L6 - departure from mendelian ratios due to gene interaction (epistasis)

Question 1

when can you expect to see mendelian ratios?

Answer 1

when genes affecting same trait operate independently of each other

Question 2

what is complimentary gene action

Answer 2

• when genes act together to produce a phenotype
• homozygous recessive genotype at either locus produces same phenotype

eg PPcc white
CCpp white

Question 3

what is the genotype ratio of complimentary gene action

Answer 3

9:3:3:1

Question 4

what is the phenotype ratio of complimentary gene action

Answer 4

9:7

Question 5

if mutant allele A masks B then?

Answer 5

A is epistatic to B

Question 6

what is recessive epistasis

Answer 6

• 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

Question 7

genotype ratio for recessive epistasis

Answer 7

9:3:3:1

Question 8

phenotype ratio for recessive epistasis

Answer 8

9:3:4

Question 9

what is dominant epistasis

Answer 9

dominant allele of one gene masks effect of other locus

Question 10

genotype ratio for dominant epistasis

Answer 10

9:3:3:1

Question 11

phenotype ratio for dominant epistasis

Answer 11

12:3:1

Question 12

what is duplicate gene action

Answer 12

occurs when both genes perform same action

eg
T - round seed
V - round seed
t/v - triangle seed

Question 13

genotype ratio for duplicate gene action

Answer 13

9:3:3:1

Question 14

phenotype ratio for duplicate gene action

Answer 14

15:1

Question 15

what does it mean if 2 alleles are redundant?

Answer 15

they both have the same function

Question 16

why is complementation test used?

Answer 16

to determine how many genes control a specific trait

Question 17

describe steps that need to be done before complementation test

Answer 17

1. make mutants that affect phenotype that you want to investigate
2. isolate mutants defective in trait of interest
3. make sure mutant is due to change in one gene by crossing each with wild type

Question 18

in a complementation test how can you make sure a mutation is due to only one gene

Answer 18

cross each mutant with wild type
F1 should all be wild type
F2 should be 3:1 ratio

Question 19

describe steps of complementation test

Answer 19

1. 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

Question 20

what does it mean if the wild type is not regenerated in a complementation test

Answer 20

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

Question 21

what does it mean if the wild type is regenerated in a complementation test

Answer 21

the mutations are in alleles of different genes

each mutant provides dominant alleles to ‘cancel out’ the others recessive ones

Question 22

what does number of complementation groups tell us?

Answer 22

the no. of genes that mutated