Q:

Names of different cyclins

Different types of cell cyclins are designated as a to y
Why are some letters like m, n, p, q.. etc. skipped?

Source: https://en.wikipedia.org/wiki/Cyclin

A:

Biological nomenclature can be impenetrable. Almost certainly, at some point in history, there were cyclins designated with these letters. Researchers would have discovered apparently novel cyclins which were subsequently determined to be part of an existing family and renamed. For example, this paper reports the discovery of:

a new cyclin, cyclin M, which appears to be most closely related to cyclin L. Its biological function is unknown, but it is related to cyclins that regulate transcription.

It is now called cyclin L2.
I hope this answer satisfies you to some extent. I doubt anyone is going to sift through the literature and try and determine why all cyclins are are named as they are; that is certainly a losing proposition. The naming of genes/proteins is rather trivial and doesn't generally follow any specific set of rules. Outside of curiosity, the knowledge of cyclin naming doesn't have much, if any, practical relevance.

