Human populations are heterogeneous in terms of susceptibility to particular diseases or responses to therapeutic interventions, and understanding genetic variations between humans has been a key issue in biomedical research. In 16 August Science, Yan et Johns Hopkins Medical Institutions, Baltimore, USA, present a method for assessing differences in allele expression levels, which may account for many human variations (Science 2002, 297:1143).

Yan et al. developed a fluorescent dideoxy terminator-based method, which can identify expression differences of 20% (and more) between two alleles in a heterozygous individual. Individuals in a pool of 96 who were heterozygous for any of 13 selected genes were analysed, and significant differences in allelic variation were found in six of the 13 genes, with transcript ratios varying from 1.3:1.0 to 4.3:1.0. For example, three of 27 individuals heterozygous for the Calpain-10 gene showed allelic variations in the expression of this...

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