Genetics 4: Epigenetics Flashcards
How is the phenotype of an individual determined
Interactions between alleles at the same and in many cases, number of different loci as well as the environment
What is Pleiotropy and give example
A single gene having multiple phenotypic effects
Eg. CFTR gene : defective Cl- transport channels: cannot regulate movement of water across cells. Causes: Chronic bronchitis. Poor absorption of nutrients in intestine. Block pancreatic and bile duct.
What is Epistasis and give example
When one gene/locus affects the phenotype of another.
Eg. Colour of dog coat determined by one locus (having different alleles for different colours.
+ Whether colour can be deposited on hair has two genes (y/n)
So there is a dominant and recessive gene at each locus and each of these will determine
Why does epistatic genes lead to non mendelian inheritance 9:3:4 inheritance rather than 9:3:3:1 ratio
Despite the dominant alleles present for one gene, the other gene nulls out that effect
What type of inheritance is behind Quantitative/continuous traits
Polygenic inheritance: the additive effect of two or more genes that determine a single phenotypic character.
How do you explain the quantitive trait of skin colour
3 genes A,B and C have dominant and recessive versions and exhibit incomplete dominance so combinations of these can lead to the same colours leading to a bell curve of colours, that environmental actors can help to smooth the curve.
What effect does the environment have on the phenotype
This can lead to departure from Mendelian inheritance. A range of phenotypes (emergent unpredictive properties) result from single genotype interacting with different environments
What is the norms of reaction, what does it effect the most
The phenotypic range of a given genotype in different environment. Therefore it measures quantitatively the environmental impact on the phenotype.
It is most relevant for polygenic characteristics which will have a larger breadth
Show how the environment effects the eye size of drosophila
Three genetic types : Wild, infrabar and Ultrabar are determined by range of number of facets of eye. However within different temperatures, it shows a norm of reaction- the number of facets within a certain type has a decreasing relationship with temperature. Or increasing temperature.
What is developmental noise
Random events in developmental process that generates the phenotype leads to variation in a phenotype even when exposed to the same environment and same genotype.
What is Epigenetic landscape proposed by Conrad Waddington and how does it tie the genetic concepts together
How we think of translation of genotype to phenotype.
As a developing organism we start at the top of the hill and roll down the landscape. The path we take is shaped by the gene landscape and environmental factors can push the ball to be biased toward one direction or the other. The path it takes down the hill isn’t perfectly straight as well - noise .
What is the concept of epigenetic amplification
Small changes very early on in development can have very large effects as it can exclude many phenotypic outcomes early on.
