After gene duplication, duplicates can have different functional fates, such as maintaining the same function as the ancestral single-copy gene, developing a new function, etc.
In fact, novel copies, being initially free from selective pressure because of their functional redundancy, depending on the relative forces of selection and drift may: i) remain very similar to the original copy and maintain the same function; ii) diverge and acquire a new function (neo-functionalization); or iii) lose their function and become pseudogenes (pseudogenization).
If the muscles are fatigued or are in a condition of spasm, they must recruit more motor units to maintain the same function.
On the other hand, duplicated genes can also maintain the same function in the course of evolution, thereby enabling the production of a large quantity of RNAs or proteins (gene dosage effect).
Since orthologs often maintain the same function during evolution, we conjecture that the expression of these genes might also be responsive to PM fungi attacking corresponding species.
Orthologous genes are defined as homologous genes, which originated from a common ancestor, and subsequently diverged from the original sequence, usually maintaining the same function.
However, whether these identified homologs in Euryarchaeota maintain the same function as their bacterial homologs and whether these functions are substituted by other translocases in other archaea remain interesting issues for further studies.
Conservation of two paralogous genes maintaining the same function is unlikely, and could only be explained under some peculiar conditions (e.g. two strongly expressed genes whose products are in high demand [ 40]).
The low dN/dS between C. virginica and C. gigas indicates purifying selection in the coding regions of orthologous genes and provides justification that genes identified as osmoregulatory in C. gigas are likely to maintain the same function in C. virginica.
(iv) The ranking of probabilities of within-operon PIs and of across-operon PIs is identical in every species, since Che proteins maintain the same functions across species.
