G12 Flashcards
what are inherited from parents?
alleles not genotypes
what are the three trait types
continuous - bell curve
meristic - countable
threshold (multifactorial) - enviro and multiple genes
what is continuous distribution due to?
polygenic variation, segregation of multiple independent mendelian loci. phenotype cant be easily predicted from genotype and vv
What does polygenic theory assume?
that genes are additive.
created different additive classes different by one unit and that random environmental variation then created a bell curve.
what is the number of phenotypic classes expected when there are n bi allelic additive genes with equal effect?
2n +1
what are the components of phenotypic variation
Vp = VG+VE VE = estimated if inidividuals of uniform genotypes (VG=0) are grown in different environmental conditions VG = estimated if individuals of different genotypes grown in same envrionmental conditions VE=0
what are the components of genotypic variaition
VG = VA + VD + VI
VA - additivie genetic variance (sum of phenotypic effects of alleles when assembled in genotypes
VD - deviation of genotypic values from their values under the additive gene action due to dominance
VI - deviation of genotypic values under additive gene action due to interaction among loci = epistatic or interaction genetic variance
what are the components of envrionmental variation
VE = VEW + VEC(s) + VEC(t) + VEC(m)
proportion of total enviro variation caused by unknown or tangible causes plus spatial, temporal and maternal.
(common envrionmetn causing individuals to be more similar to each other than individuals reared in different common environments
spatial eg different vials
temporal - different feeding times
maternal - maternal nutrition differs between females
what is genotype environment correlation and how can this be removed as a factor?
when exposure to environmental conditions depends on an organisms genotype.
remove as a factor by randomising vials and environments.
if dont control leads to increase in variation
or lumped in with VG increasing it by 2covGE
VP = VG + VE + 2CovGE
What is VGE
component of phenotypic variation due to genotypic variation in respinse to different environments ie. phenotypic plasticity. (genotype producing different phenotypes in different environments)- estimated or lumped into GE
what is the full equation for Vp
Vp = VA + VD + VI + 2COVG + VEW + VEC(S) + VEC(T) + VEC(M) + VGE
what can be assumed if subcomponents of Vp are missing
that they are assumed to be zero or have been lumped into another category
what does heritability range from?
0-1
what is the equation for broad sense heritability
H2= VG/VP
Portion of total phenotypic variation attributable to genetic effects
(upper case H)
what is narrow sense heritability
offten just heritability
h2 = VA/VP
portion of total phenotypic variation attributable to the sum of phenotypic effects of alleles when assembled in genotypes
main cause of resemblance between relatives.
lower case h
how can variance of components be measured for heritability estimation?
by comparing different classes of relatives and knowing the fraction of genes they share (covariance) - parent offspring regression. and other relatives using ANOVA and twin studies
what is h^2 equal to
=VA/VP = Cov(mp,o)/Var(mp)
no brackets
how do you calculate the slope on a graph in parent offspring regression
covariance of parents and offspring / varaiance - h^2 = slope
slope approximates the heritability of the trait when offspring values are regressed against the average trait in parents
what is the covariance of parents and offspring equal to
the sum of (mp value = mp mean) x (o value - o mean) /N
what is the hertiability if only one parent value is used in parent offspring regression
twice the slope
what are the concordance rates for CF, hypertension, type 1 diabetes, measles in mono and dizygotic twins
CF 100 25
hypertention 30 10
type 1 diabetes 35 6
measles 76 56
what does it mean if MZ concordance rate is significantly higher than DZ concordance rates
there is genetic influence
what type of trait is CF
monogenic trait - 100% concordance in MZ
what does a significant difference but not 100% between mono and di twins concordance rate show?
complex polygenic trait- enviro acting.
