Molecular Biology Flashcards
What is the definition of a mutation
A change in the genetic material of a cell or virus
What is the definition of a gene
A genomic sequence directly encoding for functional products (proteins or RNA)
What is a De Novo mutation
Mutations present in your genome but not your parents.
What causes mutations
Replication/repair errors, metabolism, ionizing radiation, mutagens in food.
Where do De Novo mutations happen
In the parents germ cells or in the early stages of embryogenesis
How can net DNA mutation rate be lowered
Decreasing the rate of DNA damage or increasing the DNA repair efficiency.
Why do most mutations not affect the phenotype
- Most mutations fall in unimportant regions like between exons or genes
- Most mutations are recessive, so two copies are needed to effect phenotype
- Mutations may be silent or conservative resulting in the same or a very similar protein being produced
Why are mutations not typically passed onto the next generation
Only mutations that occur in the germ line cells are passed onto the next generation and the mutation rate in the germ line is a much lower
Why are mutations important for evolution
Natural selection relies on variation, which is acquired through sex and spontaneous mutations
How much of the genome codes for phenotypic traits
1-2%
What are the different outcomes of point mutation?
- Silent- A change in an nucleotide that does not result in a different amino acid
- Nonsense- Change results in a stop codon
- Missense: Change in nucleotide which results in a different amino acid being produced, this can be conservative: amino acid replace with a chemically similar one, or nonconservative: amino acid changed with a chemically different one.
Why do recessive mutations require inbreeding to show?
Recessive mutations must have a copy on both alleles, it would be very rare for someone else to mutate the exact same so they must both come from one ancestor
How do recessive mutations affect gene products
Recessive mutations are usually loss of function mutations, so protein functions worse than before
How can a recessive mutation effect a phenotype
Through having too little product or too much substrate in the pathway of the mutated protein
What type of mutation is albinism and how does it effect phenotype
Albinism is a recessive, loss of function mutation. The phenotype arises due to too little product.
The mutation effects the protein tyrosinase which controls the pathway between tyrosine and melanin. Tyrosinase is working less than normal resulting in too little melanin, which causes the white appearance.
What type of mutation is phenylketonuria and how does this effect the phenotype?
Phenylketonuria is a recessive, loss of function mutation. The phenotype is caused by too much substrate. The mutation effects phenylalanine hydroxylase which controls the pathway between phenylalanine and tyrosine. Phenylalanine hydroxylase functions less that normal so there is a build up of phenylalanine which is converted to phenylpyruvic acid. Too much phenylpyruvic acid leads to progressive brain disfuction. This can be diagnosed using a birthtest and treated with a low phenylalanine diet.
What is incomplete dominance?
When having one mutated allele is enough to show the phenotype but having two mutated alleles is worse. When one allele is wildtype, it still contributes to the protein pool.
