Gene duplication can give rise to homologous genes that are part of gene families. For example, there are six actin genes in the genome of most mammalian species. In humans, the ACTB gene, which encodes a cytoskeletal actin, is expressed ubiquitously, while ACTC1 is expressed mainly in cardiac cells. Although bacteria lack the eukaryotic cytoskeletal organization, the bacterial MreB gene bears recognizable sequence similarity to mammalian actin genes and codes for a protein that is similar to actin in structure and function. Which of the following statements is true about these genes?
A) ACTB is homologous to ACTC1 but not to MreB.
B) ACTB is orthologous to ACTC1 but not to MreB.
C) ACTB is paralogous to ACTC1 but not to MreB.
D) MreB is orthologous to ACTB but not to ACTC1.
E) ACTB is paralogous to both ACTC1 and MreB.