Concept 27 Mutations are changes in genetic information.

HI! Single nucleotide mutations in the mitochondrial (mt) control region are used as a molecular clock to measure human evolution. When two groups split off from a common ancestor, each accumulates different mutations. The number of mutations is proportional to the length of time that two groups have been separate. How many nucleotide differences are there between humans and chimps in this 379-nucleotide part of the mt control region? Click on nucleotide differences to highlight. 25 (That is incorrect. The total difference is the sum of different mutations that have occurred in each line.) 31 (That is incorrect. The total difference is the sum of different mutations that have occurred in each line.) 56 (That is correct.) 87 (That is incorrect.) So, 56 mutations have accumulated in this part of the mt control region since humans and chimps diverged from a common ancestor. Now let's look more closely at the human branch of the tree by comparing this part of the mt control region between two living (modern) humans. How many nucleotide differences have accumulated in this 379-nucleotide part of the control region? 3 (That is incorrect. The total difference is the sum of different mutations that have occurred in each line.) 4 (That is incorrect. The total difference is the sum of different mutations that have occurred in each line.) 7 (That is correct.) 10 (That is incorrect.) Seven is, in fact, the average number of mutations in this region between any two people from populations around the world. This number of differences has been calibrated to equal about 150,000 years. Thus, mitochondrial DNA analysis suggests that all living (modern) humans share a common ancestor who lived about 150,000 years ago. 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 ancient member of the human genus Homo and lived in Europe from about 300,000 years ago, until it became extinct about 30,000 years ago. Clearly, during part of its span on earth, Neandertal shared its European habitat with Cro Magnon, the direct ancestor of modern humans (Homo sapiens). There has long been controversy about whether Neandertal was the direct ancestor of modern Europeans or a "dead-end" in hominid evolution. Which diagram shows Neandertal as an ancestor of modern humans? Neither (That is incorrect.) A (That is incorrect.) B (That is correct.) Both (That is incorrect.) In 1997 Svante Paabo's group at the University of Munich provided an answer to this question by analyzing mitochondrial (mt) DNA that they extracted from a Neandertal bone. The following is a sequence alignment between a part of the mt control region of Neandertal and a modern human. How many mutation differences are there in the 379-nucleotide region? 5 (That is incorrect.) 8 (That is incorrect.) 19 (That is incorrect.) 28 (That is correct.) If, as discussed earlier, 7 mutations equal 150,000 years on the mitochondrial clock, how many years do 28 mutations equal? 50,000 years (That is incorrect.) 300,000 years (That is incorrect.) 600,000 years (That is correct.) 900,000 years (That is incorrect.) Svante Paabo's data are consistent with which of the two diagrams showing the relationship between Neandertal and modern humans? Remember, modern humans descended from a common ancestor 150,000 years ago. Neither (That is incorrect.) A (That is incorrect.) B (That is correct.) Both (That is incorrect.) Neandertal and humans diverged 450,000 years before the common ancestor of all modern humans, so it is very unlikely that Neandertal is closely related to any group of modern humans. According to mt DNA analysis, Neandertal is on a separate branch. CONGRATULATIONS! YOU'RE SO SMART!