Thursday, November 15, 2012

Multipath

Multipath signalling in a communication system is a propagation phenomenon where a signal propagates by multiple paths from sender to receiver.  As the signal travels through the media in each path, it experiences destructive and constructive interference and phase shifting.

Successfully communicated multipath signals at the receiver are usually redundant.  If not, they would likely not survive negative impacts of multipath such as fading and could not be reconstructed into a comprehensible format at the receiver.

A possible analogy in population genetics can be drawn when a population splits into two or more separated, isolated populations.  Over time, these separated populations undergo positive and negative selection as well as diffusion.  When the separated populations encounter each other again, and are measured, it is possible to misinterpret the underlying structure of the reconstructed population if the measurement system cannot model multipath effects.

Another analogy can be drawn with respect to redundancy.  The genome seems to have high redundancy.  Recent examples of this are the finding of the development of lactase persistence in Europeans and East Africans and the development of high altitude adaptation in Tibetans and Ethiopians on different loci.

(Update November 19th:  It occured to me that some might take this communication system analogy as an argument for intelligent design.  The analogy is not meant as an argument for Intelligent Design. Rather, it is meant to suggest that some ideas from formal communication theory may be illustrative in population genetics.  I mentioned the seminal communication theory paper by Claude Shannon in the last post, MULTIMIX.  Here's the link again:  A Mathematical Theory of Communication, Claude Shannon, The Bell System Technical Journal, 1948.)


Related papers:

The genetic architecture of adaptations to high altitude in Ethiopia
Alkorta-Aranburu et al.
preprint
http://arxiv.org/abs/1211.3053

The Origins of Lactase Persistence in Europe
Yuval Itan et al.
PLoS Comput Biol 5(8): e1000491. doi:10.1371/journal.pcbi.1000491
(link)

Genetic Evidence for High-Altitude Adaptation in Tibet
Tatum S. Simonson et al.
Science Vol. 329. no. 5987, pp. 75 - 78
DOI: 10.1126/science.1190371
(link)

Convergent adaptation of lactase persistence in Africa and Europe
Tishkoff et al.
Nature Genetics 39, 31 - 40 (2007)
Published online: 10 December 2006 | doi:10.1038/ng1946
(link)

3 comments:

  1. Not sure if multipath is a good analogy, specially when convergent evolution is a well studied phenomenon - that for some odd reason you don't even mention.

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  3. I'm just tring to suggest on an intuitive level that if you have a species that is diverse, with pockets of refugia populations at every ice age, who then become highly mobile and possibly reconverge during interglacials, there is likely a high need to evolve new traits within each of these populations and at each climate shift step. The ability to generate these new traits likely demands redundancy of loci of opportunity of some form.

    At the same time, the flip side of this is the ability to retain key long term traits even after repeated up and down selection processes under a refugia and range shift scenario.

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