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Category Archives: Canary Islands

Lactose tolerance favors obesity

While the lactose tolerance allele may have some positive health effects, notably because milk is one of the few good dietary sources of calcium, it seems to correlate also with some negative effects, namely obesity.
Ricardo Almon et al., Association of the European Lactase Persistence Variant (LCT-13910 C>T Polymorphism) with Obesity in the Canary Islands. PLoS ONE 2012. Open access ··> LINK [doi:10.1371/journal.pone.0043978]
Canary Islands, in spite of its subtropical geography, is one of the regions of the European Union where milk is most consumed, at levels comparable to Scandinavia. 
Although there is a strong correlation between being lactose tolerant and milk consumption it is not fully clear yet if it is excess milk consumption what makes people obese or an unknown collateral effect of the European lactase persistence allele.
Interestingly the correlation, very strong, is only found for obesity and not for being overweight:

Fig. 1 – BMI classification by LCT genotypes (LP: n = 330; LNP: n = 221)

 

Canarians, NW Africans, Iberians, etc. from the viewpoint of autosomal DNA

This new paper has several points of interest: on one side it studies Canarians in some detail, on the other it compares NW Africans and Iberians (and others) in a way that I cannot recall being done previously. All through the use of autosomal markers (those that represent best overall ancestry, regardless of historical accidents of gender bias).

The overall comparison of Canarians, mainland NW Africans, Iberians and other European populations is probably easiest to appreciate in fig. 1:

FST-based multidimensional scaling plot
Avery similar graph is achieved with a different technique (PCA) in figure 2, with samples plotted individually. 
Some overlap between North Africa and Iberia can be appreciated, however, as the authors note, this is smaller that what could have been led to believe based on autosomal markers such as Y-DNA. The greater (9%) North African influence in the Western half of the peninsula in comparison to the Eastern half (2%), also apparent in autosomal markers, is confirmed here. 

Figure 3. STRUCTURE [K=2] results based on EuroAIMs.
[Note: EuroAIMs are one specific subset of autosomal markers, chosen because they vary a lot between populations. CAN and CBN are both Canarians but from different datasets].
The authors also noticed that, in spite of the appearance created by some mtDNA lineages and the historical evidence of slave trade, specially in the Canary Islands, no West African (YRI) influence could be detected:

Fig. S1


Different levels of persistence of Guanche blood
While it is clear that Castilian (Spanish) colonization of the Canary islands was very intense, there is still some very noticeable background of original Guanche blood (represented surely by the North African, green, component). There are important differences however among the various Canary Islands (table 2):
  • La Gomera retains by far the greatest apportion of Guanche blood, showing a 43% of North African affinity.
  • Fuerteventura, La Palma and El Hierro also retain important Guanche blood (20-22%).
  • Lanzarote (16%) and the larger islands of Tenerife (14%) and Gran Canaria (12%) seem the ones that have received the greatest Iberian input, however they still retain some aboriginal genetics as well.
The Canary Islands
The island of La Gomera is also the one to have retained best some of the ancestral Guanche customs, notably the whistling language known as Silbo Gomero.
See also: