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Lecture 16

Biology 1002B Lecture Notes - Lecture 16: Comparative Genomics, Chloroplast, Xist (Gene)

Course Code
BIOL 1002B
Tom Haffie

of 4
Lecture 16: Evolutionary Multi-Cellularity
Wednesday, March 06, 2013
10:32 AM
Today's Topics:
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 asymmetrically is also in chlamy, but chlamy doesn't
divide asymmetrically
They probably had a common ancestor but now the same gene has different jobs in two
different orgs
regA is a transcription repressor of nuclear chloroplast genes
If you stop cells from making new chloroplast pns, the chloroplast will eventually shut
down and the cell will not be able to reproduce
In chlamy, there is a gene that is called a paralogue (a gene that has duplicated in
common ancestor but now has different functions/regulations in new orgs - in chlamy it
shuts down photosynthesis in low light, in volvox the gene is used to shut down
photosynthesis as a developmental cue)
invA is in chlamy as well
After class, use this space to summarize the main points of this Lecture Topic.
Acetylation of histones
Gene silencing
Study Questions
After the lecture, create questions based on the notes.
Which of the following regulation mechanisms is not "epigenetic"
1. DNA methylation
2. Histone acetylation
3. Binding of Xist RNA
4. Binding of lac repressor
What kind of study would help to identify the genes that are important for multi-cellularity
Compare the pn in ECM
Compare the DNA of orgs
Compare the regulation of genes in diff species
Comparative genomics with orgs that should be able to do stuff, but for some reason can't
In what way would you predict that the volvox genome is different from chlamy
1. More DNA