Comments for the week

A few things to run through for the week on mock and evol:

Mock:
(esp to Jane)
Absorbency is not the equivalent of wavelength. It is more related to intensity.

But let's us examine what is intensity first -a greater intensity of light means having more photons (increased conc) to strike a surface.
Compare this with wavelength - the wavelength of light will determine the amount of energy the photons will carry.
Therefore, having a higher intensity of light at a particular wavelength means having more photons of a particular energy.
How is this related to absorbancy?

The maximum absorbance of a plant is determined by the photosynthetic pigments it contains. If you shine blue light at it, how much of the energy can it absorb? If you start at low intensity, the plant can probably photosynthesize more if you increase intensity until other limiting factor comes into play.
you may ask: but didnt we fix the intensity of the light?
Yup you did but a plant will have difficult capacity to absorb different colored light (diff wavelength). For green color , you may need x photons to reach max, but for blue you may need 10x photons to hit its max so while the intensity of the light has been fixed, the effect on the rate of photosynthesis due to diff colored light will differ and each of them has it own max absorbance before other limiting factor comes to play. So if intensity is not high enough, you may give same rate of photosynthesis for different colored light because one may have reached its max while the other has not.

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Evol

The story of marsupial. It was once thought (and perhaps still so) that marsupials are the ancestors of placental mammals but evidence is emerging to suggest that these two groups branch off at about the same time.
But they are still deliberating on why Marsupial are found in high conc in Australia: the drift? different selection pressure? or both?


http://www.ucmp.berkeley.edu/mammal/marsupial/marsupial.html

http://en.wikipedia.org/wiki/Marsupial

http://bcb705.blogspot.com/2006/05/continental-drift-marsupials-and.html


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a few highlights we have learnt from Evol - just to clarify:

1) there is something called the species-area relationship: in short, when you looked a group of islands, you have to consider the size of it and the distance it is from the main island to predict variety of species

2) For neutral mutations, the key is really having no effect on fitness
For a mutation that leads to no change in phenotype, it is definitely neutral since there would not be a change in fitness either.
But mutations that do affect phenotype in measurable ways but do not affect the organism's fitness should also be considered as neutral.
It is definitely reasonable to do so because that will account for variants we see in our population due to spontaneous mutation. But we will consider it as a minor for now.

We often work with "no change in phenotype' as in the notes because that was what Kimura first proposed and most probable since it is considerably rare to have a change in phenotype without affecting fitness - although not impossible.


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Reiterate:
Evo MCQs Part 2.

32: (A) - bcos the question compared "btw" population. each population will see an increased in genetic variation but btw population, there is less distinction since they each now shared certain common alleles/genes.

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A question came to mind by alicia some time back:

How does membrane-bound AChE hydrolyse ACh? How can persistent signaling be achieved?
If they are membrane-bound, how do they hydrolyse ACh? If all ligand-receptor interaction is transient, how can there be persistent signaling?

The binding of ligand and receptor is indeed transient. What AChE offer to do is to hydrolyse free ACh so that the concentration of ACh in synaptic cleft increases for an increased probability of binding of the ligand to receptor and thus an observed substained signaling (the reversible reaction is less likely to go backward yah?) Persistence in signal does not refer to a tighter binding but increased probability/prolonged of so.