Chemistry Reference
In-Depth Information
Figure 6.1a.
Worldwide distribution of frequency of lactase persistence. Dark grey indicates
the proportion of lactose digesters (presumed lactase persistent) in a given population and light
grey represents maldigesters (presumed non-persistent). A central circle indicates that the overall
frequency for that country is comprised of different ethnic groups with very different phenotype
frequencies. For examples of these cases, see Figure 6.1b. (Data taken from Bloom and Sherman,
2005; Mulcare, 2006)
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Sudan
Nigeria
Middle East
Figure 6.1b.
Examples of countries in which individual ethnic groups display large differences
in lactose absorption capacity.
(Swallow and Hollox, 1999). These frequencies reveal clearly that lactose intol-
erance is the most commonly observed phenotype in humans, with lactase
persistence being common only in those populations with a long history of
pastoralism and where milking has been practised. Lactase persistence is at
highest frequency in north-western Europe, with a decreasing cline to the south
