Mutation

MUTATION A mutation is a change in the DNA information on a chromosome Gene mutation produces NEW ALLELES of genes in species and so creates new genetic variation. Three things can happen as a result of a mutation: Most mutations are lethal and kill the cell the mutation takes place in In some cases, the mutation is not advantageous or lethal to the organism. It is a neutral mutation VERY RARELY, a mutation will give an organism a phenotypic advantage. These individuals with the new allele will be at a selective advantage, and be better suited to their environment

MUTATION A mutation in a body cell is called a somatic mutation. This mutation cannot be passed on to offspring. If the mutation occurs in the sex organs, then the mutation will be passed on to offspring A mutation in the DNA material affects cell activity, because a change in the base sequences alters protein production.

Types of Mutations A Change in Chromosome Number: ANEUPLOIDY: Is the case of an abnormal number of chromosomes. Can sometimes occur because chromosomes fail do separate during meiosis. On fertilisation, there will be an abnormal chromosome number; either too little or too much. E.g., Down’s syndrome. POLYPLOIDY: This is the case where a cell, or organism, has one or more extra, complete, sets of chromosomes. If the zygote is polyploid, then the whole organism will be. If it is in a body cell, then it will not spread much. Occurs because chromosomes fail to move to each pole in mitosis. Polyploidy is encouraged in horticulture, as plants with this feature grow larger and stronger than normal.

Types of Mutations A Change in DNA Sequence: Most mutations are a change in the DNA sequence The smallest type is a point mutation, where only one base changes Large changes can alter the shape of the chromosome: DELETION: Some of the DNA is lost from a chromosome DUPLICATION: A section of the chromosome is copied on the same chromosome; that is, the same section of DNA appears twice INVERSION: A section breaks off and is reattached the wrong way TRANSLOCATION: A piece of DNA from one chromosome breaks off and attaches to a neighbouring chromosome AMPLIFICATION: A section of DNA is repeated many times; it is a form of duplication, except many more copies

Discuss evidence for the mutagenic nature of radiation Mutagens are environmental factors that increase the rate of mutation Effect of radiation on DNA strands: E.g. UV light, X-rays, radioactive materials Can cause bases to be deleted, totally removed from strand Can cause thymine bases to link together This causes a disruption in the normal functions of DNA High-energy radiation levels can actually break up the whole chromosome

Discuss evidence for the mutagenic nature of radiation UV radiation has been recorded to increase the incidence of skin cancers in humans. Some regard it as the sole cause of skin cancer First generation radiotherapists, who did not now the dangers of radiation, often died young. Scientists like Marie Curie would carry uranium around in their pockets, and developed cancers very quickly People who live in areas which have been affected by high-level radiation, such as Hiroshima, or Chernobyl, still show high incidences of cancers and other mutations in their offspring.