lecture 10 Flashcards
what is epistasis
the interaction between two or more genes that control a single phenotype
the allele of one gene masks the phenotypic effect of an allele of another gene
recessive epistasis cc has what ratio
9: 4 :3
why is the albino c gene epistatic to all other coat genes
recessive loss of function mutation in tyrosinase so this means no pigments are synthesised at all
dominant epistasis has what ratio W
12:3:1
why is W (dominant white/spotting) epistatic to all other coat colour genes (minus albino)
loss of function mutation in ckit receptor required to help melanocytes migrate to the hair follicle. inactive dimer
penetrance
measures the percentage of individuals with a given genotype who exhibit the expected phenotype
expressivity
measures the extent to which a given phenotype is expressed at the phenotypic level
incomplete penetrance
some indiviudals don’t show the phenotype at all. all the individuals have the same gene mutation but not all express the phenotype
variable expressivity
sll the individuals have the same gene mutation and display the phenotype, but how strongly the phenotype is expressed is different between individuals
what is the two hit hypothesis
both mutations must occur to get the disease/tumour
eg first hit before birth and second during growth
what is allelic variation
alleles may vary in the severity of phenotypes they cause
what is epigenetic
inherited changes in gene function not caused by mutation eg environment
what are epigenetic tags
dna methylation and histone modification to alter chromatin strcutre . changes the structure of dna but is not a mutation
what is paternal imprinting
the paternal allele is imprinted on by a genetic tag and silenced. the maternal allele is preferentially expressed in the embryo
what is maternal imprinting
the maternal allele is imprinted on by epigenetic tags and silenced. the paternal allele is preferentially expressed in the embryo
