E X E R C I S E S
II. Using mt Sequences to Test Models of Human Evolution
1. Since their initial discovery in the Neander Valley of Germany in 1856, the heavy-set bones of Neandertal have fascinated scientists, as well as the general public. Neandertal was an archaic member of the genus Homo, which lived in Europe beginning about 300,000 years ago and became extinct about 30,000 years ago. Clearly, during part of its span on earth, Neandertal shared its European habitat with modern humans (Homo sapiens). There has long been controversy about whether or not Neandertal was the direct ancestor of modern humans. Alternatively, if Neandertal and Homo sapiens were separate, was there any significant exchange of genes between the two populations?
According to the multiregional model, modern humans developed concurrently from several different archaic populations living in different parts of the world. Under this model, Neandertal was the ancestor of modern Europeans, while Java man (Homo erectus) was the ancestor of modern Asians.
According to the displacement model, better know as "Out of Africa," Homo sapiens arose from a single founding population that emerged from Africa in the last 100,000-200,000 years. This group migrated successively to Europe and Asia, displacing archaic hominids.
In 1997, an international research team headed by Svante Paabo, extracted DNA from the humerus of the original Neandertal specimen, amplified the sample by PCR, and cloned the resulting products in E. coli. The cloned fragments were then used to reconstruct a 379-bp stretch of the mt control region. Now, you will use the DNA Sequence Server at the DNA Learning Center WWW site to recreate this study and answer the questions posed above. You will obtain mt control region sequences from several sources and then move them onto the analysis workspace of the DNA Sequence Server Page.
2. The number of differences in mt sequence provides a measure of the genetic distance between populations – that is the amount of time that has elapsed diverged from a common ancestor. Before one can use mt mutations as a "molecular clock," one must set the clock by some reference. The reference for hominid evolution is the estimated divergence between humans and chimpanzees 4 million years ago.
In order to check your conclusions, visit again the Theory chapter and the 'Neandertal Mystery' in the Media/Animation chapters.
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