non mendelian ratios B

environmental modification

conditions to dictate expression

• phenotype shown/the degree to which it is shown

• ex. sun causing humans to tan/freckle

gene interaction

several genes influence the same trait

non allelic

not controlled by one gene

epistasis

alleles at one locus mask genotype at second locus

complementation

crossing 2 recessive mutants generate wild-type progeny

9:3:3:1 ratio

indicates 2 genes are involved

mutant

different from what is usually found in a population

complementation test

cross mutants to look for wild type in F1 → mutant needs to be a recessive trait

• F1: all progeny show mutant phenotype → mutation is on same gene

  • no complementation because same locus → mutant genes are allelic

• F1: all progeny show wild type phenotype → mutation is on diff gene

  • complementation → mutant genes are not allelic

how to identify

F2 ratio: 9:3:3:1 or some variation → 1 trait controlled by 2 genes

sex linkage

genes on sex chromosomes

heteromorphic

chromosomes have diff shapes

pseudoautosomal regions

allow chromosomes to pair in prophase and have recombination

human sex chromosomes

XX, XY

SRY gene

sex determining region on Y chromosome

homogametic

same sex chromosome (XX)

heterogametic

diff sex chromosome (XY)

nondisjunction

gametes with different number of chromosomes

• could be more/less

• result of mistakes in anaphase

thomas hunt morgan

1st to study sex linked genes in fruit flies

dosage compensation

to correct the imbalance between proteins made by X and Y chromosomes

• females have 2 x chromosomes so they produce double the proteins as males

• solution: ½ female cells activate mom’s X chromosome and the other ½ activate dads X chromosome

tight coiling

how the cells inactivate one chromosome

sex influenced traits

more common in 1 sex

autosomal

being male/female affects whether the allele is dominant/recessive

sex limited traits

expression is limited in one sex → no penetrance in the other

• autosomal

• ex. horns in male cows, never females