Chapter 21 - Genetics of Complex Traits

• multiple genes

• allele interactions

• environment variation

• allele and environment interaction

what four things influence complex traits?

• number of genes that determine the trait

• genetic and environmental factors that affect penetrance and expressivity of genes

facorts causing continuous variation of quantitative traits

genetic, environmental

one of the goals of quantitative analysis is the separate the ______________ effects from the ______________ effects

heritability

the proportion of phenotypic variance due to genetic variance

broad sense

variability is measured only when comparing identical twins to each other

one

only ____ allele at any given locus is shared

loci

the specific, fixed physical position of a gene or genetic marker on a chromosome

narrow sense heritability

heretibility that looks at the additive variance

genetic relatedness

average fraction of common alleles at all genetic loci shared by relatives 

1.0

if environment had no effect, what would the heritability be?

0

if there was not genetic contribution, what would the heritability be?

0.0

if the heritability is _____, no difference would be observed between monozygotic, dizygotic, or unrelated by adoption

1.0

if heritability is ____, differences WOULD be observed between monozygotic, dizygotic, or unrelated by adoption

selection differential

difference between value for this trait in the parents and valuefor this trait in the entire population 

response to selection

the amount of change in the mean value of a trait that results from selection

quantitive trait loci

genes that contribute to complex traits (QTLs)

direct QTL mapping

requires crosses between individuals that differ in the phenotypes of interest

looks for joint segregation of the phenotype and genetic markers

association mapping

takes advantage of the history of a random breeding population

DNA markers

things such as SNPs, insertions, deletions, of SSRs that segregate with phenotype

near

markers strongly correlated with phenotype are likely to be ________ genes that influence the trait

correlation with phenotype

how are QTLs identified?

genome wide association studies

• has identified genes that control only a fraction of the total trait variation 

• recent variation has not spread widely around the globe 

• you need huge amounts of data