“Scientists have recently proposed a reorganization of the phylogenetic system of classification to include the domain, a taxonomic category higher than the kingdom category.”
A. The three-domain system allows for the conclusion that the previous five kingdoms were more connected than was believed. Out of the five previous kingdoms: Animalia, Plantae, Protista, Fungi, and Monera, four of the five kingdoms were placed in the same domain- Eukarya. The one remaining kingdom was separated into two domains- Bacteria and Archaea. This separation was unusual as it was previously thought that Bacteria and Archaea were closely related, as they were both prokaryotic.
It is now thought that Archaea is more closely related to Eukarya than it is to Bacteria. B. Recommendations to adopt this new three-domain taxonomic system were based on evidence more detailed and reliable than that of the five-kingdom system. New advances in genetic and molecular sciences have allowed for classification based on information such as base composition, nucleic acid hybridization, and amino acid sequences.
The two main molecular methods to identify microbes are by the comparison of 1) DNA and RNA sequences (nucleic acid hybridization) and 2) of amino acid sequences of a protein or proteins (amino acid sequences). Nucleic acid hybridization, a part of the field molecular genetics, is used to identify related DNA and RNA molecules. It takes into account single stranded genetic material’s ability to multiply into double-stranded genetic material, and how the double-stranded material (DNA) still has some resemblance to the one-stranded genetic material. DNA base composition is a genetic method used to compare related organisms through their genetic material (DNA).
This new more scientifically sound evidence has enabled new findings such as Achaea’s newfound relation to Eukaryotes. Physically, Archaea seemed to be more closely related to bacteria, but genetically Archaea has been found to have DNA that is structurally more similar to ours. It is believed that Eukaryotes were once a part of Archaea, but split off due to evolution at some point in history. C. The universal ancestor is the base organism from which all other organisms have evolved. The universal ancestor was most likely small, unicellular, prokaryotic, and contained a cell membrane. Its small size would have given it a low surface area to volume ratio and no internal transport system. The universal ancestor would have been completely self-contained and would have used its semipermeable cell wall for protection.