BI210 - Penetrance, Expressivity, and Parental Effects

penetrance

proportion/percentage of progeny that exhibit dominant allele

expressivity

degree to which genotype is expressed

how does penetrance and expressivity affect pedigree charts

reduced penetrance makes some individuals who would normally be affected not show disease

anticipation

form of variable expressivity in which symptoms get worse with each generation

how do lethal alleles affect expression, genotypic, and phenotypic ratios

having two alleles result in spontaneous abortion

• phenotype is not possible

maternal-effect traits

traits controlled by autosomal genes however progeny’s phenotype is determined by mother’s genotype

how do maternal-effect traits happen

lingering gene effects of mom during embryonic development result in expression of her genotype

maternal inheritance

zygote will contain same mitochondria as egg

• any mutation is directly inherited from mother

why can’t men pass on this form of inheritance

sperm only releases DNA

• mitochondria discarded

genomic imprinting

traits controlled by autosomal genes but phenotype is determined by gene inherited from specific parent

epigenetic changes

modifications to DNA that affect packaging/reading through methylation (CH3)

how does methylation affect DNA expression

methylation increase → gene expression decrease

maternal imprinting

mother silenced; father expressed

paternal imprinting

father silences; mother expressed