Genetic studies performed on heterogeneous populations make identifying rare variants for complex diseases difficult because of confounding variables associated with heterogeneous populations. This study collected genetic samples and medical information for 1803 people within a relatively isolated population. The authors report that analysis of the isolated population reveals significant heritability of medically relevant traits that might not have otherwise been uncovered with a more heterogeneous cohort.
Sunday, October 25, 2009
Human genetic variation extends beyond differences in the underlying genetic sequence. A recent study reported in Nature provides a more robust understanding of DNA cytosine methylation, an alternate source of genetic variation. While DNA methylation was primarily associated with repeat CpG (Cytosine-phosphate-Guanine) rich portions of the genome, Lister et al. report that approximately 25% of methylation in embryonic stem cells occurs in non CpG portions of the genomes. CpG regions are associated with promoter regions of genes, and methylation of these regions are thought to regulate gene expression. The report of methylation in non CpG regions raises new questions about the role of this epigenetic modification. The publication also represents one of the first papers describing a relatively complete map of the human epigenome.
Saturday, October 24, 2009
Monday, October 19, 2009
Humans are widely thought to have expanded out Africa starting approximately 50,000 years ago. In this process, genetic variation was reduced the further populations moved away from Africa due to successive bottleneck events. The frequency and nature of these bottleneck events have already been extensively explored in the literature. A recent study, which analyzed 783 microsatellite loci genotyped on 53 globally representative populations, concludes that two major bottleneck events occurred in human history – the first occurring as humans moved out of Africa and the second as humans moved across the Bering Strait into the New World. These events can be detected due to the genetic implications of bottleneck events. After sharp declines in population numbers, excess heterozygosity exists in the population than would be expected given the number of alleles remaining. The authors used the program ‘Bottleneck’ to detect this signature. This study reconfirms the conventional understanding of human expansion.