Point mutation is a type of genetic mutation in which a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of a genome of an organism. It usually takes place during DNA replication. Ethylmethane sulfonate and N-methyl-N-nitrosourea are the most common chemical mutagens that induce point mutations in DNA.
It is also known to cause disease in humans. The most common diseases caused due to point mutations in humans are sickle cell anemia, cancer and Neurofibromatosis. Due to point mutation in the β-globin chain of hemoglobin, hydrophilic amino acid and glutamic acid get replaced with the hydrophobic amino acid valine at the sixth position which causes sickle cell anemia.
But, it is helpful to make precisely targeted changes in the DNA encoding to eliminate the chances of diseases or pests in plants as well as animals. With the help of point mutation in plant breeding, we can rapidly create new varieties that are resistant to diseases, have high nutrient content, have better adaptability and have a longer shelf life.
There are three types of point mutations, namely: Nonsense mutations, Missense mutations and Silent mutations. In nonsense mutations, a codon for an amino acid is changed to a stop codon which results in a disfunctional protein. In missense mutations, a codon gets changed so that a different protein is created, sometimes altering the function of the created protein. Sickle cell anemia is an example of a missense mutation.
Missense mutation can be conservative and non-conservative mutation. In conservative mutations, amino acid changes but the properties remain the same. But, in non-conservative mutation amino acid change results in different properties than the native type.
In silent mutation, a single nucleotide can change, but the new codon specifies the same amino acid and has no effect on the functioning of the protein.