Mutations are hereditary and permanent changes in DNA structure. Mutations can occur spontaneously during DNA replication or they can be induced by mutagenic agents. Point mutations are a type of mutation that causes the replacement of a single base nucleotide with another nucleotide in DNA and they are responsible for many diseases. Sickle cell anemia was the first disease known to be caused by one point mutation. The cause of this disease is one point mutation in ß globin chain of hemoglobin which leads to formation of abnormal erythrocytes and that often includes severe and lethal consequences for the patient. Occurance of this mutation in tropic and subtropic areas, where malaria is also very common, made persons who were heterozygous for sickle cell anemia better adapted because this way they had much greater chance of surviving malaria. Point mutations that occur in mitochondrial DNA (mtDNA) are inherited only by mother line and since mitochondrion does not have intrones similar to those in nuclear genome of eucaryotes, these mutations usually affect coding region of mtDNA. Examples of such diseases are MELAS syndrome and Leber's hereditary optic neuropathy. MELAS syndrome is a severe and lethal disease caused by defect in proteins that build complex I in mitochondrion. It specially affects brain and muscle tissue which mostly depend on cell's ATP produced during the process of oxidative phosphorylation in mitochondrion. Leber's hereditary optic neuropathy causes complete loss of vision and it affects very young persons. Today researchers aim to find new methods for point mutations detection. They are also trying to discover various other methods of point mutations threatment like gene therapy. These methods help reduce negative effects of mutations on cells and organisms.