Genes - Lecture 17 - Gene interactions and epigenetics Flashcards
What is epistasis?
The interaction between two or more genes that control a single phenotype
What are the three main types of epistasis?
One mutation affects the phenotype of another mutation
Either mutation presents no phenotype, but both mutations together presents a phenotype
Either mutation have the same phenotype, but the double mutation has a different one
What is the example of epistasis controlling mammal coat colours?
There are four different genes that interact to form the overall appearance of the mammal
A gene = distribution of pigment in hair
B gene = colour of pigment
C gene = whether pigment is expressed
W gene = distribution of pigment in hair and skin
What is recessive epistasis?
When the recessive allele of one gene can hide the expression of all alleles of another gene
What is dominant epistasis?
When the dominant allele of one gene hides the expression of all alleles of another gene
Why, in mammals, is the gene determining the distribution of pigment in skin and hair epistatic to all other coat colour genes?
It involves melanocytes
They are derived from neural crest cells and mover along the dorsolateral axis to the skin
This gene is a dominant loss of function mutation in a transmembrane growth factor receptor
The transmembrane growth factor receptor is needed for the proliferation and migration of these melanocytes
When the gene is active, it deactivates dimers which means melanocytes can’t move to the right place and produce melanin that moves to the right area
What is meant by epigenetics?
Heritable changes in gene expression that don’t involve alterations of the DNA sequence of the genome
Changes in organisms by modification of gene expression instead of a change in the DNA sequence
What is meant by mitotic and epigenetic inheritance of patterns of gene expression?
Environmental factor switches on the expression of red and green genes
Expression of green genes is transient, meaning it’s not expressed in daughter cells of mitosis
Expression of red genes is present in multiple cell divisions. This is a mitotic epigenetic effect
What is meant by meiotic and epigenetic inheritance of patterns of gene expression?
Environmental factor switches on expression of blue gene in oocyte
The expression of the blue gene persists through multiple generations. This is a meiotic epigenetic effect
What is transgenerational epigenetic inheritance?
When epigenetics is carried through generations
EG the exposure happens in the mother at F0, and is passed to the reproductive cells in the foetus
How can chromatin based modifications cause epigenetic effects?
DNA methylation and histone modifications can alter chromatin structure
Chromatin structure affects gene expression
A change in chromatin structure is passed to daughter cells
Methylated histones and DNA act as epigenetic tags and decide whether genes will be expressed or not
What are the two types of genomic imprinting?
Paternal imprinting
Maternal imprinting
What is paternal imprinting?
The paternal allele is imprinted and silenced by epigenetic tags
The maternal allele is preferentially expressed in the embryo
What is maternal imprintign?
The maternal allele is imprinted and silenced by epigenetic tags
The paternal allele is preferentially expressed in the embryo
How is genomic imprinting related to humans?
Paternal imprinting can cause Prader-Willi syndrome
Maternal can cause Angelman syndrome
