Gene copy number is the number of copies of a particular gene present in a cell while Gene isoforms are transcriptional variants that are produced from the same gene.

You mean isoforms are transcriptional variants therefore produced by alternative splicing from a single gene. there are several papers e.g. related to calcium transporters,Calmodulin gene, the papers say for example there are 7 Calmodulin (CaM) genes in Arabidopsis CaM1 to CaM7 each encoding similar or identical "isoforms"

Paper-"Breaking the code:Ca sensors in plant signalling" www.ncbi.nlm.nih.gov/pubmed/20001960

This means that product of different but related genes are also considered as isoforms.

I think the term isoform (or especially isoenzyme/isozyme) is used for proteins coded by homologous, but distinct genes

Vinay, I know what isozymes are and I also had d same knowledge as u hv written. kindly go thru d first para of d 2nd page of d paper i have mentioned, may b then u'll b able to understand why am I askin dis question

Thank u very much. and let me tell u where u have written,

2. These multiple genes (100 % similar genes)...

Firstly, these r not 100% identical genes, they r paralogs, dats why different names CaM1, CaM2....

Secondly, Isoforms are variant proteins that r mostly derived from splice variants (i.e. transcripts) from a single gene but may also come from closely related (paralogs) genes within a given organism.

Well, I read d paper again and some others n got my answer.

Thanks anyways!