What are the effects of a point mutation?

A point mutation occurs in a genome when a single base pair is added, deleted or changed, altering the structure of the chromosome. The effects of a point mutation can vary based on whether it is a nonsense, missense, silent, or frameshift mutation.   

• Nonsense mutations, in which the substitution of a base pair forms a premature stop codon, are one of the more severe types of point mutation. They can lead to several serious medical conditions including severe anemia and beta thalassemias. 
• In missense mutations the substitution of a base pair creates a different amino acid in the resulting protein. Depending on the substitution and position, a missense mutation may not have any effect on the protein or it may lead to a nonfunctional protein. This type of mutation is associated with conditions such as sickle-cell anemia, ALS, and epidermolysis. 
• In silent mutations, the amino acid sequence formed after the alteration is almost the same as the original amino acid sequence. This causes no observable effects on the organism’s phenotypes because the amino acid sequence is the same before and after the alteration. 
• In a frameshift mutation, the nucleotides of a DNA sequence are altered such that one or more codons are changed resulting in an abnormally short or long polypeptide sequence that is mostly nonfunctional. This is a severe type of point mutation as it affects the amino acid sequence, which affects the protein formed. The effect of this type of point mutation depends on the position where the mutation occurs. If the mutation occurs earlier in the sequence, its effect is more prominent. Crohn’s disease is an example of a frameshift mutation.