Effect of genetic variants on phenotype - Higher
Coding and non-coding DNA
The structure of DNA is important in synthesising specific proteins needed in biological processes.
Not all parts of the DNA code for proteins. There are coding and non-coding part of DNA, which can switch genes on and off.
The diagram below shows DNA with certain genes switched on and some switched off:
The next diagram shows all of the genes are switched off:
In different cells around the body, some genes will be switched on and others will be switched off. This will vary depending on which cells you examine.
Only about 1.5 per cent of human DNA is Regions (genes) in the genome of an organism that store the genetic code for making proteins. and 98.5 per cent is Regions in the genome that do not store code for making proteins, but that affect gene expression.. Mutations that occur in non-coding DNA may affect the expression of genes in coding DNA sections. Variations in these areas may affect When genes are instructed to make gene products, mostly proteins. Controlling gene expression means controlling which proteins are made by the cell., and control whether the correct protein is synthesised or not.
An example has been found in DNA that controls limb development in vertebrates. The DNA sequence responsible for limb development in chimpanzees and humans is similar, but not identical. In a single length of 81 base pairs, over the course of evolution there have been 13 separate point mutations between the two species, causing 13 different nucleotides to occur in human DNA compared to chimpanzee DNA. This non-coding DNA sequence is called HACNS1.
The mutations have resulted in an increase in the expression of a coding gene which is active during the formation of the hand, causing shorter fingers and an opposable thumb. This means that the human hand is better at picking things up and throwing than that of chimpanzees.