The Following Questions Refer to the Table Below, Which Compares $\quad$

question 69

Multiple Choice

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.
$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\text { \%/ Sequence Homology }$
$\begin{array} { l l l l l } \text { Species } & \text { Intron I } & \text { Exon I } & \text { Intron VI } & \text { Exon V } \\\text { A } & 100 \% & 100 \% & 100 \% & 100 \% \\\text { B } & 98 \% & 99 \% & 82 \% & 96 \% \\\text { C } & 98 \% & 99 \% & 89 \% & 96 \% \\\mathrm { D } & 99 \% & 99 \% & 92 \% & 97 \% \\\mathrm { E } & 98 \% & 99 \% & 80 \% & 94 \%\end{array}$
-Which of these is the best explanation for Intron I's relatively high sequence homology among these five species?

• A)It is the most-upstream of this gene's introns.
• B)It was once an exon, but became intronic in the common ancestor of these five species.
• C)Due to alternative gene splicing, it is often treated as an exon in these five species; as an exon, it codes for an important part of a polypeptide.
• D)It has a relatively high average rate of mutation.

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