Mutagenesis - 20

what are mutagens?

agents that increase the mutation rate

what is electromagnetic radiation used for?

• x-rays, parts of the UV spectrum can be detrimental

• liner effects of x-rays - surprise at such a small amount of energy having a large effect (first hint of the gene as a tiny part of the cell)

• Muller - concern that no dose of radiation was safe, however small - idea of genetic load

what is an example of radiation having harsh effects?

• Hiroshima & Nagasaki

  • short term -initial survivors suffered from radiation sickness

  • long term - fears of health of follow generations at first sight or have been large at Chernobyl at DNA level at least

where does radiation come from?

• net input - importance of radon gas in the UK, comes largely from granite

• other forms - ultraviolet as a mutagen, leads to formation of thymine dimmers

  • typically repaired by excision enzymes

what does a mutation in the excision mechanism cause?

Xeroderma pigmentosum

what are chemical mutagens?

• mutations in survivors of war gases

• Aflatoxins - surprising mutagens like fire retardants

• many natural substances like black pepper also mutagens

• antimutagens - vitamin C

what is the Ames test?

checks for mutagens (and so, carcinogens) with salmonella

what human diseases are associated with age?

due to a build up in germ line mutations

• an increase in the incidence of achondroplasia, autism and schizophrenia is associated with age of the father

how have mutations been viewed in recent years?

• seen as inevitable property of the genome - certain genes increase the mutation rate in others, while failures of repair enzymes are involved in cancer

• the distinction between somatic and germinal mutations is blurred:

  • some cancers emerge from somatic mutation of the normal allele in an individual who is heterozygous for a recessive alleles that predisposes towards cancer

• molecular bio has made genetics much more complicated