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

question 49

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 }$
$\begin{array} { l l l l l } \text { Species } & \text { Intron I } & \text { Exon I } & \text { Intron VI } & \text { Exon V } \\\text { A } & 100 \% & 100 \% & 100 \% & 100 \% \\\text { B } & 98 \% & 99 \% & 82 \% & 96 \% \\\text { C } & 98 \% & 99 \% & 89 \% & 96 \% \\\mathrm { D } & 99 \% & 99 \% & 92 \% & 97 \% \\\mathrm { E } & 98 \% & 99 \% & 80 \% & 94 \%\end{array}$
-The human nuclear genome includes hundreds of genes that are orthologs of bacterial genes, and hundreds of other genes that are orthologs of archaean genes. This finding can be explained by proposing that

• A)neither archaea nor bacteria contain paralogous genes.
• B)the eukaryotic lineage leading to humans involved at least one fusion of an ancient bacterium with an ancient archaean.
• C)the infection of humans by bacteriophage introduced prokaryotic genes into the human genome.
• D)horizontal gene transfer did not occur to any significant extent among the prokaryotic ancestors of humans.

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