Lecture 6 Flashcards
(16 cards)
What causes complementary gene action?
A pigment precursor is converted into intermediate X
Then, gene C and an enzyme allow the conversion of intermediate X into intermediate Y
Then, gene P and an enzyme allow the conversion of intermediate Y into pigment
This means that pigment production needs both enzyme so if there is a mutant allele at C locus, this will mask the P allele (and vice versa)
What is epistasis?
Genes that affect each other
They usually operate in the same pathway and contribute to the same phenotype
It modifies Mendelian ratio
What is recessive epistasis?
The recessive allele of one gene masks the phenotype of another
What is the ratio that is indicative of complementary gene action?
9:7
CC- colour
Cc- colour
cc- no colour
On a different locus:
PP- colour
Pp- colour
pp- colour
CCpp and ccPP are both no colour but crossing them produces all progeny with colour (CcPp)
Crossing CcPp and CcPp results in 9 coloured and 7 white
What is an example of recessive epistasis?
Mice have AA or Aa (codes agouti pigment) or aa (codes black pigment)
Another gene ‘B’ codes for pigment, Bb or BB means pigment but bb means albino
If the mouse is AAbb, Aabb or aabb, no pigment is produced no matter if the mouse is agouti or black
This is because B masks expression of A but A doesn’t mask the expression of B
What ratio is indicative of recessive epistasis?
Crossing AaBb with AaBb and getting ratio 9:3:4
What is dominant epistasis?
A dominant allele of one gene masks the effect of the genotype of another locus
What is the indicative ratio dominant epistasis?
Crossing AaBb x AaBb and getting the ratio 12:3:1
What is an example of dominant epistasis?
In squashes, AABB is white and aabb is green (crossing of these would give AaBb)
This produces 12 white, 3 yellow and 1 green
How can the example of dominant epistasis in squashes be explained? (AABB is white and aabb is green)
A colourless precursor is converted into a green pigment
If the B enzyme is dominant, it stops this and prevents pigment (if not, green pigment is created)
If the dominant A enzyme is present, the green pigment is turned into yellow but if not, the pigment remains green)
What is duplicate gene action?
Both genes perform the same function (so you can lose one gene but if one of them is present, the function can still be carried out)
Give an example of duplicate gene action
In the shape of wheat seeds, T and V are both triangular dominant but t and v are both ovate recessive
TTVV- triangular and ttvv- ovate
Crossing TtVv with TtVv results in 15 triangular seeds and 1 ovate seed
How can we explain duplicate gene action?
Enzyme T and V both operate at the same place, if at least one is present, the precursor is converted into intermediate X and then enzyme T or V converts intermediate X into intermediate Y (resulting in triangular shape) but if not, it stays as intermediate X
What ratio is indicative of duplicate gene action?
15:1
How can we identify genes that control a trait?
Make mutants that affect the phenotype (only change one gene at one locus) such as mutating blue plants to be white
Take the mutants and cross them with wild types
If all F1 are blue and F2 are 3:1 (blue to white), each one is mutated at one gene
We then cross the mutants with each other to figure out if they mutated at the same or different gene
If crossed and all the progeny is white, they all mutated at the same gene
If crossed and the progeny is blue, this means they are mutated at different loci which means one gene provides what others lack and there are mutations at different genes
