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Comparing Gene Sequences Using BLAST


Scientists use the BLAST tool (Basic Local Alignment Search Tool) to search entire genomes for similar genetic sequences. Results from a BLAST provide an e-value; the lower the e-value, the closer the alignment between genetic sequences.

Any sequences with very small e-values (less than 1e$^{-04}$) are considered related with an error rate of less than 0.01%. After inputting a gene of interest, and running a nucleotide blast, a researcher finds that the chimpanzee actin gene sequence has an e-value of 0.00001 compared to the human actin gene.

Which of the following does this data indicate about the human actin gene sequence?


The very small e-value indicates that the species share the same genetic sequence, and mutations have not occurred in the actin gene among primates.


The small e-value indicates relatedness, showing that the actin gene in humans and chimpanzees can be considered highly conserved, since it is related with a very small error rate.


The e-value suggests a common distant ancestor. This supports the idea that humans and chimpanzees share a very distant common ancestor.


The e-value can only be used to determine relatedness between the same species, and not used for inter-species comparisons.