Question

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.
What does this data indicate about the human actin gene sequence?

• A. 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.
• B. 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.
• C. The e-value suggests a common distant ancestor. This supports the idea that humans and chimpanzees share a very distant common ancestor.
• D. The e-value can only be used to determine relatedness between the same species, and not used for inter-species comparisons.

Answer 1

The correct option is A 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.

BLAST is a powerful tool that finds similarities between the reference and experimental sequences of DNA. The algorithm can find differences in the sequences of proteins, DNA, RNA and nucleotides.

The E value or the expected value is the number of significant matches one can expect to see when they math 2 sequences together.

The lower the E value the more significant the match is that is lesser mutations took place in the gene or the sequence over the course of time.

So, the correct option is '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.'