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Lecture 16

Lecture 16.docx

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Biology 1002B
Denis Maxwell

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Lecture 16: Evolution of Multicellularity 1. Identify the function of caspases.  Apotosis – gene activation from receptors signals on surfaces of marked cells e.g. separate fingers & toes  Caspases – any group of proteases that mediate by encoding a protease that degrades cell structures 2. Likelihood that modern multi-cellular life forms are monophyletic.  False, volvox genus is not monophyletic o 4 or 5 independent lines have proven multicellularity has evolved multiple times 3. Characteristics of Volvocine algae that make them a useful model system to study transition to multicellularity.  Cells easy to grow  Volvox and clamy shared a common ancestor 50 mya (relatively recent)  Single cell  group  spherical (cell associates with cell wall on outside)  multicellularity (specialize)  ECM (extracellular matrix) – transparent stuff that holds them 4. Relative structure/function of Chlamydomonas vs. Volvox cells.  Unicellular chlamydomonas  Volvox o Has to do everything o Transparent extracellular o Loses its flagella when it matrix (ECM) that holds sphere asexually divides o Many somatic cells and a few o A little developmental plasticity dozen of reproductive cells 5. General process of Volvox asexual reproduction; role of somatic vs gonidial cells.  Juvenile gonida divide into 16 undifferentiated cells  volvox mature by asymmetrical division  invert  ECM growth  juvenile hatch and parent somatic cell die  Asymmetrical division and differentiation of fate o Daughter cells not the same size o Big – gonida (reproductive)  Continue dividing  Lost flagella and eyespot o Small – somatic cell  Stop dividing  Program cell death  Gonida cells are outside of sphere o Flagella somatic cells are pointing inwards o Then it flips itself inside out (inversion) so flagella and eyespot and pointing out  Can respond to light and move  Grow by adding more ECM until the juveniles are ready to hatch 6. Genetic possible approaches to identifying genes relevant in rise/maintenance of multi-cellularity.  Volvox has more elaborate ECM than chlamy  Look at proteins they have that are different that will allow them to specialize  Gel electrophoresis, restriction endonuclease enzymes  Compare regulation of genes  Comparative genomic study of what genes multicellular vs unicellular have  Knock out genes and mutants or cut them out 7. Types of data or insight revealed by comparative genomic studies in Chlamydomonas vs. Volvox  No right answer  Volvox doesn’t rea
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