MUTATIONS VIDEO

A MUTATION is any change in the arrangement or amount of DNA in a cell or virus. They may occur in SOMATIC (body) CELLS or in GERM LINE (gametes) CELLS Only Germ Line Cell mutations are inherited. Somatic Cell mutations are transmitted, by mitosis, to descendants of that cell only They may occur SPONTANEOUSLY but the rate of mutation is increased by exposure to MUTAGENS A MUTAGEN is any factor which INCREASES the rate of mutation:  X-Rays  Ultraviolet Light  Cyclamate  Mustard Gas  Gamma Rays MUTATIONS:  Arise spontaneously and not directed by the environment. The rate can be altered but not the type.  Mutations are persistent. Transmitted through generations without further change. Although possible to further mutate again causing new characteristic or reverting to the old one.  The majority of mutations confer disadvantages on the organisms that inherit them. A useful mutation is very rare. OVERVIEW

GENE MUTATIONS are changes to base pairs They may occur during DNA replication, which is rare, as enzymes usually detect them and then repair them POINT MUTATIONS are mutations where only a SINGLE DNA nucleotide base changes Some mutations can involve a single DNA nucleotide whilst others may involve many. Results in varying consequences for the synthesis of proteins

Mutation where a nucleotide is replaced by another (Eg. Adenine replaces Guanine etc) Important points:  May code for the SAME amino acid (eg. GAG and GAT) and called a NEUTRAL POINT MUTATION as it has no effect  May code for a DIFFERENT amino acid but slightly different FUNCTIONAL protein is produced  May code for a DIFFERENT amino acid resulting in a NON-FUNCTIONAL protein  May code for a STOP codon and shorten the length of the protein making it NON-FUNCTIONAL SUBSTITUTION

A mutation when 2 or more nucleotides REVERSE their positions Eg. GAG  AGG or ATG  AGT May result in the production of a slightly different FUNCTIONAL or NON-FUNCTIONAL polypeptide INVERSION

A mutation involving the ADDITION of nucleotides in a gene sequence Has a major effect on the sequence as the order after the mutation is ALL altered. This is called a FRAMESHIFT MUTATION Eg. AGG TAC GGG TTC ATG GTA CGG GTT C INSERTION

A mutation involving the DELETION of nucleotides in a gene sequence Generally similar consequence to an addition frameshift mutation Eg. AGG TAC GGG TTC AGT ACG GGT TC Cystic Fibrosis (CF) – codon from 499 th amino acid in the CFTR protein is deleted DELETION

Large structural changes can occur to chromosomes during meiosis These changes are usually visible through a microscope, unlike most gene mutations Duplications and translocations tend to have harmful, often lethal, effects. With inversions and translocations, where there is reciprocal exchange between non-homologous chromosomes, all the genes are nontheless present in normal amounts.

Deletions When a chromosome breaks in 2 places and the middle section drops out The 2 ends then re-join, missing the middle piece Eg. Cri-du-chat Syndrome (5 th Chromomsome) SEE DIAGRAM BELOW Inversions When chromosome breaks in 2 places and the middle section rotates 180° and then re-joins SEE DIAGRAM BELOW

Translocations When a section of a chromosome breaks off and attaches to another chromosome Eg. Segments of chromosome 14 & 8 causing cancer Duplications When a section of a chromosome replicates so that a set of genes repeats Eg. Fragile X Syndrome  repeats of 3 nucleotides on the X- chromosome  instead of 29 repeats = 700+ repeats

Aneuploidy Additions or losses of chromosomes from a cell Caused by NON-DISJUNCTION when 2 homologous chromosomes come together but, instead of separating. Go into the same cell The presence of an extra chromosome is called a TRISOMY. When a chromosome is missing it is called MONOSOMY Eg. Trisomy 21 (Down’s Syndrome) Klinefelter’s Syndrome Polyploidy When cell division fails, all the chromosome set may end in one gamete which may fuse to produce a TRIPLOID individual When 2 diploid gametes fuse a TETRAPLOID individual results Polyploidy is common in plants but fatal in humans

VIDEO: BOZEMAN MUTATION

Sex Chromosome Abnormalities Genotype Sex Syndrome Physical Traits XXY, XXYY, XXXY male Klinefelter syndrome sterility, small testicles, breast enlargement XYY male XYY syndrome normal male traits XO female Turner syndrome sex organs don't mature, sterility, short stature XXX female Trisomy X tall stature, learning disabilities, limited fertility