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Mutations by Rashi Rathore
- 1. MUTATIONS
- 2. DNA:The Molecular Basis of Mutations DNA is made of a long sequence of smaller units strung together. There are four basic types of unit: A, T, G, and C. These letters represents the type of base each unit carries: adenine, thymine, guanine, and cytosine. The sequence of these bases encodes instructions. Some parts of your DNA are control centers for turning genes on and off, some parts have no function, and some parts have a function that we don't understand yet. Other parts of your DNA are genes that carry the instructions for making proteins — which are long chains of amino acids. These proteins help build an organism. Protein-coding DNA can be divided into codons — sets of three bases that specify an amino acid or signal the end of the protein. Codons are identified by the bases that make them up — in the example at right, GCA, for guanine, cytosine, and adenine. The cellular machinery uses these instructions to assemble a string of corresponding amino acids (one amino acid for each three bases) that form a protein. The amino acid that corresponds to "GCA" is called alanine; there are twenty different amino acids synthesized this way in humans. "Stop" codons signify the end of the newly built protein. After the protein is built based on the sequence of bases in the gene, the completed protein is released to do its job in the cell.
- 3. DEFINITION A mutation occurs when a DNA gene is damaged or changed in such a way as to alter the genetic message carried by that gene. A Mutagen is an agent of substance that can bring about a permanent alteration to the physical composition of a DNA gene such that the genetic message is changed.
- 4. • Over a lifetime, our DNA can undergo changes or ‘mutations’ in the sequence of bases, A, T, G and C This results to changes in the proteins that are made. This can be a bad or a good thing • Mutations can occur during DNA replication, if errors are made and not corrected in time • Mutations can also occur as the result of exposure to environmental factors such as smoking, sunlight and radiation • Often cells can recognize any potentially mutation-causing damage and repair it before it becomes a fixed mutation • Mutations contribute to genetic variation within species • Mutations can also be inherited, particularly if they have a positive effect For example, the disorder sickle cell anaemia is caused by a mutation in the gene that instructs the building of a protein called haemoglobin. This causes the red blood cells to become an abnormal, rigid, sickle shaped. However, in African populations, having this mutation also protects against malaria.
- 5. TYPES OF MUTATIONS Gene Mutation Point Mutation Frameshift Mutation Chromosomal Mutation Deletion Duplication Inversion Translocation Nondisjunction
- 6. GENE MUTATION A gene mutation is a permanent alteration in the DNA sequence that makes up a gene, such that the sequence differs from what is found in most people. Mutations range in size; they can affect anywhere from a single DNA building block (base pair) to a large segment of a chromosome that includes multiple genes
- 7. • POINT MUTATION A point mutation or substitution is a genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of an organism's genome. 3 Possible Consequences: Nonsense mutations: code for a stop, which can translate the protein. Ex. Cystic Fibrosis. Missense mutations: code for a different amino acid. Ex. Sickle cell anaemia. Silent mutations: code for the same amino acid. Ex. Mutation producing leucine instead of isoleucine. • FRAME-SHIFT MUTATION A frameshift mutation (also called a framing error or a reading frame shift) is a genetic mutation caused by indels (insertions or deletions) of a number of nucleotides in a DNA sequence that is not divisible by three. Example – Cystic Fibrosis.
- 8. CHROMOSOMAL MUTATIONS Chromosome mutation is the process of change that results in rearranged chromosome parts, abnormal numbers of individual chromosomes, or abnormal numbers of chromosome sets.
- 9. • DELETION Deletion is a type of mutation involving the loss of genetic material. It can be small, involving a single missing DNA base pair, or large, involving a piece of a chromosome • DUPLICATION Duplication is a type of mutation that involves the production of one or more copies of a gene or region of a chromosome
- 10. • INVERSION An inversion occurs when a chromosome breaks in two places and the region between the break rotates 180° before rejoining with the two end fragments. • TRANSLOCATION Translocation is a type of chromosomal abnormality in which a chromosome breaks and a portion of it reattaches to a different chromosome. Chromosomal translocations can be detected by analyzing karyotypes of the affected cells. • NONDISJUNCTION Failure of paired chromosomes to separate (to disjoin) during cell division, so that both chromosomes go to one daughter cell and none go to the other.
- 11. DNA MUTATIONS: Base Substitution • Transitions • Transversions
- 12. Single base substitutions are called point mutations, recall the point mutation Glu -----> Val which causes sickle-cell disease. Point mutations are the most common type of mutation and there are two types. Transition: this occurs when a purine is substituted with another purine or when a pyrimidine is substituted with another pyrimidine. Transversion: when a purine is substituted for a pyrimidine or a pyrimidine replaces a purine.
- 13. DNATAUTOMERS An error in DNA replication can occur when an illegitimate nucleotide pair (say, A–C) forms in DNA synthesis, leading to a base substitution. Each of the bases in DNA can appear in one of several forms, called Tautomers, which are isomers that differ in the positions of their atoms and in the bonds between the atoms.