Final answer:
Among the 239 protein-coding gene families found across Bacteria, Archaea, and Eukaryota, genes involved in photosynthesis would not be expected to be included because not all organisms in these domains perform photosynthesis.
Step-by-step explanation:
In comparing the complete genomes of organisms from the different domains - Bacteria, Archaea, and Eukaryota - 239 families of protein-coding genes have been found to have representatives across these domains. However, in this selection of genes, one would not expect to find genes involved in photosynthesis to be among those present in all three domains, as photosynthesis is not a fundamental process to all domains of life. Specifically, many archaea do not carry out photosynthesis, and genes related to this process are also not found in all eukaryotes, with a notable example being yeast, where photosynthesis does not occur. On the other hand, genes involved in fundamental cellular processes such as transcription, translation, and DNA replication are likely to be conserved across all domains because they are essential for the basic functions of life.