16 - Evolution of Multicellularity

Question 1

Identify the function of caspases.

Answer 1

• Caspase - a protease involed in programmed cell death
• it is the main executioner enzyme and it is coded by the cell death abnormal gene, CED-3
• They cleave essential proteins, leading to a controlled, but irreversible, biochemical cascade causing cell shrinkage, chromatin fragmentation and cell death.

Question 2

likelihood that modern multi-cellular life forms are monophyletic.

Answer 2

• Multicellular life is not monophylectic
• Monophyletic: describes a group of organisms that meets this criteria:
  
  • they share a common ancestor
  • all descendents of that ancestor are included
• multicellular organism have evolved multiple times through time.

Question 3

characteristics of Volvocine algae that make them a useful model system for studying the transition to multi-cellularity.

Answer 3

• The common ancestor of animals and plants are so far back that its hard to get a model to study, but the volvox and chlamy is much easier because their ansentor is not that far back.

Question 4

relative structure/function of Chlamydomonas vs. Volvox cells.

Answer 4

• Chlamydomonas are unicelular
  
  • they are made up of a nucleus, basal body, eyespot, pyrenoid, chloroplast, mitochondrion, ER, ribosomes, golgi bodies. ect.
• Volvox cells are multicellular
  
  • consists of a sphere of two to three thousand small, flagellated, chlamydomonas-like cells that provide the individual Volvox with the ability to move.

Question 5

general process of Volvox asexual reproduction; role of somatic vs gonidial cells.

Answer 5

• A dividing gonidial cell, between a and b there is asymmetric division,
• the daughters that are produced are not the same size, we are getting differentiation of fate,
• the big cells are going to be gonidial cells and the smaller cells are somatic cells.
• The Gonidial cells are on the outside and the flagella of these cells are inward, which makes itself flip inside out (inversion), which means that now the gonidia are in the inside like they are supposed to be.
• the Juvenille spheroids get bigger by adding ECM (extra cellular matrix) until they are big enough and they pop out of their parent cell. This is important for multi-cellularity

Question 6

genetic approaches to identifying genes relevant in rise/maintenance of multi-cellularity.

Answer 6

• We can look at the proteins in the ECM, Volvox has more elaborate ECM than chlamy
• We can compare the genome of chlamy and volvox
• Compare the regulation of DNA of diffeferent species
• Look at all multi and compare with uni species
• Mutant genes, study volvox that cannot be multicellular because of mutations

Question 7

types of data or insight revealed by comparative genomic studies in Chlamydomonas vs. Volvox

Answer 7

Question 8

types of data or insight revealed by mutation/rescue experiments in Volvox.

Answer 8

Question 9

difference between orthologous and paralogous genes.

Answer 9

• orthologue - genes were present in ancestor. This gene is the same in chlamy and volvox that does different things, has a different roll in each species. You might not need to evolve new genes to become multicellular.
• In chlamy there is a gene (paralogue) which is related(does the same thing but for different reasons), the regulations is different in each species, in chlamy this gene represses photosynthesis when in low light, in volvox it shuts off photosynthesis because developmental signals in volvox.

Question 10

types of genetic changes associated with multi-cellular growth in Volvox.

Answer 10