I have completely dummy question.

I have 23 pairs of chromosomes in the cells 23 single coming from my mother and 23 single from my father. So how my cell choose which chromosome, mother's or father's to use to synthesize peptides?

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    $\begingroup$ Actually, both sets of chromosomes are used to synthesize proteins. This is true for most proteins, ignoring things like imprinting and X-inactivation, which is a bit more advanced to grasp. $\endgroup$
    – Arcadium
    Nov 5, 2015 at 21:53
  • 2
    $\begingroup$ I dont find it a dummy question. Article "gene expression" on wikipedia does not provide a solution to this question. $\endgroup$
    – TMOTTM
    Nov 23, 2015 at 20:52

1 Answer 1


The majority of normal autosomal genes have biallelic expression, i.e. the alleles on both chromosomes are used to make protein. This is why mutations in a gene which cause non-function of the product can be silent if the mutation is heterozygous (only found on one of the alleles), because the effect is masked by the second, fully-functional, copy of the gene. In other cases heterozygous mutations may cause slight phenotypes, because half of the protein produced is non-functional.

A small minority of autosomal genes have monoallelic expression, through a process called imprinting. This is where one of the alleles of the gene is modified by methylation of the DNA, or of histones (the proteins which are used to package and condense DNA). This imprinting switches off the expression of that allele, so that protein is only made from the other allele of the gene. Usually in this case, which allele is switched off depends on which parent it came from.

Things are slightly more complicated in the case of genes on X or Y chromosomes. Men have only a single X chromosome, and a single Y chromosome. This means that any mutation on X or Y which causes a phenotype will always present itself, because there is no second copy to mask it.

In the case of women, who have two X chromosomes and no Y, something similar to imprinting happens, where one of the X chromosomes is chosen to be inactivated. This X-inactivation process occurs very early in development, and the inactive X chromosome is kept that way for the rest of that person's life. In this case, however, the choice of which chromosome is inactivated is not dependent on which parent the chromosome came from, and is entirely random.

Some further reading:



  • 2
    $\begingroup$ According to some moderators you need to go into the intricacies of monoallelic expression in detail or else this is an incomplete answer. $\endgroup$
    – Arcadium
    Nov 6, 2015 at 13:29
  • $\begingroup$ @OmarMourad how is it now? thanks for the feedback, this is the first question I've answered on SE $\endgroup$
    – mtp
    Nov 6, 2015 at 15:02
  • $\begingroup$ I considered this to be an extremely clear and thorough answer. $\endgroup$
    – wil3
    Oct 6, 2017 at 7:47

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