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Lecture 16

Lecture 16 Evolutionary Multi-Cellularity.docx

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Biology 1002B
Tom Haffie

Lecture 16: Evolutionary Multi-Cellularity Wednesday, March 06, 2013 10:32 AM Today's Topics:  Announcements:  Homework: Lecture Topic:  Multi-cellularity = division of labor/death  Which cells are mortal/immortal  Epigenetic changes do not change the DNA sequence and are persistent (they stay beyond the particular event that causes the changes in the first place)  Regulation of gene expression affords the possibility of specialization  Genetic vs. epigenetic  Multi-cell evolved several times  Volvocine algae provide a productive model system  When chlamy wants to divide, it loses its flagella  Volvox is a transparent sphere with many somatic cells and a hand-full of reproductive cells  Not even volvox is monophyletic  Getting cells to cooperate with each other may not be as hard as imagined  Volvox embryology  From a to b, the cells seem to have differing sizes into somatic and gonidial cells  In continued division, the gonidial cells move to the outside of the embryo and stop dividing while the somatic cells continue to divide with their flagella on the inside  The embryo undergoes inversion, to flip themselves inside out so that the gonidial cells are on the inside  Juvenile and parental spheriods enlarge by accumulating ECM  Juveniles hatch and parental somatic cells die  Comparative Genimics  The genome of chlamy is not all that different from Volvox  Mutational studies identify important genes   Gls causes asymetric division  Lag shuts off somatic genes  Reg shuts off gonidial genes  The gene that allows volvox to divide
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