EB7 - no equations Flashcards
What is selection needed for
to maintain adaptation against deleterious mutations
the more deleterious the allele
the greater s and the lower the frequency
What happens if there is no selection against the mutation A->B in a unidirectional model
all with become B
What is hypothesized to be important for selection to be effective in removing deleterious alelles
the fitness differences must be greater than the mutation rate
Why does the mutation rate need to be low for selection to be effective?
for selection to be effective mutation rates need to be low or mutations would keep occurring.
What can the mutation selection balance explain
why many chromosomes in Drosophila and humans carry rare mutations that slightly reduce fitness in heterozygotes but are strongly deleterious in homozygotes
What is an example of mutation selection balance
spinal muscular atrophy
SMA
** second most common disease in caucasians after C|F
what is SMA and what is it caused by
a neurodegenerative disease; weakness and wasting of muscles.
caused by loss of function of telSMSN locus it is a lethal autosomal recessive
how can we calcualte the frequency of loss of function allele and what is the selection coeff estimated at
know it affects 10,000 newborns so can calculate frequency as q =0.01
s = 0.9 est.
How can mutation selection balance explain why SMA alllele is maintained at a high frequency
recessive so q’= SQRT(u/s)
therefore (0.01)^2 x 0.09 = 0.910-4
estimated from no. of patients due to new mutations = 1.110-4
The rate of mutation estimated from equation and directly from patients is simialr which suggests selection mutation balance
what is the estimated mutation rate for new mutations in patients
7/340 due to new mutations
u = 1.1*10-4
What effect does selection coef have on the expected no. of carriers
decreases the higher the selection coef
what is the total no. of carriers of a mutation before it goes extinct equal to
inversely proportional to the magnitude of its deleterious effects (i.e the selection coeff)
Why do strongly delterious mutation disappear quickly
more deleterious the mutation, the lower its persistence through generations the fewer the no. of carriers, therefore strongly deleterious mutations disappear quickly, midly persist.
What can genetic diseases be due to, what does this suggest and what does this mean
can be inherited from a parent or due to a new mutation
-if this is the case likely to be bad simply because disease has killed of previous carriers
means can estimate the selection coeff from the proportion of cases where neither parent has the disease
