▶️ Answer/Explanation
The degree of similarity in DNA base sequences is determined by how recently species shared a common ancestor. According to the data, $P$ and $Q$ are closely related, and $S$ is very closely related to $P$ because it branched off recently. This places $P, Q,$ and $S$ in a relatively tight evolutionary cluster. In contrast, species $R$ shared a common ancestor with the others much further back in time. Because more time has passed since $R$ diverged, more mutations have accumulated, resulting in the greatest number of differences in its DNA sequence compared to the other three. Therefore, $R$ is the most genetically distinct.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Binomial nomenclature uses two names: the first is the genus and the second is the species. Both rats share the first name, Rattus, meaning they belong to the same genus. They have different second names (norvegicus vs. rattus), which indicates they are different species. Because they are different species, they generally cannot breed to produce fertile offspring, making option (B) and (C) incorrect. Since they are in the same genus, they naturally share many biological features, making (D) incorrect.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
The system used to name organisms is called binomial nomenclature, developed by Carl Linnaeus. This system uses two Latin words to uniquely identify every species. The first part of the name represents the genus, which is always capitalized, and the second part represents the species (or specific epithet), which is written in lowercase. Together, these two levels of classification provide a precise “first and last name” for an organism, ensuring scientists worldwide use the same terminology regardless of local common names. For example, in Homo sapiens, Homo is the genus and sapiens is the species.
✅ Answer: (B)
✅ Answer: (B)