Final answer:
Parts of a gene that are very similar among different species are termed highly conserved, which indicates their essential role in biological functions that are crucial across species. (Option 3 is the correct answer).
Step-by-step explanation:
Parts of a gene that are extremely similar among different species are termed highly conserved. These regions show sequence similarity across various organisms, highlighting their fundamental role in biological processes. Highly conserved genes tend to be crucial for basic cellular functions and developmental processes.
For example, genes essential for the embryonic development of animals are typically well conserved through evolution, indicating their importance across the animal kingdom.
The genetic conservation of these genes signifies that they have not undergone significant changes over long periods, which is evidence of their essential role and the evolutionary pressure to maintain their integrity.
This kind of stability is key for allowing the same or similar functions to be carried out in diverse species, exemplified by the retention of core processes such as transcription by polymerase, recognition of a consensus sequence in the promoter, and termination of transcription.