There are three types of substitution mutations that all produce different effects. The original DNA is on the left and the mutated nucleotide is on the right in red. Changing a cytosine to a thymine produces the same product: lysine. Missense Mutation A missense mutation is when a nucleotide gets changed, resulting in a different amino acid in the protein.
Nonsense Mutation A nonsense mutation is the worst type of substitution mutation. The original DNA strand is on the left. The first T is mutated into an A, which produces a stop codon. Related Lessons. View All Related Lessons. Gabi Slizewska. Samantha Broders. Substitution Mutations A substitution mutation occurs when specific bases A, T, C or G in a gene are swapped for different ones. Deena Hauze. What Are Substitution Mutations? A silent mutation is one where the function of the protein is not changed.
Here, find out the chromosomal aberrations involving the genes. Read More. Skip to content Main Navigation Search. Dictionary Articles Tutorials Biology Forum. Chromosome Mutations — II This tutorial is a continuation of the first lesson on chromosomal mutation. The amino acid change may alter the function of the protein. Nonsense : A nonsense variant is another type of substitution.
Instead of causing a change in one amino acid, however, the altered DNA sequence results in a stop signal that prematurely signals the cell to stop building a protein. This type of variant results in a shortened protein that may function improperly, be nonfunctional, or get broken down.
Insertion An insertion changes the DNA sequence by adding one or more nucleotides to the gene. Deletion A deletion changes the DNA sequence by removing at least one nucleotide in a gene. Deletion-Insertion This variant occurs when a deletion and insertion happen at the same time in the same location in the gene.
Duplication A duplication occurs when a stretch of one or more nucleotides in a gene is copied and repeated next to the original DNA sequence.
Inversion An inversion changes more than one nucleotide in a gene by replacing the original sequence with the same sequence in reverse order.
Frameshift A reading frame consists of groups of three nucleotides that each code for one amino acid. Repeat expansion Some regions of DNA contain short sequences of nucleotides that are repeated a number of times in a row. Topics in the Variants and Health chapter What is a gene variant and how do variants occur?
How can gene variants affect health and development? Do all gene variants affect health and development? Green, yellow, blue, and orange vertical rectangles that are twice as long and half as wide as the gray cylinders point upward from the gray cylinders, representing nitrogenous bases in each nucleotide. The left-hand end of the mRNA strand is labeled 3-prime, and the right-hand end is labeled 5-prime.
Each nucleotide is labeled with a letter representing the identity of the nitrogenous base. Three-nucleotide units, labeled below the letters as codons, are enclosed in brackets from left to right.
An arrow points from the codon to a colored sphere representing the corresponding amino acid coded for by the three-nucleotide-long mRNA sequence. Each amino acid is identified by its three-letter abbreviation.
Because there are 24 nucleotides, there are eight codons, each containing three nucleotides. The first codon, AUG, codes for the amino acid methionine, represented by a beige circle. The following codon, AAA, codes for the amino acid lysine, represented by a gray circle. The codon CUU codes for the amino acid leucine, represented by a brown circle. The last three codons all have the nucleotide sequence AUG, and therefore all code for the amino acid methionine, represented by a beige circle.
The final amino acid sequence coded for by the given mRNA sequence is methionine-lysine-leucine-arginine-arginine-methionine-methionine-methionine. Mutations can arise in cells of all types as a result of a variety of factors, including chance. In fact, some of the mutations discussed above are the result of spontaneous events during replication, and they are thus known as spontaneous mutations.
Slippage of the DNA template strand and subsequent insertion of an extra nucleotide is one example of a spontaneous mutation; excess flexibility of the DNA strand and the subsequent mispairing of bases is another. Environmental exposure to certain chemicals, ultraviolet radiation, or other external factors can also cause DNA to change.
These external agents of genetic change are called mutagens. Exposure to mutagens often causes alterations in the molecular structure of nucleotides, ultimately causing substitutions, insertions, and deletions in the DNA sequence. Mutations are a source of genetic diversity in populations, and, as mentioned previously, they can have widely varying individual effects. In some cases, mutations prove beneficial to an organism by making it better able to adapt to environmental factors.
In other situations, mutations are harmful to an organism — for instance, they might lead to increased susceptibility to illness or disease. In still other circumstances, mutations are neutral, proving neither beneficial nor detrimental outcomes to an organism. Thus, it is safe to say that the ultimate effects of mutations are as widely varied as the types of mutations themselves.
This page appears in the following eBook. Aa Aa Aa. Where do mutations occur? Germ-line mutations occur in gametes or in cells that eventually produce gametes. In contrast with somatic mutations, germ-line mutations are passed on to an organism's progeny.
As a result, future generations of organisms will carry the mutation in all of their cells both somatic and germ-line. What kinds of mutations exist? Base substitution. Base substitutions are the simplest type of gene-level mutation, and they involve the swapping of one nucleotide for another during DNA replication. For example, during replication, a thymine nucleotide might be inserted in place of a guanine nucleotide.
With base substitution mutations, only a single nucleotide within a gene sequence is changed, so only one codon is affected Figure 1. Figure 1: Only a single codon in the gene sequence is changed in base substitution mutation. The nitrogenous bases are paired so that blue and orange nucleotides are complementary and red and green nucleotides are complementary. However, the 5 th nucleotide from the right on both the bottom and top strand form a mismatched pair: an orange nucleotide pairs with a red nucleotide.
This mismatched pair is highlighted in cyan. The sugar molecules of each individual nucleotide in the chain are connected to adjacent sugar molecules, which are represented by gray horizontal cylinders.
The nitrogenous bases hang down from the sugar molecules and look like vertical bars that are twice as long and half as wide as the gray cylinders; the bases are either blue, red, green, or orange.
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