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Genetic approaches to understanding human adaptation to altitude in the Andes

J. L. Rupert^1,* and P. W. Hochachka²

¹ Department of Pathology and Laboratory Medicine and
² Department of Zoology, The University of British Columbia, Vancouver, Canada V6T 2B5

View larger version (28K): [in a new window]   Fig. 1. South America and the central region of the Andes (inset). The shaded area in B represents the approximate extent of the Andes and includes the altiplano region. The locations of some of the research sites mentioned in the text are indicated.

View larger version (23K): [in a new window]   Fig. 2. Predicted change in allele frequencies in a bi-allelic system over the duration of human occupation of the Andes (approximately 12000 years or 600 generations) assuming that the relative fitness of genotype AA is 0.5%, 1.0% or 2.0% greater than that of genotype aa. The initial frequency of allele A is 5% in all cases. Predictions were made using the population simulation program PopBio 2.4 (Bowman and The Reed Institute, 1995) and assume co-dominance (heterozygotes have an intermediate fitness) and random breeding in an unlimited population.

View larger version (16K): [in a new window]   Fig. 3. Examples of broad-based heritabilities (H2) for various traits in humans (adapted from Hartl, 2000).

View larger version (22K): [in a new window]   Fig. 4. Stature-adjusted mean lung function in 203 male (M) and 166 female (F) Aymara for the darkest and lightest skin reflectance tercile categories. An asterisk denotes a significant difference between categories (P<0.01). TLC, total lung capacity; VC, vital capacity; FEV, forced expiratory volume; RV, residual volume; IC, inspiratory capacity; ERV, expiratory reserve volume. The figure is based on data presented by Greksa (Greksa, 1996).

View larger version (14K): [in a new window]   Fig. 5. Origins of linkage disequilibrium. In this example, there are two linked genes, A and B, one of which (A) has a bi-allelic polymorphism (A and A1). A germline mutation occurs in gene B, creating allele B1 (bold) in an individual who is heterozygous at gene A. The offspring of this individual have to inherit the haplotypes AB or A1B1 from this parent unless the two alleles are separated by a crossover, the chance of which is approximately 1% for every million bases separating the two genes. If no crossover ever occurs, then the descendant population (DP1) will consist of only three of the possible four allele combinations, and B1 would always be associated with A1 (A1B having come from a different ancestor). The reciprocal, however, would not be the case (i.e. A1 would not always be associated with B1). In DP1, alleles at A and B would be observed to be in linkage disequilibrium because the frequencies of allele combinations would not equal the product of their frequencies, as would be expected if the four alleles were assorting independently. If there has been some recombination, a new haplotype AB1 would appear in the population (DP2). If this was a rare and/or recent event, the new haplotype would still be less common than predicted and the alleles would still be in linkage disequilibrium. The rate at which linkage disequilibrium will decay depends on the recombination fraction

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