Wednesday, July 06, 2005

Some Interesting Items About Genetics

First up is this article about the relationship between ancient Taiwanese and Polynesian populations. Researchers looked at the mitchondrial DNA of Taiwanes, Chinese, Polynesian and other southeast Asian populations. They compared mtDNA markers and concluded that Polynesians are descended from indigenous Taiwanese populations some 10,000-20,000 years ago.

Then we have an article at PLOS Biology that examined the poepling of the Americas using a modified "Isolation with Migration" model.

Taken together, the analyses in this study suggest a recent founding of the New World Amerind-speaking peoples by a small population of effective size near 70, followed by population growth in the New World. It is interesting that the analyses do not suggest much population size change in Asia since the time of the founding of the New World population.

Additional results suggest that this occured around 20,000 years ago (however, see my post on the footpring found in Mexico below).

Which brings us to this article concerning the evolution of the Alu elements in the human genome. Basically, Alu elements are a form of transposable DNA (similar to tandem repeats and microsatellite DNA). Alu elements are capable of repeating, via a RNA intermediate, themselves throughout the DNA (which is why the are called retrotransposable - other types don't require the use of an RNA intermediate). From the article:

Batzer's team demonstrated that the AluYb linage dates back approximately 18-25 million years. Their results also indicated that the AluYb sub-family underwent a major species-specific expansion in the human genome during the past 3-4 million years. This apparent 20-million-year stretch of general inactivity, followed by a sudden outburst of human-specific retrotransposition activity in the past few million years, led Batzer and colleagues to formulate a new theory for the evolution of Alu elements, termed the "stealth driver" model. In the "stealth driver" model, low-activity Alu elements are maintained in low-copy number for long periods of time and occasionally produce short-lived hyperactive progeny that contribute to the formation and expansion of Alu elements in the human genome.

Which leads to the following article Does antibiotic use in agriculture have a greater impact than hospital use?.

The authors in this study were interested in how anti-biotic resistent bacteria moved from animals to humans.

Despite the evidence linking bacterial antibiotic resistance on farms to resistance in humans, the impact of agricultural antibiotic use remains controversial [16–19] and poorly quantified. This is partly because of the complex of population-level processes underlying the between-species (“heterospecific”) and within-species, host-to-host (“horizontal”) spread of ARB. To emerge as human pathogens, new strains of ARB must (1) evolve, originating from mutations or gene transfer; (2) spread, usually horizontally among humans or animals, but occasionally heterospecifically; and (3) cause disease.

The emergence of a new type of resistance is a highly random event, which can't be predicted accurately, and may involve multiple steps that preclude perfect understanding even after the fact. Spread is equally complicated and may obscure the origins of resistance. In some cases, emergence of resistance in one bacterial species is a consequence of the emergence and spread in another species, followed by the transfer of resistance genes from one bacterial species to another.

This is one article everyone should read.

Finally, Trees, Vines And Nets -- Microbial Evolution Changes Its Face discusses the horizonatl transfer of genes in microbial evolution. The link to the previous article:

A few species, including beneficial nitrogen-fixing soil bacteria, appear to be 'champions'of horizontal gene transfer; "it's entirely possible that apparently harmless organisms are quietly spreading antibiotic resistance under our feet,"