Mutagenesis Flashcards
Electromagnetic radiation
X-rays, parts of the UV spectrum are particularly detrimental. Linear effect of X-rays: surprise at such a tiny amount of energy having such 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”.
Effects of radiation at Hiroshima and Nagasaki; in short term initial survivors suffered from radiation sickness; long term fears of the health of following generations, at first sight to have been large at Chernobyl at DNA level at least.
Net input of radiation; importance of radon gas (in the UK, comes largely from granite) compared to others.
Other forms of radiation
Ultraviolet as mutagen; leads to the formation of thymine dimmers. This is typically repaired by excision enzymes. Mutations in the excision mechanism leads to Xeroderma pigmentosum
Chemical mutagenesis
Mutations in survivors of the war gases. The Ames test - checking for mutagens (and hence for
carcinogens) with Salmonella.
Aflatoxin. Surprising mutagens - e.g. fire-retardants; but many natural substances (e.g. black pepper) also mutagens. Antimutagens - e.g. vit C.
Age
Incidence of many human diseases is 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. Queen Victoria’s father Edward Duke of Kent was very old and also the origin of the haemophilia allele.
Mutation as a property of the genome
In recent years, mutation has been seen as being in 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 has also been blurred, for some cancers emerge from somatic mutation of the normal allele in an individual who is heterozygous for a recessive allele that predisposes towards cancer.
Molecular biology has made genetics much more complicated!
