New MBE: Click languages, human-specific genes, mtDNA, selection & non-coding DNA
The latest Molecular Biology and Evolution looks like a cracker & I'm going to cherry pick some of the more interesting papers from Henry's point-of-view.
The first one to jump out at me (and Michael who prodded me to post this) is History of Click-Speaking Populations of Africa Inferred from mtDNA and Y Chromosome Genetic Variation (open access):
Little is known about the history of click-speaking populations in Africa. Prior genetic studies revealed that the click-speaking Hadza of eastern Africa are as distantly related to click speakers of southern Africa as are most other African populations.The Sandawe, who currently live within 150 km of the Hadza, are the only other population in eastern Africa whose language has been classified as part of the Khoisan language family. Linguists disagree on whether there is any detectable relationship between the Hadza and Sandawe click languages. We characterized both mtDNA and Y chromosome variation of the Sandawe, Hadza, and neighboring Tanzanian populations.
New genetic data show that the Sandawe and southern African click speakers share rare mtDNA and Y chromosome haplogroups; however, common ancestry of the 2 populations dates back >35,000 years. These data also indicate that common ancestry of the Hadza and Sandawe populations dates back >15,000 years. These findings suggest that at the time of the spread of agriculture and pastoralism, the click-speaking populations were already isolated from one another and are consistent with relatively deep linguistic divergence among the respective click languages.
Some of Arndt von Haeseler's team have explored the human genome in Mapping Human Genetic History, with a rather striking finding that about one third of human genes started to evolve prior to the human/chimp/gorilla divergence. I'll let their abstract explain:
The human genome is a mosaic with respect to its evolutionary history. Based on a phylogenetic analysis of 23,210 DNA sequence alignments from human, chimpanzee, gorilla, orangutan, and rhesus, we present a map of human genetic ancestry. For about 23% of our genome, we share no immediate genetic ancestry with our closest living relative, the chimpanzee. This encompasses genes and exons to the same extent as intergenic regions.We conclude that about 1/3 of our genes started to evolve as human-specific lineages before the differentiation of human, chimps, and gorillas took place. This explains recurrent findings of very old human-specific morphological traits in the fossils record, which predate the recent emergence of the human species about 5-6 MYA. Furthermore, the sorting of such ancestral phenotypic polymorphisms in subsequent speciation events provides a parsimonious explanation why evolutionary derived characteristics are shared among species that are not each other's closest relatives.
Next, A Long-Term Evolutionary Pressure on the Amount of Noncoding DNA, which explores in silico (=simulates) how DNA accumulates non-coding regions (sometimes called "junk" DNA). The abstract says that their results show:
...(Under) low mutation rates, the indirect selection of variability promotes the accumulation of noncoding sequences: Even in the absence of self-replicating elements and mutational bias, noncoding sequences constituted an important fraction of the evolved genome because the indirectly selected genomes were those that were variable enough to discover beneficial mutations.On the other hand, high mutation rates lead to compact genomes, much like the viral ones, although no selective cost of genome size was applied: The indirectly selected genomes were those that were small enough for the genetic information to be reliably transmitted. Thus, the spontaneous evolution of the amount of noncoding DNA strongly depends on the mutation rate.
Our results suggest the existence of an additional pressure on the amount of noncoding DNA, namely the indirect selection of an appropriate trade-off between the fidelity of the transmission of the genetic information and the exploration of the mutational neighborhood. Interestingly, this trade-off resulted robustly in the accumulation of noncoding DNA so that the best individual leaves one offspring without mutation (or only neutral ones) per generation.
Finally, Relative Rates of Evolution in the Coding and Control Regions of African mtDNAs who explore the substitution rates of synonymous and non-synonymous sites in human mtDNA. They show that there appears to be strong bias towards synonymous mutations in the coding region, suggestive of purifying selection. Their analysis also shows that around 3% of the total sites are changing faster than the expected neutral rate, sometimes by more than an order of magnitude. This may be indicative of positive selection at those loci.
Technorati Tags: genetics, click languages, mtDNA,
March 22nd, 2008 - 09:46
Human-Specific Genes: Apparently there are 50-100 genes that have no counterparts in other species. Despite the probability that these genes are quite important to our species, little is known about them.
Now scientists at Washington University School of Medicine in St. Louis have produced the first detailed analysis of the cellular functions of a hominoid-only gene, TBC1D3. They affirmed earlier evidence linking the gene to cancer, showing that TBC1D3’s protein can keep cellular growth factors active and helps turn on RAS, a protein that is active in a third of all human cancers.
Orangutans, Human-animal embryos
Using hybrid human-animal embryos for experiments has been attacked viciously by the Catholic Church, despite the fact that these are not going to be used to give birth to a chimera.
As a matter of curiousity human/primate chimera’s should be possible. And I came across a news item where a woman was raped by a “pet” orangutan.