms aren’t able to mate (before formation of a zygote) Habitat isolation - species live in different habitats within the same range Temporal isolation - breed at different times

  49. Mechanical isolation - genital organs of organisms are incompatible Size differences make mating impossible. Behavioral isolation - different courtship behaviors (phermones, dance, song) Male wood and leopard frogs have vocalizations that only attract females of their own species.

More Related