Science Assessment

Chikungunya is a disease that is transmitted to humans by infected mosquitoes. The disease, which causes fevers, rashes, and joint pain for years after infection, is caused by the Chikungunya virus.

In 2006, a new outbreak of Chikungunya infected many more people than usual. To understand why the disease was spreading, scientists collected samples of the virus from people infected in 2006 and found that three new strains of the virus had developed. They labeled these virus strains X, Y, and Z.  Then they compared the DNA sequences of these three new strains to the 2005 virus. They assumed that these new 2006 strains were all descended from the 2005 virus and were caused by a series of mutations in the DNA sequence of the 2005 virus. (The DNA sequence of each strain is represented by the letters ATGC.)

Key differences between the 2005 virus and the three new 2006 strains that the scientists found are highlighted below. For the following question, assume that each mutation happened only once and then was inherited by all descendants of the strain in which it occurred. You should also assume that once a mutation occurred in the DNA sequence, it did not mutate back to the original sequence.

1. TGAATAACATTGC
2. CGTCTGGCATTGC
3. CATTTAACACTGT
4. CGTTTAACATTGC