How do determine the reference gene for SMN 2 - (Mar/29/2019 )

Where to determine the reference gene for SMN 2

It will depend a little bit on the species you are looking for but generally you can find this information on the National Center for Biotechnology Information (NCBI) website, which is part of the National Institutes of Health in the USA. They are generally considered to be the repository that stores the genome information for many many species. Most human mRNA references are indicated by an alphanumeric code that looks like "NM_#####.#", where # is a sequence of digits. For genomic sequences you will find the same format but with "NG_" at the start. Proteins are "NP_"

For instance, with a brief google search I found this for the human SMN2 gene, which led me to this page from the NCBI, where if you scroll down you will find a section entitled "NCBI Reference Sequences (RefSeq)" under which you will find the appropriate reference sequences for the genomic sequence, the various isoforms of mRNA and their associated proteins, as well as the information for the annotated genome assembly (note this may be different to the genomic reference, as assembly builds are whole genome), along with tons of other information.