Question

You are studying the source of new virus that has recently infected humans. You suspect that the virus was transferred from other primates (they exhibit a similar infection), specifically chimpanzees, gorillas, or orangutans. You sample blood from several infected humans and sequence some viral genes. You then build a phylogenetic tree with the human sequences and all the known strains from each primate. Draw a hypothetical phylogenetic tree that would suggest that the virus came from gorillas, and this transfer occurred twice independently. Label chimp sequences (c), gorilla (g), orangutans (o), and humans (h).

Answer 1

Since the virus has been inherited in the animals from non-human primates, there should be a single immediate primate from where the virus must have been transferred from. Also, the fact that all the primates have a similar inheritance from a single ancestor suggests a linear phylogeny of the virus. Thus, the phylogenetic tree suggesting a transfer from two independent events, say from an ancestor to gorillas and then to humans can be found as below: