The following questions refer to the table below, which compares the % sequence
ID: 14982 • Letter: T
Question
The following questions refer to the table below, which compares the % sequence homology of four different parts (2 introns and 2 exons) of a gene that is found in five different eukaryotic species. Each part is numbered to indicate its distance from the promoter (e.g., Intron I is that closest to the promoter). The data reported for Species A were obtained by comparing DNA from one member of species A to another member of Species A.% Sequence Homology
Species Intron I Exon I Intron VI Exon V
A 100% 100% 100% 100%
B 98% 99% 82% 96%
C 98% 99% 89% 96%
D 99% 99% 92% 97%
E 98% 99% 80% 94%
Which of these is the best explanation for the high degree of sequence homology observed in Exon I among these five species?
Due to alternative gene splicing, this exon is often treated as an intron.
A. These five species must actually constitute a single species.
B. It codes for a polypeptide domain that has a crucial function.
C. It is the most-upstream exon of this gene.
D. This exon is rich in G-C base pairs; thus, is more stable.
Explanation / Answer
B. It codes for a polypeptide domain that has a crucial function. Any time you have a highly conserved sequence across species, you are usually looking at a crucial domain. If the domain is altered in any way, the resulting protein product may not be functional. Thus, species requiring the function of that particular protein product will have very similar, if not identical, sequences since variation in the sequence will likely lead to a non-functional protein.
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