Mutations By: Ayan Mohamud

What is a mutation? Mutations are errors made in the DNA sequence that are inherited. The errors may have severe side effects, positive side effects or none. Organisms have evolved because of mutations that have been naturally selected. For example the large size of the human brain is a result of a mutation that lead to a positive side effect. Because humans are diploid organisms we have two copies of each gene so it an error is made in one copy the other copy can compensate for that specifc error. This positive mutation is what allows humans to survive because if we were haploid, the majority of the worlds population would not survive because of the many life threatening mutations we carry.

Types of mutations : Mutations can occur in two different types of cells Gamete (sex cells) Somatic (body cells) Mutations that occur in gamete (sex) cells means that every cell of the developing fetus will have that mutation. Gamete mutations affect the individual with some type of disorder and the mutation can be passed on to the next generation. Two types of gamete mutations that occur : Gene mutation and Chromosomal mutation Mutations that occur in the somataic cell usually resut in the death of that cell only. An exception to this is if the mutation occurs to the DNA that controls regulation of the cell cycle. This can result in cancer. Somatic mutations usually do not affect the individual. Somatic mutations cannot be passed on to the next generation.

Types of single gene mutations:Point Mutation Mutations at a specific base pair in the genome. Silent, insertion and deletion mutations all occur at a certain point in the base sequence and only involve one base pair. All three of these mutations fall under the category of point mutation. Point mutation can be a substitution in which one base is replaced by another. Original Sequence DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA Amino Acid: Met - Arg - Thr - Leu (In this DNA sequence the 5th base in the DNA sequence has been changed) Mutated Sequence DNA: TAC GTA TGG AAT mRNA: AUG CAU ACC UUA Amino Acid: Met - His - Thr - Leu

Types of mutations: Frameshift mutation Frameshift mutation is a mutation that causes the reading frame of codons to change which results in a different amino acid being built into the polypeptide. This type of mutation can be an insertion in which one base is inserted in the DNA sequence. It can also be a deletion in which one base is deleted in the sequence. A deletion or insertion of a codon does not result in a shift in the reading frame, furthermore it results in the addition or removal of one amino acid. The affect of frameshift mutation is more dramtic than point mutation because it can alter a protein so much so that the protein can no longer perform its normal function.

Chromosomal mutations There are five types of chromosomal mutations: 1.Deletion 2.Duplication 3.Inversion 4.Translocation 5.Non-disjunction Deletion: The elimination of a base pair of base pairs from a DNA sequence. Duplication: Involves the production of extra copies of parts of the chromosome. Inversion: Reverses the direction of parts of a chromosome. Translocation: When one part of a chromosome breaks off and attaches to another chromosome. Non-disjunction: Means not coming apart. When homologous chromosomes fail to separate properly during meiosis. Results in abnormal numbers of chromosomes. Typically you have 2 of each. Trisomy means a person has an extra copy of a chromosome. Monosomy means a person is missing a copy of a chromosome.

Chromosomal mutation cont. NON-DISJUNCTION

Base substitution Base mutations can have several types of effects within an organism, and this type of mutation is in the category of silent mutations. A missense mutation refers to a base substituiton when the change in the nucleotide changes the amino acid that was coded for. A nonsense mutation refers to a base substitution in which the changed codon changes the codon into a stop codon. This change causes an ealry termination of translation which affects the production of proteins.

Missense and Nonsense Mutations cont.

What causes genetic mutations Some mutations are caused by errors of the genetic machinery which are known as spontaneous mutations. Mutations can also come from exposures to mutagenic agents which are known as induced mutations. Examples of mutagenic agents are UV radiation, cosmic rays, X-rays and some chemicals. Skin cancer has been on the rise for the past few years because of the depletion of the Earths Ozone layer. UV light is able to penetrate through the Ozone which causes point mutation in humans because of its high frequency. According to recent studies it is now predicted that one of every nine Canadians will develop skin cancer. Cancer is considered to be a genetic mutation because it is always a result of a mutation in the genetic sequence. Cystic fybrosis is another example of a genetic disease/mutations. It is caused by 60 different types of mutations in the CFTR gene.

Youtube video: Mutations in DNA crash course http://www.youtube.com/watch?v=eDbK0cxKKsk

Mutation animation and quiz : Mcgraw Hill http://highered.mcgraw- hill.com/sites/0072552980/student_view0/chapter9/animation_quiz_5.html

References http://www.youtube.com/watch?v=eDbK0cxKKsk Nelson Biology 12 textbook chapter 5.6 http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/genemutation