RESUMEN
A model for testing random molecular evolution is proposed. Randomness of recurrent mutation is defined based on isotropy and zero covariance among nucleotide sites. Assuming an equal rate of mutation for the bases A, T, G, and C, in both DNA strands, a mutational matrix of transformation A, T, G, and C with 6 parameters is developed. Under this model the equilibrium proportions (F) of the bases are FA = FT = (D + E)/[2(D + E + H + J)] and FG = FC = (H + J)/[2(D + E + H + J)], D, E, H, J being 4 of the 6 matrix parameters. Thus the expected (FA + FT)/(FG + FC) ratio can also be tested. If the average rate of mutation is 10(-8) per nucleotide site and cell replication, the equilibrium for every site, in most species, is reached in 10(8) years. Eight DNA segments from human, bacteria, fungus and insect genomes were chosen to test these proportions and their heterogeneity among coding and non coding subsegments. While FG was similar to FC as expected, FA was highly different from FT Huge heterogeneities were found between coding and non coding segments and among non coding segments. These results are a strong evidence for non randomness of molecular evolution
Asunto(s)
Humanos , Animales , ADN , Evolución Molecular , Mutación , NucleótidosRESUMEN
Puérperas normales ingresadas al Hospital Clínico de la Universidad de Chile, la mayoría de ellas pertenecientes a un estrato socio económico bajo, mostraron un progresivo descenso en los niveles plasmáticos de proteínas totales, albúmina, ß - globulina, IgA e IgM, así como un aumento en los niveles de *1- globulina. Esta tendencia fue observada durante el período de diciembre de 1982 a agosto de 1985, mostrando un patrón plasmático similar al descrito para la desnutrición humana. Los cambios observados en las inmunoglobulinas sugieren un diferente patrón entre aquellas que atraviesan la placenta, de aquellas que no lo hacen, manteniéndose en la madre sólo aquellas que cruzan la placenta