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Published byGary Sparks Modified over 9 years ago
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Evolutionary operator: p`= p 2 +pq; q` = q 2 +pq. For lethal alleles: p`= p 2 +pq; q` = q 2 +pq. Allele frequenses A-p, a - q For Thalassemia evolutionary operator or
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Evolutionary operator with selection - mean fitness Selection in case Thalassemia: W AA =0.89; W Aa =1; W aa =0.2 Selection recessive lethal gene: W AA =1; W Aa =1; Waa=0
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- mean fitness W AA, W Aa, W aa –individual fitnesses Why mean?
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Equilibria points p=0, q=1 - population contains a allele only and on the zygote level the population consist of the homozygotes aa; p=1,q=0 - population contains A allele only and on the zygote level the population consist of the homozygotes A A.
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Equation for equilibria points
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Condition of the polymorphic state
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Superdominance, when a heterozygote is fitter than both homozygotes Superrecessivity, when a heterozygote is les fit than either homozygotes In intermediate cases: W AA W aa W Aa (if W AA < W Aa ) or W Aa W aa W AA (if W Aa < W AA ) The population has no polymorphic equilibria Heterozygote equilibrium states: p>0, q>0
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Lethal allele Let W aa =0 If W Aa > max(W AA,W aa ) =W AA Equilibrium point is polymorphic Previous conditions: W AA =W Aa =1, W aa =0 Condition not so realistic
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Selection against a recessive allele.
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Selection in case Thalassemia W AA =0.89, W Aa =1, W aa =0.2 If W Aa > max(W AA,W aa ) =W AA Equilibrium point is polymorphic Good condition. Note, that can be W AA <1
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Dominant selection(also selection against a recessive allele) Two different phenotypes {AA, Aa}, {aa} W AA =W Aa =1, W aa =1-s W AA =W Aa =1-s, W aa =1 No polymorphic equilibria point
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Haploid selection
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Equilibria points and trajectories
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Selection against a recessive allele. Trajectories.
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Example. Selection against recessive lethal gene
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Fisher’s Fundamental Theorem of Natural Selection Mean fitness increase along the trajectory
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Lethal allele
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max
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Selection against a recessive allele.
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Mean fitness in case Thalassemia W AA =0.89, W Aa =1, W aa =0.2
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W AA =0.50, W Aa =1, W aa =0.2
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Mean fitness calculation and dynamics
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Convergence to equilibria In intermediate cases: W aa W Aa W AA (or W AA W Aa W aa ) The population has no polymorphic equilibria
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Convergence to equilibria Superdominance (overdominance), when a heterozygote is fitter than both homozygotes Superrecessivity (underdominance), when a heterozygote is les fit than either homozygotes
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Blood groups A,B,O –alleles allel enzyme A O B dominance A A AA, AO, = A B B BB, BO, = B O - AB = AB OO = O
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A O B dominance A A AA, AO, = A B B BB, BO, = B O - AB = AB OO = O
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Evolutionary operator
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Simulation
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One-locus multiallele autosomal systems
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Fishers Fundamental Theorem of Natural Selection Mean fitness increase along the trajectory
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