Understanding Chromosomes: How Parental Genes are Activated in Somatic Cells

[Dr. Nick]

Two same chromosomes, each from one parent in our somatic cells.

So how is it chosen which one will be active in one cell ? Here I wonder, are 2 chromosomes, mother’s and father’s, active and “uncoiled” at the same time in the cell, or only one is uncoiled and used as template ?

 

[quasi426]

From what I've learned it is usually both. You are getting a mixture of both chromosomes, or both kinds of proteins. This means that if the DNA sequence is not exactly the same and leads to a different amino acid sequence then you will have a mixture of the same protein. This is why some genes are recessive and dominant. Usually the dominant gene only requires one chromsome from one parent.

Reasons why only part of one would be active are:
One parent gave you a chromosome that has a portion that is not expressed due to mutations that inhibit transcription such as the inability to perform 'uncoiling.'

 

[Dr. Nick]

Thank you, I’ve asked this because I thought I’ve read in some cytology book that only one chromosome is active in some cells at the time…

 

[gamze]

Thank you, I’ve asked this because I thought I’ve read in some cytology book that only one chromosome is active in some cells at the time…

That's true for X chromosomes of females in mammals. To compensate for the presence of an additional X chromosome, females shut off expression of one of the X chromosomes.