quantitative genetics
traits either continuous or discrete(discontinuous) but are controlled by numerous genes
-polygenic and strongly influenced by environment(multifactorial)
discontinuous/discrete
qualitative: only a few easily distinguished phenotypes
- pea shape, either Tall or Dwarf
continuous
quantitative: continuous range of phenotypes
- wide rage of human heights.
threshold traits
quantitative bc involvement of many genes and strong influence of environment.
-either absent or there.
meristic traits
quantitative
- measured in whole numbers
- litter size and bristle number
additive genetic interaction
no dominance between alleles.
two or more genes= a single contribution to final phenotype
ex-wheat color
covariance
relationships between on population variable (phenotype) and another.
regression coefficient
slope of best fit line between two variables
-allows predicting of one variable if you know the other
phenotypic variance
Vp=Vg+Ve+Vge
-generally both genetic and environmental working together.
Vge
Genotypic environment interaction
-different genotypes react differently to changing environments
heritability
proportion of phenotypic variance due to genetic variance
H2
Broad sense heritability.
H2=Vg/Vp
gives us which proportion of the population phenotypic variance is due to variation in genotype in individuals
DOES NOT PREDICT OFFSPRING
h2
narrow sense heritability h2=Va/Vp predicting inheritance of quantitative traits ????Vg=Va+Vd+Vl CAN predict parent to offspring
realized heritability
the amount of heritability actually observed in crosses
estimating heritability needs
slope of parent to offspring regression line
response to selection
slope of regression line estimates
h2
if h2 is less than one
the regression coefficient is less than 1
R
response to selection
R=h2xS
S
selection differential
difference between the mean of the population and the means of the selected parents.
S= R/h2
for selection to occur
- variation in a trait that is at least due partially to variation in genes
- genetic variation in the population under selection
selection limits due to
- loss of additive genetic variance in response to selection
- fitness decrease due to a genetic correlated response
QTL
quantitive trait locus
- a gene or chromosomal region that contributes to the expression of quantitative characteristics
- QTL mapping, Genome wide association studies
