The difference between transcripts and isoforms

[crayfish]

Hi everyone, i got confused at the concept "transcripts" and "isoforms", in some paper they mentioned "transcripts", some paper mentioned "isoforms", some mentioned both, i thought they were the same, is that right? Sorry for this silly questions. Thank you very much!

[danwiththeplan]

An isoform is a specific splice variant of an expressed gene. I'd say that a transcript is too, but I think the word "transcript" tends to be used a lot more loosely than "isoform".

[Brian Bushnell]

An isoform is specifically one of many splice variants of a gene, while a transcript is an expressed sequence. The difference is that "isoform" implies that there are multiple isoforms, while transcript makes no such implication. For example, prokaryote genes are mostly not spliced, so referring to them as isoforms generally does not make sense. For eukaryote genes with conditionally-used exons, referring to the individual expressed sequences as isoforms is useful.

[crayfish]

"The difference is that "isoform" implies that there are multiple isoforms, while transcript makes no such implication"

Hi Brian, As you mentioned, i think isoform means there are alternative splicing, is that right? and for transcript can i suppose the expressed transcript is an expressed gene if this transcript has no isoform?

[danwiththeplan]

"The difference is that "isoform" implies that there are multiple isoforms, while transcript makes no such implication"

Hi Brian, As you mentioned, i think isoform means there are alternative splicing, is that right? and for transcript can i suppose the expressed transcript is an expressed gene if this transcript has no isoform?

It depends on your source and the paper you are reading, but I don't think you can assume that something referred to as a "transcript" has no alternative isoforms (unless it's a prokaryote). On the other hand, you can assume that something referred to as an isoform does have alternative isoforms.

That said, some bioinformatics pipelines (eg trinity) will automatically pick both "genes" and "isoforms" and in this case, the program can refer to something as an "isoform" even if it has only picked one "isoform".