Lecture 3

Question 0

Developmental Epistasis

Answer 0

Development is not linear, very complex interaction

Eg corn. Depend on the layer of the corn kernel
Pericarp is clear
Aleurone is purple dominant or clear recessive
Endosperm is yellow dominant and clear recessive

Purple is epistatic to yellow
Nothing to do with the chemical interaction, but dependent on where the genes are expressed.

Ordering genes in a developmental pathway. Not dealing with biochemical pathway

Ethylene, change plant as hormone. In this case, it makes elongated plant into short plant

Recessive mutation effects

Constitutive triple response,fooled into thinking that ethelen is present even thigh ethylene is not present. Eg, CTR is a negative regulator, like a break which prevents a response. Lose it, things happen, negative regulator

Blind, insensitive, there is stimulus but appears not to respond
So the gene involved in positive regulator.eg. Ert1, EIN2 is needed for response.

Mirror image

So what happen if we do double mutant, which are mirror images, there only three problems.
1. Insensitive
2, constitutive
3, in between

Cross between CTR and ert
CTR is Epistasis to ert

Ein2 and CTR, we find ein2 is Epistasis to CTR

We did genetics and found before they were discovered the biochemistry caught up.

We can form a developmental pathway
Ert was a receptor
CRT is a kinase
Ein2 turn on genes

Ert is GENETICALLY upstream, not BIOCHEMICALLY upstream

Question 1

Chemical Epistasis

Answer 1

Law independent is genes
Law of segregation is alleles

Chemical Epistasis

3 to on 1 generate 9:3:3:1
But through Epistasis, it is a linear pathway, 9:3:4 as the pathway involves gene masking of the phenotype.

When masking occurs, if a precedes b in a pathway, a is Epistasis to b
Recessive Epistasis

Btu there are more than one type of Epistasis, for example, complementary Epistasis

Eg. A and C

Note though the prevalence of phenotype does not indicate the biochemistry. However the biochemistry does indicate the phenotype.