Y chromosomes and mtDNA of Sweden

It's interesting to see a study of the current population of a country. If one is interested in deep pre-historical origins, one must ensure that his sample has no known foreign ancestry among the lines of interest. But, if one is interested in the current and future course of the population, then the totality of the population must be sampled.

This is a good opportunity to track shifting gene frequencies due to immigration and/or differential fertility. It would be a good idea for countries to start spending some money on a genetic census of their population. This would not need to involve all the inhabitants, and could be carried out for the fraction of cost that governments pay to collect all sorts of other statistics. Such a census would provide an important source of data to future scientists investigating the demography of Europe during this transitional era.

From the paper:

Several haplogroups had interesting frequency patterns, but also wide confidence intervals, necessitating caution in the interpretations. The mtDNA haplogroup with the strongest geographical cline, U5b, is known to have high frequencies among the northern Saami population, consistent with our results (Tambets et al. 2004). The high frequency of the Y-chromosomal R1b in the south, observed also by Karlsson et al. 2006; is consistent with its abundance in Central Europe and Denmark (Semino et al. 2000; Brion et al. 2005). Haplogroup R1a1 is more common in Norway than in Sweden (Dupuy et al. 2006), and its high frequency in Värmland/Dalarna and Halland supports the historically plausible connection to Norway (Lindqvist, 2006). Y-chromosomal haplogroup N3 (Lappalainen et al. 2006) and mtDNA haplogroup H1f (Loogväli et al. 2004; Lappalainen et al. 2008) are common in Finland, and had increased frequencies in several Swedish counties with historical ties to Finland: Eastern Svealand was the most important destination of the Finnish immigration wave in the 1970's; in Norrland the Finnish influences date back to ancient times and in Dalarna to the 17th century (Pitkänen 1994).

When compared to previous knowledge of ethnic Swedes without immigration in their familial background (Lappalainen et al. 2008), the frequencies of several haplogroups showed effects of 20th century immigration from more distant countries. The Y-chromosomal I1a had decreased frequencies in Malmö and Gothenburg most probably due to replacement by haplogroups that are common among immigrants. African immigration contributes to the frequencies of mtDNA haplogroups L3*(xN,M) and L* (xL3) (Chen et al. 2000), and Y-chromosomal haplogroup A (Underhill et al. 2001; Jobling & Tyler-Smith 2003), while Near Eastern influence can be seen in mtDNA haplogroup U7 and possibly J (Richards et al. 2000; Abu-Amero et al. 2007; Achilli et al. 2007). Asian and American immigration can be observed in the slightly elevated frequencies of mtDNA haplogroups M, A, C, D and G (Quintana-Murci et al. 2004; Hill et al. 2007) and the Y-chromosomal O, K* and P* (Underhill et al. 2001; Jobling & Tyler-Smith 2003). The frequency of the Y-chromosomal haplogroup I1b may associate to immigrants from Balkan and Eastern Europe (Rootsi et al. 2004). In Malmö and Gothenburg immigration was the main contributor to their isolated positions in the Y-chromosomal PCA plot and probably also to the higher diversities compared to the surrounding populations. These phenomena were not observed in Stockholm, where most of the immigrants come from Finland (Statistics Sweden, http://www.scb.se).

Annals of Human Genetics doi: 10.1111/j.1469-1809.2008.00487.x

Population Structure in Contemporary Sweden—A Y-Chromosomal and Mitochondrial DNA Analysis

T. Lappalainen et al.

Abstract

A population sample representing the current Swedish population was analysed for maternally and paternally inherited markers with the aim of characterizing genetic variation and population structure. The sample set of 820 females and 883 males were extracted and amplified from Guthrie cards of all the children born in Sweden during one week in 2003. 14 Y-chromosomal and 34 mitochondrial DNA SNPs were genotyped. The haplogroup frequencies of the counties closest to Finland, Norway, Denmark and the Saami region in the north exhibited similarities to the neighbouring populations, resulting from the formation of the Swedish nation during the past millennium. Moreover, the recent immigration waves of the 20th century are visible in haplogroup frequencies, and have led to increased diversity and divergence of the major cities. Signs of genetic drift can be detected in several counties in northern as well as in southern Sweden. With the exception of the most drifted subpopulations, the population structure in Sweden appears mostly clinal. In conclusion, our study yielded valuable information of the structure of the Swedish population, and demonstrated the usefulness of biobanks as a source of population genetic research. Our sampling strategy, nonselective on the current population rather than stratified according to ancestry, is informative for capturing the contemporary variation in the increasingly panmictic populations of the world.

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