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)
Lost flagella and eyespot
o Small – somatic cell
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