Are Chinese descendants of an African Eve?
0 
DNA molecules point to a startling conclusion
Jin chose the Y-chromosome because it is relatively pure from a genetic perspective. Human beings have two sets of chromosomes, X and Y, inherited from our mothers and fathers respectively. The Y-chromosome comes from male and has a low mutation rate. It reflects how human genes are passed on from generation to generation more clearly than the X chromosome. As a result, geneticists see it as ideal material for the study of human origins.
Jin and his team focused on three SNPs on the Y-chromosome – M89, M130 and YAP. They are mutations of another mutated DNA molecule M168, which originated in Africa between 31,000 and 79,000 years ago.
"M168 originated only in East Africans. All people outside Africa and some Africans still have it. So it is the most direct evidence to prove that modern humans came from Africa." Jin wrote in his paper.
How do scientists work out the age of strand of DNA?
You may ask: How do scientists work out the age of a DNA component? How do scientists know M168 existed in ancient Africa? How do they work out exactly when it originated?
Associate Professor Li Hui said that non-genic DNA sequences are used in molecular anthropology because genes possess many physiological functions. If a gene mutates, a person's health may be greatly affected.
There are two fundamental features of the materials Jin and his team chose: they were non-genic and genetic haploid. Mitochondrial DNA and Y-chromosomes belong to this category. Most of the Y-chromosome consists of non-genic sequences. The team analyzed two types of mutation of the non-genic sequence. The first was SNP. This type of mutation is rare and stable. It will not repeat or change back to its original form. The structural relationships of all types of Y-chromosome all over the world are based on this feature. The other type of mutation was short tandem repeats (STR). These lengthen and shorten at a constant speed. Thus the origin of each type of Y chromosome can be dated by dividing the total number of mutations by the rate of mutation.
In other words analysis of SNP and SRT mutations show when the M168 mutation occurred.
DNA from modern Chinese proves their African origins
Jin Li and his team randomly selected 9,988 Chinese males as samples. They found that all samples of M89, M130, and YAP led to only three mutations. 9,329 samples (93.4 percent) mutated into M89T、M130C and YAP-; 370 samples (3.7 percent) mutated into M89C、M130T and YAP-. 290 samples (2.9 percent) mutated into M89C、M130C and YAP+. No new mutation was found. The results coincided with findings in other parts of the world, that is, M168 displayed no new mutations in China. The result proved that Chinese people must have come from Africa, along with all other modern humans. But Jin Li's research also supported the African origin theory from another perspective, which was beyond their original expectations.
Go to Forum >>0 Comments