BIOB51- Lecture 13
Starting on slide 43 lecture 11-12
Example: One allele favoured: Spinal muscular Atrophy
- A condition that affects the nerves in an area of the spinal cord called the anterior horn. These
nerve cells become damaged, breaking the line between the brain and the muscles. As a result,
the muscles can’t be used and become wasted.
- caused by point mutation: M
- 10% of fitness of regular people
- Why is the M allele not being lost?
- You can see this (the rate of a deleterious allele stays the same overtime) if the rate of loss due
to selection = the rate of creation through mutation.
- For this we have the data to see whether the mutation of this gene leading to this phenotype is
efficient to keep the allele frequency at equilibrium point
- 1)relative fitnesses of genotype – fitness of wild type – 1.0
- The fitness of an individual is 1-the selection against them (s M)
- S is the selection coefficient – ranges from 0 to 1 – the closer it is to 0, the lower the selection
against you (fitness of individual = fitness of wild type).
- 2) Equilibrium frequency of M
- If they are at equilibrium then use this formula -> then rearrange to find u.
- The actual data found is that 1.1x10^-4 so the mutation rate is sufficient to maintain M allele at
Sickle Cell Anemia
- A allele produces normal hemoglobin, mutant hemoglobin produce by S allelepoint mutation.
- The effect of S allele is that it produces a normal hemoglobin to become crystallize and produce
sickle shaped cells – cannot carry oxygen well,