 DNA replication is by no means perfect. Many errors can arise throughout this complex process, and in this video we'll have a look at some of these. Gene mutations occur when the sequence of nucleic acids are altered in some way, which may or may not change the regular functioning of the protein. Mutations develop over time, especially with sustained exposure to environmental factors, including chemical agents such as cigarette toxins, UV radiation such as sun exposure, and infectious agents such as the HPV virus. When investigating the types of mutations that can occur, DNA replication errors can be split into two main categories, which include point mutations and chromosome mutations. These categories can be separated further into sub-mutation types. Point mutations involve only single nucleotide changes within the sequence, and can be divided into substitution, insertion, or deletion mutations. Substitution mutations can either be silent, nonsense, or missense mutations. Insertion and deletion mutations result in a frame shift. Let's talk more about these in detail. Substitution mutations are where single nucleotides in the sequence are changed with a different nucleotide. This can result in three different types of alterations to the DNA sequence, such as silent, nonsense, or missense mutations. Silent mutations are where the amino acid being encoded has not changed as a result of the new nucleotide. Nonsense mutations result in a stop codon being expressed instead of the original amino acid. An example of this is with hemophilia, as nonsense mutations occur within genes of blood clotting proteins, which can result in the development of this condition. Missense mutations are when the nucleotide change results in a new amino acid being encoded. An example of this is sickle cell anemia, which can occur due to various mutations, one of which includes a missense mutation in the hemoglobin gene, resulting in an amino acid change. Mutations to both copies of this gene can cause the blood cells to change into a sickle or crescent shape. Let's have a look at an example. You may recall that each amino acid is coded for by a single codon, which is a triplet of three nucleotides. Therefore, the mutation altering any three of these nucleotides may alter the encoded amino acid. Prior to the point mutation, the triplet TTC encoded the amino acid lysine. If this triplet were changed to TTT, the encoded amino acid would still be lysine. Since there is no change in the encoded amino acid, this is a silent mutation. In the second example, the triplet is changed to ATC. This happens to code for a stop codon, meaning that the DNA sequence after this triplet will no longer be encoded. This usually has a significant effect on the DNA sequence. However, if the triplet were changed to TCC, the amino acid would be arginine. This new amino acid may have similar or very different functions to lysine, which may then alter protein function. The remaining two types of point mutations include insertions and deletions. Insertion involves the addition of a single nucleotide into the DNA sequence, while deletion involves the removal of a nucleotide. Unlike substitution mutations, both insertions and deletion mutations produce a frame shift, which is where a triplet grouping of the DNA are altered. Once a triplet is altered within a sequence, the remainder of the sequence will also be affected. Let's take a look at an example for insertion. Prior to the nucleotide insertion, the DNA sequence produced the following amino acid sequence shown. After the addition of a C nucleotide to the third triplet indicated by the blue, you can see that the triplet groupings change for the rest of the sequence. Similarly, you can see that after the nucleotide insertion, the amino acids being encoded have also changed. If we look at this example for deletion, the T nucleotide in the fifth triplet in red is removed as shown by the bottom DNA sequence. This alters both the DNA and encoded amino acid sequence after the deletion point. Along with point mutations, you can also have chromosome mutations. Chromosome mutations differ from point mutations as they result in changes to large segments of DNA rather than just single nucleotides. This can result in drastic changes. As shown by the flowchart, chromosome mutations can be split into duplications, deletions, inversions, and translocations. Duplication mutations are where a segment of genetic material are spliced from a chromosome and are inserted into the homologous chromosome. Homologous chromosomes refer to the other chromosome in the pair, as chromosomes occur in pairs of two. Deletion mutations are where DNAs split at two points in the sequence, and this sequence of genetic material is lost. This deletion shortens the chromosome, which can have detrimental effects. Inversion mutations are where a segment of DNA is split at two points. This sequence is then rotated 180 degrees and then reinserted back into its original location on the same chromosome. Translocation mutations are where segments of DNA are removed from one chromosome and is inserted at a location on a non-homologous chromosome. These chromosome mutations can occur due to errors during meiosis, being that they arise on the chromosome. Meiosis involves significant genetic exchange to produce variability. The process of crossing over can be easily completed incorrectly. Chromosome mutations can be caused by unequal crossing over, where the chromosomes do not exchange equal amounts of DNA, non-destunction of chromosomes, where chromosomes do not correctly separate, as well as incorrect duplication of RNA. In summary, in this video we covered two different types of mutations that can arise, which were point mutations and chromosome mutations. The three types of point mutations that can occur include substitution, insertion, and deletion. Chromosome mutations, on the other hand, happen in four different ways, which include duplication, deletion, inversion, and translocation. By understanding the different types of mutations that can arise throughout the complex processes of DNA replication, we can also understand their potential effects on protein function.