Question

2. You are a primatologist interested in human evolutionary history. On a recent expedition to Africa, you discover a new species of great ape, similar to a Gorilla. You are interested in estimating how long ago your new species shared a common ancestor with gorillas. You decide to use a molecular clock, based on the Ψη-globin pseudogene nucleotide sequence. Based on fossil evidence, you know that Humans and Chimps shared a common ancestor about 6.6 million years ago, so you can use these two species to calibrate your clock. You sequence this gene from blood samples of your species and obtain homologous sequences from (Genus): Humans (Homo), Chimpanzees (Pan), and Gorillas (Gorilla). You find that Humans and Chimps share A nucleotides out of the 10000 in your sequence. Gorillas and your new species differ by only B out of 10000 nucleotides in the sequence (see values of A and B below). A) First, use the human and chimp data to calibrate your molecular clock by calculating the average rate of substitution between humans and chimps per site per year (L). Carry out all calculations to 5 significant digits! (3 points) B) Second, use your calculated substitution rate and the data on gorillas and your new species to estimate the time of divergence between gorillas and your new species. (3 points) C) You are pleased at your results but you know that your colleagues will want a more rigorous calculation. So you go back and sequence the same 10000 nucleotides from other primates for which you already know divergence dates from the groups already used above (e.g., Orangutans, Rhesus monkeys, and Spider Monkeys), using fossil evidence. What should you do next, and why are you going through all this extra work? (1 point)

Humans and Chimps share a 9,826 nucleotides out of 10,000 in sequences. Therefore, the Human and Chimp nucleotide difference out of 10,000 is 174. Gorillas and my new species differ by only 165 nucleotides. A) K=(-3/4)In(1-(4(0.0174)/3))=0.0176050171. L=K/2t=0.0176050171/2(6600000)=1.33x10^-9. B) K=(-3/4)In(1-(4(0.0165)/3))=0.0166842067. t=K/2L=0.0166842067. That is 6.2x10^6 years ago. By using the molecular clock method to estimate the two species, we can say that the species most likely diverged nearly 6 million years ago. C) I am uncertain what to write here but I assume future molecular clock calculations would be done... Comparing all other species known to the new species. Is any of this correct?

Answer 1

C)

By doingthe extra work, the evolutionary lineages between the these primate species and humans can be known and the divergence can be established by constucting the phylogenetic tree. The evolutionary relationship between the new species and other primates can be known and the relation between the new species with humans along with other primates can be clearly observed.

The molecular clock calculations are Ok.