Transcript ppt

II. Deviations from HWE
A. Mutation
B. Migration
C. Non-Random Mating
D. Genetic Drift - Sampling Error
E. Selection
1. Measuring “fitness” – differential reproductive success
II. Deviations from HWE
A. Mutation
B. Migration
C. Non-Random Mating
D. Genetic Drift - Sampling Error
E. Selection
1. Measuring “fitness” – differential reproductive success
a. The mean number of reproducing offspring (or females)/female
II. Deviations from HWE
A. Mutation
B. Migration
C. Non-Random Mating
D. Genetic Drift - Sampling Error
E. Selection
1. Measuring “fitness” – differential reproductive success
a. The mean number of reproducing offspring (or females)/female
b. Components of fitness:
II. Deviations from HWE
A. Mutation
B. Migration
C. Non-Random Mating
D. Genetic Drift - Sampling Error
E. Selection
1. Measuring “fitness” – differential reproductive success
a. The mean number of reproducing offspring (or females)/female
b. Components of fitness
- probability of female surviving to reproductive age
II. Deviations from HWE
A. Mutation
B. Migration
C. Non-Random Mating
D. Genetic Drift - Sampling Error
E. Selection
1. Measuring “fitness” – differential reproductive success
a. The mean number of reproducing offspring (or females)/female
b. Components of fitness
- probability of female surviving to reproductive age
- number of offspring the female produces
II. Deviations from HWE
A. Mutation
B. Migration
C. Non-Random Mating
D. Genetic Drift - Sampling Error
E. Selection
1. Measuring “fitness” – differential reproductive success
a. The mean number of reproducing offspring (or females)/female
b. Components of fitness
- probability of female surviving to reproductive age
- number of offspring the female produces
- probability that offspring survive to reproductive age
II. Deviations from HWE
A. Mutation
B. Migration
C. Non-Random Mating
D. Genetic Drift - Sampling Error
E. Selection
1. Measuring “fitness” – differential reproductive success
a. The mean number of reproducing offspring (or females)/female
b. Components of fitness
- probability of female surviving to reproductive age
- number of offspring the female produces
- probability that offspring survive to reproductive age
c. With a limited energy budget, selection cannot maximize all three
components… there will necessarily be TRADE-OFFS.
E. Selection
1. Measuring “fitness” – differential reproductive success
2. Relationships with Energy Budgets
E. Selection
1. Measuring “fitness” – differential reproductive success
2. Relationships with Energy Budgets
GROWTH
METABOLISM
REPRODUCTION
E. Selection
1. Measuring “fitness” – differential reproductive success
2. Relationships with Energy Budgets
Maximize probability of survival
Maximize reproduction
GROWTH
GROWTH
METABOLISM
REPRODUCTION
METABOLISM
REPRODUCTION
E. Selection
1. Measuring “fitness” – differential reproductive success
2. Relationships with Energy Budgets
Trade-offs within reproduction
REPRODUCTION
METABOLISM
REPRODUCTION
METABOLISM
Lots of small, low
prob of survival
A few large, high
prob of survival
E. Selection
1. Measuring “fitness” – differential reproductive success
2. Relationships with Energy Budgets
3. Modeling Selection
3. Modeling Selection
Selection for a Dominant Allele
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
= 1.00
3. Modeling Selection
Selection for a Dominant Allele
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
prob. of survival (fitness)
0.8
0.8
0.2
= 1.00
3. Modeling Selection
Selection for a Dominant Allele
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
prob. of survival (fitness)
0.8
0.8
0.2
Relative Fitness
1
1
0.25
= 1.00
3. Modeling Selection
Selection for a Dominant Allele
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
prob. of survival (fitness)
0.8
0.8
0.2
Relative Fitness
1
1
0.25
Survival to Reproduction
0.16
0.48
0.09
= 1.00
3. Modeling Selection
Selection for a Dominant Allele
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
prob. of survival (fitness)
0.8
0.8
0.2
Relative Fitness
1
1
0.25
Survival to Reproduction
0.16
0.48
0.09
= 1.00
= 0.73
3. Modeling Selection
Selection for a Dominant Allele
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
prob. of survival (fitness)
0.8
0.8
0.2
Relative Fitness
1
1
0.25
Survival to Reproduction
0.16
0.48
0.09
= 0.73
Geno. Freq., breeders
0.22
0.66
0.12
= 1.00
= 1.00
3. Modeling Selection
Selection for a Dominant Allele
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
prob. of survival (fitness)
0.8
0.8
0.2
Relative Fitness
1
1
0.25
Survival to Reproduction
0.16
0.48
0.09
= 0.73
Geno. Freq., breeders
0.22
0.66
0.12
= 1.00
Gene Freq's, gene pool
p = 0.55
q = 0.45
= 1.00
3. Modeling Selection
Selection for a Dominant Allele
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
prob. of survival (fitness)
0.8
0.8
0.2
Relative Fitness
1
1
0.25
Survival to Reproduction
0.16
0.48
0.09
= 0.73
Geno. Freq., breeders
0.22
0.66
0.12
= 1.00
Gene Freq's, gene pool
p = 0.55
Genotypes, F1
0.3025
= 1.00
q = 0.45
0.495
0.2025
= 100
3. Modeling Selection
Selection for a Dominant Allele
Δp declines with each generation.
3. Modeling Selection
Selection for a Dominant Allele
Δp declines with each generation.
BECAUSE: as q declines, a
greater proportion of q
alleles are present in
heterozygotes (and invisible
to selection). As q declines,
q2 declines more rapidly...
3. Modeling Selection
Selection for a Dominant Allele
Δp declines with each generation.
So, in large populations, it is
hard for selection to
completely eliminate a
deleterious allele....
3. Modeling Selection
Selection for a Dominant Allele
Δp declines with each generation.
Rate of change depends on the strength of selection; the
difference in reproductive success among genotypes.
In this case, a new
adaptive mutant
allele has been
produced in the
population. The
“selection
differential”, s, is
selection AGAINST
the existing allele
that had become
‘fixed’ in the
population (f = 1.0)
So, the “better” the
new allele is
(represented by the
greater selective
differential against
the old allele), the
faster the new
mutant
accumulates in the
population.
3. Modeling Selection
Selection for a Dominant Allele
Selection for an allele where there is not complete
dominance:
- Consider incomplete dominance, codominance,
or heterosis. In these situations, the heterozygote has a
phenotype that differs from either of the homozygotes,
and selection can favor one genotype over another:
- Selection might favor one homozygote over the
heterozygote and other homozygote (first example), or
might favor the heterozygote over the homozygotes
(second example), or might favor both homozygotes
over the heterozygote (not considered here).
Selection for the homozygote of a ‘non-dominant’ allele
(incomplete dominance, codominance, overdominance)
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
prob. of survival (fitness)
0.8
0.4
0.2
Relative Fitness
1
0.5
0.25
Survival to Reproduction
0.16
0.24
0.09
= 0.49
Geno. Freq., breeders
0.33
0..50
0.17
= 1.00
Gene Freq's, gene pool
p = 0.58
Genotypes, F1
0.34
= 1.00
q = 0.42
0.48
0.18
= 100
Selection for the homozygote of a non-dominant allele
- deleterious alleles can no longer hide in the
heterozygote; its presence always causes a reduction in
fitness, and so it can be eliminated from a population (if
the heterozygote is less ‘fit’ than the AA).
Selection for the heterozygote
p = 0.4, q = 0.6
AA
Aa
aa
Parental "zygotes"
0.16
0.48
0.36
prob. of survival (fitness)
0.4
0.8
0.2
Relative Fitness
0.5 (1-s) 1
0.25 (1-t)
Survival to Reproduction
0.08
0.48
0.09
= 0.65
Geno. Freq., breeders
0.12
0.74
0.14
= 1.00
Gene Freq's, gene pool
p = 0.49
Genotypes, F1
0.24
q = 0.51
0.50
0.26
Maintains both genes in
the gene pool
peq = t/s+t
= 0.75/1.25 = 0.6
AA
= 1.00
Aa
aa
= 100
Maintains both genes in
the gene pool
peq = t/s+t
= 0.75/1.25 = 0.6
Selection for the Heterozygote
Sickle cell caused by a SNP of valine for glutamic acid
at the 6th position in the beta globin protein in
hemoglobin (147 amino acids long).
NN
NS
SS
The malarial parasite (Plasmodium falciparum) cannot
complete development in red blood cells with this
hemoglobin, because O2 levels are too low in these
cells.
E. Selection
1. Measuring “fitness” – differential reproductive success
2. Relationships with Energy Budgets
3. Modeling Selection
4. Types of Selection
- Selection acts on phenotypes, which may be single gene traits,
polygenic quantitative traits, and/or effected by epistatic
interactions.
- The different effects are measured by changes in the mean
phenotype over time.
E. Selection
4. Types of Selection - Directional
E. Selection
4. Types of Selection - Directional
E. Selection
4. Types of Selection - Stabilizing
E. Selection
4. Types of Selection - Disruptive
Lab experiment – “bidirectional
selection” – create two lines by
directionally selecting for extremes.
Populations are ‘isolated’ and don’t
reproduce.
E. Selection
4. Types of Selection - Disruptive
African Fire-Bellied Seed Crackers