miércoles, junio 11, 2008

Looking for Darwin in all the wrong places

Looking for Darwin in all the wrong places: the misguided quest for positive selection at the nucleotide sequence level

AL Hughes

Heredity (2007) 99, 364–373

Recent years have seen an explosion of interest in evidence for positive Darwinian selection at the molecular level. This quest has been hampered by the use of statistical methods that fail adequately to rule out alternative hypotheses, particularly the relaxation of purifying selection and the effects of population bottlenecks, during which the effectiveness of purifying selection is reduced. A further problem has been the assumption that positive selection will generally involve repeated amino-acid changes to a single protein. This model was derived from the case of the vertebrate major histocompatibility complex (MHC), but the MHC proteins are unusual in being involved in protein–protein recognition and in a co-evolutionary process of pathogens. There is no reason to suppose that repeated amino-acid changes to a single protein are involved in selectively advantageous phenotypes in general. Rather adaptive phenotypes are much more likely to result from other causes, including single amino-acid changes; deletion or silencing of genes or changes in the pattern of gene expression.

Heredity (2007) 99, 364–373; doi:10.1038/sj.hdy.6801031;
published online 11 July 2007

Podrán encontrar el pdf en el grupo yahoo...

4 comentarios:

Chico dijo...

Buena! Es un punto importante, pero dificil de criticar. Mucho barroquismo tecnico. M. Lynch hace una critica similar:

The frailty of adaptive hypotheses for the origins of organismal complexity

http://www.pnas.org/cgi/content/abstract/0702207104v1

cristian G. dijo...

me parece estupendo, casi todo los ejemplos de seleccion positiva quedan descartados. ademas hace notar lo que a nadie mas le parece importar y es que los casos donde mutaciones afectan fenotipos son muy escasos. y generalmente asociados con pigmentacion, que es uno de los pocos fenotipos directamente asociado a una proteina.

Chico dijo...

Es raro que al buscar seleción positiva en mutaciones pontuales se olvidan que las clases del MHC se originaran por grandes duplicaciones, quizá duplicaciones cromosomales o genomicas; que el MHC se origin[o de una chaperona; que RAG1 y RAG2 (recombinase activating gene) son de origen retroviral, etc. Gustavo: que tal un post sobre el tema?

Sanders dijo...

"statistical methods that fail adequately to rule out alternative hypotheses, particularly the relaxation of purifying selection"

Precisamente lo que confundieron con selección positiva, en el caso de los sticklebacks fósiles...