How do mutations affect the phenotype?
Some mutations don't have any noticeable effect on the phenotype of an organism. This can happen in many situations: perhaps the mutation occurs in a stretch of DNA with no function, or perhaps the mutation occurs in a protein-coding region, but ends up not affecting the amino acid sequence of the protein.
Sometimes a silent mutation results in the same exact sequence of amino acids. That's what happened here. Other times in a silent mutation, there is an amino acid change, but it doesn't affect the overall function of the protein.
- Mutations are changes in a DNA sequence, and they can occur due to radiation or other types of DNA damage. But not always; a silent mutation is a type of mutation in the coding region of a gene that doesn't actually change the amino acid sequence of the protein that is made.
- “Silent” mutation: does not change an amino acid, but in some cases can still have a phenotypic effect, e.g., by speeding up or slowing down protein synthesis, or by affecting splicing. Frameshift mutation: Deletion or insertion of a number of bases that is not a multiple of 3.
- Briefly, the DNA in our cells is translated by cell machinery to make proteins. The sequence of amino acids in a protein determines its function. The DNA sequence of a gene determines the amino acid sequence of the resulting protein. Thus, any changes in DNA sequence can result in changes in protein function.
The Sound of a Silent Mutation. Silent mutations occur when the change of a single DNA nucleotide within a protein-coding portion of a gene does not affect the sequence of amino acids that make up the gene's protein.
- There are three types of point mutation: Silent Mutation: There is a base change, but the new codon means exactly the same thing as the old one; this is due to the degeneracy of the codon -> amino acid conversion code. There is no phenotypic change.
- By the same token, any random change in a gene's DNA is likely to result in a protein that does not function normally or may not function at all. Such mutations are likely to be harmful. Harmful mutations may cause genetic disorders or cancer. A genetic disorder is a disease caused by a mutation in one or a few genes.
- In genetics, a nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA, and in a truncated, incomplete, and usually nonfunctional protein product. Some genetic disorders, such as thalassemia and DMD, result from nonsense mutations.
We have seen that the information in DNA is the starting point of gene expression. The cell transcribes that information into mRNA and then translates the mRNA information into protein. Mutations that alter the nucleotide pairs of DNA may modify any of the steps or products of gene expression.
- Cancer is caused by changes (mutations) to the DNA within cells. The DNA inside a cell is packaged into a large number of individual genes, each of which contains a set of instructions telling the cell what functions to perform, as well as how to grow and divide.
- But the mutations we hear about most often are the ones that cause disease. Some well-known inherited genetic disorders include cystic fibrosis, sickle cell anemia, Tay-Sachs disease, phenylketonuria and color-blindness, among many others. All of these disorders are caused by the mutation of a single gene.
- The protein may lose its function, which can result in a disease in the organism. For example, sickle-cell disease is caused by a single point mutation (a missense mutation) in the beta-hemoglobin gene that converts a GAG codon into GUG, which encodes the amino acid valine rather than glutamic acid.
Updated: 26th October 2019