what does heritability measure
- proportion of the total phenotypic variance among indviduals in a population that is due to differences in their genes
what is the range of heritability? (3)
- it ranges from 0-1
- 0.0 = all differences are due to environment
- 1.0 = all differences are due to genes
parent-offspring regression
- graph of the parent phenotype with the offspring phenotype
- slope of regression (2)
- slope measures extent to which offspring resemble their parents
- essentially heritability
parent-offspring regression
- slope = 0 (2)
- no resemblance
- no response to selection, evolution cannot happen
parent-offspring regression
- slope = 1.0 (2)
- strong resemblance
- strong response to selection, evolution can happen
what is the formula for heritability (by looking at response to selection)
- heritability = R/S
what is S in the formula for heritability (by looking at response to selection) (2)
- selection differential
- s = Xs - Xp
what is R in the formula for heritability (by looking at response to selection) (2)
- response to selection
- R = Xr - Xp
Xs
- mean of the surviving individuals after selection event
Xp
- mean of original population
Xr
- mean of new generation after selection
R = S
- heritability = 1
R < S
- heritability < 1
R > S
- S is not smaller than R in populations
H = 0 (2)
- does not mean that a trait does not have genetic basis
- if all individuals have the same genotype, there will be no variability at that locus even tho there is genetic basis
variability in selfed-lines (identical genotype) (2)
- Vphenotype = Venvironment
- H = 0
variability in selfed-lines (identical genotype) (2)
Vphenotype = Vgenotype - Venvironment
- H > 0
H > 0 (2)
- does not mean that differences among populations are genetic
- individuals that are genetically identical may show variability in different environmental conditions
- why may there be differences in heritability estimates? (2)
- may be due entirely to environmental differences
- genetically identical heterogenous populations raised with maximal conditions will show greater H, but those grown in the more heterogenous environment will have low H
what are heritability estimates valid for?
- only valid for the population (and the time and place) from which they were obtained
phenylketonuria (3)
- genetic recessive disorder
- deficient in enzyme that converts phenylalanine into tyrosine
- if untreated, may develop severe mental retardation
how does environment and heritability affect those with phenylketonuria (2)
- trait has clear genetic basis so heritability should be high, but it is not because it can be controlled by environment
- homozygous individuals who eat low phenylalanine diet and high tyrosine show no symptoms
what are heritability estimastes good for?
- allows us to predict whether a population will respond to artificial or natural selection
