The mutations that involve addition, deletion or substitution of a single base pair in a gene are referred to as

The correct option is A point mutations
Most of the gene. mutations involve a change in only a single nucleotide or nitrogen base of the cistron. These gene mutations are called point mutations e.g. sickle cell anemia in which polypeptide chain coding for haemoglobin contains valine instead of glutamic acid due to substitution ofT byA in second position of triplet codon.