Lecture 1 Flashcards
What is the outcome of pluripotent cell going down different cell lineages?
Loss of its pluripotency
Each lineage will have the same genotype but different genotypes
What did Muller discover in the 1930’s?
White eye mutation in drosophila, an unusual patchy phenotype
Something is influencing expression of the white gene - as fly is able to make the red gene still
Mutants made using X-ray
How was the phenotype seen by Muller arising?
An inversion produces position effect variegation
White+ gene produces red facets
Inversion places White+ close to heterochromatin, heterochromatin spreads and silences the gene= producing white facets
All due to changes in chromatin packagaing
Outline Brink’s work from 1958
Had two alleles, Rst and Rr, for maize with distinct leaf phenotype.
Rst leads to stippled leaf pattern
Closing homozygotes for both alleles creates stippled F1 ( appears stippled is dominant)
Would expect RrRr F2 to not be stippled but it is (Rst interaction has caused paramutation - changed phenotype of another allele)
The RrRr F2 also now has ability to pass on the stippled phenotype
What is different about the Rst and Rr mutants in the F0’s?
How does this change during breeding?
Rst is methylated whereas Rr is not
All alleles acquire DNA methylation due to interaction with methylated Rst
What epi-mutant was found by Linnaeus?
The peloria mutant of Linaria vulgaris
How was the peloria mutant different?
The flowers had radial symmetry rather then bi-lateral symmetry
What cause was put forward by Coen for the cause of the peloria phenotype?
How was this disproved?
What was found to be the cause?
A mutation in its cycloidea gene (as seen in Antirrhinum majus)
Sequencing of the gene showed no mutations
The cycloidea gene in peloria is heavily methylated, switching off the gene
What was shown in the trans-generational stress response?
Mothers who were pregnant during famine, shown during the hongerwinter of 1944, had children of lower birthweight, especially if the famine occurred early in the gestation period, and these children had a higher rate of obesity and diabetes in later life. The offspring of these children also gave birth to low weight offspring with the same higher incidence of diabetes and obesity even though they were not pregnant during a famine. DNA methylation was shown to be changed due to grandmothers/mothers nutrition.
What is Riggs’ definition of epigenetics?
The study of mitotically and/or meiotically heritable change sin gene expression that cannot be explained by changes in DNA sequence
What is requires for epigenetic changes?
1) Mechanisms to create specific “expression states” that result in differential gene expression
2) Mechanisms that allow these expression states to be maintained during cell division and development
What is a transient change in gene expression?
Signal changes expression state of the gene, but removing this signal causes the expression to revert to its original state
What is seen in epigenetic re-programming of gene expression?
Signal changes expression state of the gene, and removing this signal does not caue the expression to revert to its original state
What are the key players in epigenetic re-programming?
DNA methylation
Histone acetylation
Non-coding RNA’s
(Lots of interplay seen between these players)
Where does DNA methylation occur?
What is it associated with?
On cytosine residues in many eukaryotes
Generally with transcriptional inhibition (when located close to promoter sequences)
Which other nucleotide can be methylated?
Adenine (but not covered due to early state of the field)
