Powerpint mutation


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Powerpint mutation

  1. 1. SOURCE OF VARIATION: MUTATION<br />Is a change in a gene orchromosome<br />
  2. 2. 14<br />Mutations<br />A mutation is a spontaneous change in a gene or <br />chromosome<br /><ul><li>Gene mutations may arise when a gene fails to make an exact</li></ul>copy of itself during replication prior to meiosis or mitosis<br /><ul><li>Chromosome mutations can result from:</li></ul>-Damage to, or loss of a chromosome<br />-Incomplete separation of chromosomes at meiosis leading to<br /> extra chromosomes in one gamete<br />-Part of a chromosome becoming attached to another chromosome<br /> (translocation)<br />- Doubling the whole set of chromosomes<br />
  3. 3. 22<br />Chromosome mutations in humans usually result in spontaneous <br />abortion of the foetus<br />But a proportion survive e.g.<br />Downs syndrome: The affected person has one extra chromosome<br /> in their genome (i.e. 47 instead of 46 chromosomes) <br />This results in characteristic facial features, varying degrees of <br />mental impairment and, usually, a very cheerful disposition<br />Klinefelters syndrome. The affected male has an extra <br />X chromosome (XXY)<br />The person appears to be a normal male but he is infertile<br />Chromosome mutations in humans<br />
  4. 4. 25<br />-A mutated gene which is dominant, or inherited as a homozygous<br />recessive, will affect the whole organism<br />-A mutated gene which does not result in abortion or early death<br />of an organism will be inherited by the offspring <br />-Very rarely, a mutation will be beneficial and will be inherited by<br />the offspring<br />Gene mutations in humans may result in:<br />Albinism<br />Sickle cell anaemia<br />Haemophilia<br />Cystic fibrosis<br />Dwarfism<br />Colour blindness<br />Mutations<br />
  5. 5. 26<br />-If a gene mutation takes place in a gamete which contributes to<br />a zygote, the mutation will affect the whole organism<br />-A gene mutation in a body cell will affect only that cell and <br />any cells derived from it.<br /><ul><li>It is mutations in body cells which give rise to cancers.</li></ul>-These mutations usually affect the genes which control cell division<br />-The control on cell division is reduced so that the cell divides<br />repeatedly, giving rise to a tumour <br />
  6. 6. 30<br />Mutagens<br />Some environmental effects may increase the mutation rate.<br />These include radiation (X-rays, ultra-violet, radioactive materials) and carcinogenic chemicals such as those in tobacco smoke<br />These are all known as mutagens<br />-Mutagens which affect body cells may produce cancers. <br />-Mutagens affecting the reproductive organs may result in defective offspring<br />
  7. 7. Question 1<br />35<br />Chromosome mutations can occur as a result of…<br />(a) gain of an extra chromosome<br />(b) doubling of the entire set of chromosomes<br />(c) faulty replication of DNA<br />(d) breaking of a chromosome<br />
  8. 8. 36<br />Question 2<br />Gene mutations can occur during DNA replication<br />prior to …<br />mitosis<br />(b) meiosis<br />
  9. 9. Question 3<br />37<br />Sickle cell anaemia results from …<br />a change in a nucleotide triplet<br />(b) a change in a single nucleotide<br />(c) a change in a single amino acid<br />(d) a chromosome mutation <br />