Quantitative Traits Flashcards
Qualitative vs. Quantitative traits
Qualitative: show Mendelian inheritance, little environmental effect, individuals can be correctly identified from phenotype
Quantitative: variation of phenotype, complex mode of inheritance, moderate to great environmental effect
what is continuous variation? how is it described?
also known as quantitative inheritance
-described in quantitative terms
what are multifactorial, complex, and meristic traits?
Multifactorial: controlled by 2+ genes and show significant interaction with the environment
Complex: relative contribution of genes and environment are not yet established
Meristic: phenotype is recorded by counting whole numbers
mean, variance, standard deviation, and error of mean definitions?
Mean: average of numbers
Variance: average squared distance of all measurements from mean
Standard Deviation: square root of variance
Standard error of mean: errors between means determined for multiple samples
what are polygenic traits?
what type of distribution do they have?
what is an example?
traits where 2+ genes contribute to the phenotype
-bell shaped distribution
-EX: eye and skin color
what is a major or modifier gene
Major: genes influenced strongly by several alleles
Modifier: genes influenced by alleles to a smaller degree than major genes
what is averaging out of phenotype called
regression to the mean
how do mendelian traits explain quantitative traits? what is the phenotypic ratio associated with this hypothesis?
MULTIPLE-GENE HYPOTHESIS: can be explained by many genes, each behaving individually in mendelian fashion, contributing to the phenotype in a cumulative way
-Ratio: 1:4:6:4:1
what is phenotypic variance
divided between genotypic and environmental variance
genetic vs environmental variance
Genetic: variance attributed to genotypic difference
Environmental: variance attributed to difference in the environment
what is a correlation coefficiant
measure the degree to which variables vary together
how does gene-environment interaction affect the potential range of phenotypic values?
it widens the potential range of phenotypic values that may occur
3 types of genotypic variance?
what do they describe?
Additive variance(Va)-additive action of alleles
Dominance variance(Vd)-when phenotypic expression in heterozygotes is not precise
Interactive variance(V1)-when 2+ loci behave epistatically
what are characteristic of discontinuous traits
-non overlapping phenotype classes
-sharply distinguishable categories
what is heritability? what is it symbolized by? what is its range?
describes proportion of total phenotypic variation
-Symbilized by H
-range 0-100(no genetic to control-full genetic control)
broad vs narrow heritability
Broad: measures contribution of genotypic variance to total phenotypic variance
Narrow: proportion of phenotypic variance due to additive genotypic variance alone
T/F broad sense heritability is a more valuable predictor of response to selection
FALSE. narrow is
variance in identical vs fraternal twins
Identical: variance equals only environmental variance
Fraternal: variance equals environmental and genotypic variance
concordance vs discordance
Concordance: percentage of twin pairs where both have the same phenotype
Discordance: percentage of twin pairs where twins have different phenotypes
what is a QTL? how are QTL maps made?
Quantitative Trait Loci: genes that contribute to phenotypic variation in quantitative traits
-maps are made by statistically identifying regions of chromosomes likely to contain QTLs
how are LOD scores and thresholds used for QTLs
LOD: probability of odds with QTL present/probability of odds with no QTL
Threshold: LOD score above certain threshold suggests QTL linked to specific marker
what is a GWAS? how are its results displayed?
Genome Wide Association Studies: look for associations between traits and groups of alleles in populations
-displayed on manhattan plot: higher green bar + stronger association
what was the candidate gene for high association between Crohn’s disease and 16q2.2
CARD15
results showed that an identical ______ base pair insertion at nucleotide 3020 of exon 11 of three of the CD patients: the mutation causes a ________ that results in a _______ codon
C-G
Frameshift
premature stop
narrow sense heritability equation
h^2 = Va/Vp
