S13) DNA Mutations Flashcards
What is a mutation?
A mutation is a change in a DNA sequence
Describe 4 ways in which mutations can arise
- DNA replication errors during cell division (mitosis and meiosis)
- Exposure to ionising radiation (mutagens)
- Exposure to chemicals (chemical mutagens)
- Infection by viruses
Distinguish between a somatic mutation and a germ line mutation
- A germ line mutation occurs in the eggs/sperm, affecting all cells in the body and can be passed on to offspring
- A somatic mutation occurs in a somatic cell and is not passed on to offspring
Why are RNA translation errors not as severe as errors in the genome?
- RNA errors are unlikely to occur repeatedly in the same place
- RNAs are quickly degraded
- RNAs are not inherited molecules passed down to offspring
Mitochondrial DNA is also prone to somatic mutations, which are not inherited.
Why are mitochondrial somatic mutations often severe?
- mtDNA has a limited ability to repair itself so mutations accumulate over time
- mutations of mtDNA are associated with forms of cancer and an increased risk of age-related disorders e.g. heart disease, Alzheimer’s Parkinson’s
With reference of autosomal dominant and recessive disorders respectively, outline the possibility of spontaneous mutations
- In an autosomal dominant disorder, e.g achondroplasia, if a parent is not affected then a spontaneous mutation has occurred in the affected child
- In an autosomal recessive disorder, e.g cystic fibrosis, if no heterozygous/homozygous parents, then a spontaneous mutation of the same gene on both chromosomes has occurred (incredibly unlikly)
Classify germ line mutations in terms of macro and micro mutations.
- Micromutations (gene): substitution, insertion, deletion
- Macromutations (chromosome):
I. Structural - deletion, duplication, inversion, translocation
II. Numerical - non-disjunction
Explain why the mutation rate in male gametes is approx. 5x higher than in female gametes
- The number of germline divisions in spermatogenesis vastly exceeds that in oogenesis
- Spermatogonial germ cells are continually active in adult men and the male mutation rate increases with age
Why do male and female gametocyte mutations increase with age?
- Spermatozoa are continually made
- Older spermatagonia have been exposed to mutagens/radiation for a longer time
What do you think are the possible outcomes if a very early embryo was exposed to radiation?
- Death/aborted
- Teratogenesis
- Cancer when born
Which 4 features enable a germ cell mutation to be inheritable?
- Not lethal to the gamete
- Does not impair gamete function
- Not lethal at fertilisation
- Allows for the production of a viable adult with normal reproductive capacity
In terms of their respective effects, describe the general trends observed in recessive and dominant mutations
- In general, recessive mutations cause loss of function and often affect biochemical pathways
- In general, dominant mutations cause increased function and often cause structural abnormalities
In terms of mutations in proteins, explain why there is an increased incidence of recessive mutations
A given mutation is much more likely to be deactivating/inactivating than introduce a new function because there are far more ways to deactivate/ inactivate a protein
In terms of the trends seen in protein mutations, account for the varying effects amongst recessive and dominant mutations
- Reccesive mutation: if heterozygous, failure of one allele to produce a protein can be compensated for by the normal allele, thus masks the effect
- Dominant mutation: if heterozygous, overproduction by a single allele cannot be ‘compensated for’ by the other normal allele, thus produces an effect
How do somatic mutations arise?
- Mutagens
- Radiation
- Viruses
