2MUTATION 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 inIn some cases, the mutation is not advantageous or lethal to the organism. It is a neutral mutationVERY 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
3MUTATIONA 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 offspringA mutation in the DNA material affects cell activity, because a change in the base sequences alters protein production.
4Types 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.
5Types of Mutations A Change in DNA Sequence: Most mutations are a change in the DNA sequenceThe smallest type is a point mutation, where only one base changesLarge changes can alter the shape of the chromosome:DELETION: Some of the DNA is lost from a chromosomeDUPLICATION: A section of the chromosome is copied on the same chromosome; that is, the same section of DNA appears twiceINVERSION: A section breaks off and is reattached the wrong wayTRANSLOCATION: A piece of DNA from one chromosome breaks off and attaches to a neighbouring chromosomeAMPLIFICATION: A section of DNA is repeated many times; it is a form of duplication, except many more copies
6Discuss evidence for the mutagenic nature of radiation Mutagens are environmental factors that increase the rate of mutationEffect of radiation on DNA strands:E.g. UV light, X-rays, radioactive materialsCan cause bases to be deleted, totally removed from strandCan cause thymine bases to link togetherThis causes a disruption in the normal functions of DNAHigh-energy radiation levels can actually break up the whole chromosome
7Discuss 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 cancerFirst 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 quicklyPeople 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.