L6 - departure from mendelian ratios due to gene interaction (epistasis) Flashcards
when can you expect to see mendelian ratios?
when genes affecting same trait operate independently of each other
what is complimentary gene action
- when genes act together to produce a phenotype
- homozygous recessive genotype at either locus produces same phenotype
eg PPcc white
CCpp white
what is the genotype ratio of complimentary gene action
9:3:3:1
what is the phenotype ratio of complimentary gene action
9:7
if mutant allele A masks B then?
A is epistatic to B
what is recessive epistasis
- involves 2 loci
- when one is homozygous recessive it affects the other, but not vice versa
eg pigment (P) and colour (C)
ppCC - no colour
PPcc - colour
genotype ratio for recessive epistasis
9:3:3:1
phenotype ratio for recessive epistasis
9:3:4
what is dominant epistasis
dominant allele of one gene masks effect of other locus
genotype ratio for dominant epistasis
9:3:3:1
phenotype ratio for dominant epistasis
12:3:1
what is duplicate gene action
occurs when both genes perform same action
eg
T - round seed
V - round seed
t/v - triangle seed
genotype ratio for duplicate gene action
9:3:3:1
phenotype ratio for duplicate gene action
15:1
what does it mean if 2 alleles are redundant?
they both have the same function
why is complementation test used?
to determine how many genes control a specific trait
describe steps that need to be done before complementation test
- make mutants that affect phenotype that you want to investigate
- isolate mutants defective in trait of interest
- make sure mutant is due to change in one gene by crossing each with wild type
in a complementation test how can you make sure a mutation is due to only one gene
cross each mutant with wild type
F1 should all be wild type
F2 should be 3:1 ratio
describe steps of complementation test
- cross all mutants with each other
- if wild type not produced, the recessive mutations represent alleles of the same gene (loss of function of same gene)
- if wild type is reformed the recessive mutations are in alleles of different genes
what does it mean if the wild type is not regenerated in a complementation test
the mutations are in alleles of the same gene
(mutation caused loss of function in same gene)
they both are recessive for a gene so mutation persists
what does it mean if the wild type is regenerated in a complementation test
the mutations are in alleles of different genes
each mutant provides dominant alleles to ‘cancel out’ the others recessive ones
what does number of complementation groups tell us?
the no. of genes that mutated
