Lecture 2: Recessive mutations File Flashcards
What are genetic differences created by ?
Sex (recombination)
Spontaneous mutation
How many new mutations are in a child (compared to parent) ?
100-200
Name the three main origins of spontaneous mutations
- Replication/repair errors
- DNA damaging agents
- Ionising radiaion
DNA damage - repair = ?
DNA damage - repair = Net mutation
How would you increase mutation rate ?
increase amount of DNA damage,
or decrease rate of repair
How do you induce mutation ?
Use chemical mutagens or radiation
how many times more mutations can be made using mutagens
> 1000 fold
Name 2 things that ALL mutagens do
- Damage DNA (cause mutation)
2. cause cancer
Name two unimportant regions
- Between genes
2. Between exons
Most mutations are silent unless ____?
unless they affect the protein coding part of genes (or their expression)
what is a silent mutation?
One base changes, but end protein is the same
Whats is a nonsense mutation?
One base changes and stops protein production (forms a stop codon)
What are the two types of missense mutation?
Conservative and non-conservative
what is conservative missense mutation?
The mutation causes a different final protein, but the protein is in the same group as the original (e.g. acidic)
What is non-conservative missense mutation?
The mutation causes a different final protein, but the protein is in a different group from the original (e.g. alkaline)
Name the two types of frameshift mutations
- Insertion
2. Deletion
Name base modifier chemical mutagen
EMS (point mutations)
Name base analogue chemical mutagen
5BU (point mutations)
Name intercalating agent chemical mutagen
Acridine dyes (Frame-shift)
Thymine dimers are caused by what ?
UV light
Thymine dimers lead to …..
Frame-shift mutations
Give an example of ionising radiation and name the resulting mutations
X-rays, result in chromosomal breaks (deletion, translocation and inversion)
What is aneuploidy?
The presence of an abnormal number of chromosomes in a cell
What causes downs syndrome and what are main phenotypes?
Extra chromosome 21
short stature, mental retardation and susceptible to alzheimers disease
What are the risk factors for downs syndrome ?
Age of mother (<30=0.04%, >35=1.25%)
What causes Xeroderma pigmentosum ?
Mutations in genes for excision repair machinery
What are phenotypes of Xeroderma pigmentosum?
Extreme sensitivity to UV light (exposure causes basal cell carcinoma, metastatic malignant melanoma and squamous cell carcinoma)
What is the only way for recessive mutations to show in phenotype?
If two carriers mate (requires some form of inbreeding)
What type of mutation can be cured and how ?
Recessive mutations can be cured by gene therapy (inserting wild type version of the gene)
Can dominant mutations be cured by gene therapy ?
Nope lol
What causes albanism ?
mutant tyrosinase enyzme is unable to convert tyrosine to the pigment melanin
What is the albanism phenotype
Melanin absent from skin, hair and eye retinas
What does OCA1 do ?
Codes tyrosinase enzyme (mutants have SEVERE albanism)
What does OCA2 do ?
Codes P protein, a tyrosinase helper (Mutants have MILD albanism)
What does OCA3 do ?
Tyrosine related gene (mutants have WEAK albanism)
What does OCA4 do ?
Codes SLC45A2 protein, a tyrosinase helper (mutants have MILD albanism)
What is alkaptonuria ?
Disorder when gene that encodes homogentisate 1,2-dioxygenase (chromosome 3) mutates
What are alkaptonuria phenotypes?
Mutants cant convert homogentistic acid (black colour) to maleyacetoacetic acid, Mutants expel black urine
What is phenylketonuria ?
Recessive condition, progressive brain dysfunction caused by high phenylpyruvic acid levels
How can you treat phenylketonuria
Phenylpyruvic acid birth test and low phenylalanine diet
What is cretinism ?
Mental retardation caused by thyroid gland not producing enough thyroxine
