Just as in mitosis, cohesin is an important protein that keeps chromatids together during meiosis and is similarly targeted by separate as well. in the context of meiosis, however, there are multiple variants of cohesin with different quaternary structures. why do you think this is necessary?

It is well known that in biological compounds, such as proteins; a small change on its structure modifies its function to send a different signal or even to not have a function at all.

Talking about cohesin, this protein has been implicated in the development of certain types of tumors, because it takes a fundamental role in the cellular division and the 3D structure of the genome. Cohesin SA1, for example, maintains differentiated the TADs and it is essential for the organization of the topological domains of the genome, while the Cohesin SA2 is much more versatile and can regulate the expression of the genes within TADs, it is also capable to bond to some transcription factors creating local loops.

Some mutations on this protein can also be involved in the origin of rare diseases.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.