During transcription, mRNA is copied from a chromosome. But since the chromosomes are in homologous pairs, which chromosome in the pair is the mRNA made from?

Question

And does it matter from which chromosome in the pair the mRNA is copied from? I think it does because the two chromosomes have different alleles. 

Answer 1

Marco,

 

mRNA is not transcribed from chromosomes, it is transcribe from DNA.

 

Chromosomes are made of nucleosomes that include DNA and different kinds of histone proteins. In cell, supercoiled chromatin (made of all chromosomes in the cell) first unwinds and chromosomes appear, then depending on cell type chromosomes split in chromatids that replicate during cell division.

 

At the specific time point during development or any other life-point when a gene function is required, the DNA of the gene in question would unwind on chromosome, nucleosomes would change their configuration during this unwinding and DNA strands would separate. The coding strand would make mRNA, in other words mRNA would transcribe from the coding strand. 

 

In mammalian females, one X chromosome is always inactive and transcription always occurs from genes/DNA of  active chromosome.

 

For autosomes, cells have intrinsic regulatory mechanisms that control active chromosomes from where DNA unwinds and coding strand is transcribed.

 

Hope this helps.