14) Heritability Flashcards
What actually determines phenotype?
Not actually genes themselves, but gene EXPRESSION
2 more phenomena which help determine which phenotype are expressed:
1) Epigenetics
2) Environment
What is epigenetic?
Nucleus: DNA is wrapped around histone proteins= Form Chromatin
Either DNA or histones can be ‘tagged’ with small molecular groups e.g. Acetyl groups
Can switch genes on or off= Control which allele is expressed
Tags can also be passed from parents to offspring= Heritable but is NOT DNA
What is an example of epigenetics?
Agouti gene= Mice coat colour
A= Recessive
It is partly recessive because it has an epigenetic tag on it= DNA is methylated
In some circumstances the tag can be removed= Yellow
2 features:
1) Tag can be passed onto offspring BUT whether or not the tag is removed is depend on whether chromosome that its on is packed into sperm or eggs= Inheritance patterns change
2) Many of epigenetic tags are RESET during meiosis in response to cell’s environment= could be due to parent’s health
What is the effect of environmental effects on phenotype?
Developmental mechanisms that produce phenotypes from genotypes are sensitive to environmental factors e.g. smoking causes cancer, processed foods cause diabetes)
Environmental effects: Act to increase the variability of the phenotype produced by a genotype
How much of a role do genes play in a trait?
Nature vs Nurture
Problem: Continous traits are a problem e.g. height and weight as they can vary a lot
Heritability: Proportion of phenotype variation that is due to genetic variation
Easiest way to estimate it= Plot the phenotype of offspring against mean parental phenotype, if low heritability= Data points will spread far out
High heritability= Straight line
Can use heritability to see whether or not should be looking at ‘gene responsible’ or environmental factors
GWAS: Attempts to link particular regions of DNA with particular traits in large populations
