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A return to our senses

A return to our senses. 9/28/09. If chromosomes misalign, recombination leads to gain of gene on one chromosome and loss of gene on the other. Tandem arrays of genes. 1. Gene duplications by mismatched recombination. Human chr 3. Human chr Z. 2. Insertion of retrotranposed gene. Fugu fish

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A return to our senses

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  1. A return to our senses 9/28/09

  2. If chromosomes misalign, recombination leads to gain of gene on one chromosome and loss of gene on the other. Tandem arrays of genes 1. Gene duplications by mismatched recombination

  3. Human chr 3 Human chr Z 2. Insertion of retrotranposed gene Fugu fish scaffold 830 Rh1 Fugu Rh gene has been inserted into chromosome

  4. 3. Gene duplication as part of whole genome duplication Meiosis n 2n chromosomes Gametes

  5. 3. Normal fertilization Sperm + Egg Zygote 2n chromosomes

  6. 3. Failure of meiosis Nondisjunction Gamete, 2n chromosomes

  7. Genome duplication + Zygote, 4n

  8. Evidence that genome duplication occurs • Genome size varies between organisms • Prokaryotes 0.6 Mb 500 genes • E coli 4.7 Mb 6000 genes • Human 3400 Mb 25,000 genes • Chromosome # varies (2n) • Drosophila 8 • Human 46 • Chicken 78 • Lamprey 168

  9. Other evidence • If duplicate whole chromosome, will see many genes duplicated • See similar trees for all genes • See similar gene order on two duplicated chromosomes

  10. G protein subunit tree

  11. Chromosome arrangement Tandem duplication and then chromosomal duplication

  12. Synteny • “the preserved order of genes on chromosomes of related species, as a result of descent from a common ancestor” • Chromosomes can break and stick back together

  13. LWS RH2 RH1 SWS2 SWS1

  14. Chromosomes containing opsin genes came from duplicates Chromosomal duplication and then tandem duplication SWS1 = OPN1SW LWS = OPN1LW RH1 = RHO

  15. Vertebrate genome duplications 2x 2x 2x Kumar and Hedges 1998 Lamprey

  16. Gene duplicate divergence times Genome duplication in fishes 350 Mya Meyer and van der Peer 2005

  17. G protein pathway in rods

  18. Phototransduction proteins

  19. Phototransduction proteins

  20. Sources of gen(om)e evolution: • Nucleotide sequence - coding sequence • Regulatory sequence - alter gene expression • Gene splicing - alter exon combos • Gene duplication • Segmental duplication • Chromosomal duplication • Genome duplication

  21. How fast do these things happen - DNA mutation? • Each nucleotide will mutate (change) every 100-500 MY • Entire genome will change in 500 MY • Some nucleotides change a lot - others not very much • Depends on selection

  22. substitutions/site * 109 Li and Graur 2003 Codons Non-Syn Synonymous

  23. How fast do these things happen - genome duplication? • Genome duplications have occurred 3-4 times in vertebrate history (1 per 100 MY) • Get 3-4 copies of each gene

  24. How fast do these things happen - gene duplication? • Any given gene will duplicate on average every 100 MY • Get 3-4 copies of every gene • But most of duplicates will go nonfunctional in about 4 MY

  25. How fast do these things happen? - Summary • Genome duplications have occurred 3-4 times in vertebrate history (1 per 100 MY) • Any given gene will duplicate on average every 100 MY • Each nucleotide will mutate (change) every 100-500 MY

  26. Goals for rest of semester • How do sensory cells function? • Structural basis • Molecular basis • How has gen(om)e evolution shaped sensory systems? • Why are animals the way they are?

  27. Sensory organs

  28. Receptors

  29. What are senses good for? • Convert outside stimuli to neural signal • Stimulus causes a conformational change in a receptor molecule • This causes change in membrane potential through ion channel • This sends neural signal

  30. Sensory transduction • Ionotropic • Receptor change directly alters membrane potential • Receptor IS the ion channel • Iono - ions • -tropic affecting

  31. Sensory transduction • Ionotropic • Ligand gated ion channel

  32. Sensory transduction • Metabotropic • Receptor change activates G protein which activates effector molecule which opens / closes ion channel • Indirect link to ion • channel • Metabo- change • -tropic affecting

  33. Can be both ionotropic and metabotropic receptors for same ligand, e.g. Glutamate receptors

  34. Role of membrane • Most sensory cells rely on receptor • Integral to membrane • Cells contain special sensory membrane • More membrane = more receptors  More sensitivity

  35. Ways to maximize membrane #1 • Microvilli • Evagination - out pocketing • Strengthen with actin fibers - can be tightly packed

  36. Kinds of microvillar sensory cells • Hair cells • Invertebrate photoreceptors

  37. Ways to maximize membrane #2 • Cilium • Evagination • Based on tubulin • Typically 9 double microtubules • surround 2 central • microtubules • 9+2

  38. Cilia • Olfactory receptors • Photoreceptors

  39. Membrane organization • Sensory membrane is specialized • Region of cell where receptor and other proteins transduce signals • Helpful to localize proteins • Attach to scaffolding proteins • Tether to membrane

  40. Drosophila photoreceptor • 50,000 microvilli • INAD-scaffolding protein • 5 protein binding domains • Interconnect transduction proteins Figure 2.5

  41. Vertebrate rods - integral vs tethered proteins

  42. Membrane renewal • Signal transduction is high stress • Need to fix damage • Replace sensory membrane • Vertebrate photoreceptors • Invert photoreceptor membrane totally disintegrates • Replace entire cell • Olfactory and taste cells

  43. Phagocytosis of sensory membrane

  44. Olfactory cell half life - 90 days Regrow from basal stem cells

  45. Olfactory cell half life - 90 days Replace each of the 100-1000 cells. Have to find right connection when replaced.

  46. Taste buds • Half life is approximately 10 days • Need to make correct neural connections • How does this happen????

  47. External specializations • Extra structure to enhance function • Protection • Decrease sensitivity • Increase sensitivity

  48. Protection

  49. Pressure detection by palicinian corpuscle Layers decrease sensitivity Most sensitive to pressure change

  50. StatocystsCells of equilibrium Hollow sphere with 400 mechanoreceptors in bristles Statolith - sand grain mass As lobster moves, statolith stimulates different cells and determines orientation

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