A gene mutation is
a permanent alteration in the DNA sequence that makes up a gene, such that the
sequence differs from what is found in most people. Mutations range in size;
they can affect anywhere from a single DNA building block (base pair) to a large segment
of a chromosome
that includes multiple genes. Gene mutations are of two types Hereditary
mutations and Acquired (or somatic) mutations. The former
inherited from a parent and are present throughout a person’s life in virtually
every cell in the body and the latter occur at some time during a person’s life
and are present only in certain cells, not in every cell in the body. Genetic alterations
that occur in more than 1 percent of the population are called polymorphisms.
They are common enough to be considered a normal variation in the DNA.
Polymorphisms are responsible for many of the normal differences between people
such as eye color, hair color, and blood type.