Download VGEC: Answer sheet

Simulating phase variation in Campylobacter
VGEC: Answer sheet
1a.)
No, you should have noticed that mutations occurred at
different times, and different combinations of genes
mutated to give different genotypes. There would have
been differences in the number of cells capable of
causing disease etc. This is because mutations are
completely random events, and different combinations
will be seen every time the simulator is run. This is
reflected in nature.
2a.)
The higher the mutation rate, the more cells capable of
taking up movement, and sticking to host cells.
2b.)
The population is more diverse at higher mutation rates.
Fewer cells with the original genotype and few blocks of
the same cells around each other.
3a.)
Mutations that occur early have more impact. This is
because mutations are passed down to descendant c
Simulating phase variation in Campylobacter
ells. The earlier this happens, the more likely the final
population is to reflect this.
3b.)
It is more likely that they will emerge from cells that
already have one mutation. They can emerge from cells
with zero mutations but this is unlikely. The different
genes are independent from each other and the chance
of all of them mutating at once is far higher!
3c.)
There will be variation in the number of times the
disease causing phenotype arises. This is because
bacteria do not mutate towards favourable genotypes,
they can just be selected for. This concept is also true
for antibiotic resistance, cells do not mutate in response
to antibiotics- resistant cells are just selected for by the
drug.
4a.)
RealisticThe simulator does display bacterial division, the
random nature of mutation is also highlighted in the
simulation. Genes do have different functions that can
interact and contribute to bacteria causing disease.
Unrealistic-
Simulating phase variation in Campylobacter
No selection (Disease would be favourable as it helps
them to multiply), there are many more phase variable
genes in real bacteria and their interactions are often
more complex. The mutation rates in the simulator are
too high and the bacterial populations are too small.
There is no simulation of environmental factors which in
real life would affect the speed of cell division.
4b.)
The cost and time consumption of simulations are low,
meaning you can do lots of repeats, generating lots of
data.
Key concepts conveyed by the activity Mutation is an entirely random process
o Cells do not mutate towards a favourable
genotype, the mutations are always there, they
can just be selected for.
 Mutations generate diversity in populations of
bacteria. Some of these mutations are preferable
and help bacteria to cause disease.