epigenetics Flashcards
darwin
Darwin first conceived the theory of evolution by natural selection, and that adaptive heritable characteristics were passed on from parent to offspring. This led to the publication of “origin of the species”
punnett squares
show the chance of a dominate and recessive gene, specifically an allele being passed from parent to offspring
chromosomea
Out of the 23 pairs of chromosomes we have in ur DNA, 1-22 are called autosomes, and the 23rd is the sex chromosome (XX for females, as here, or XY for males). We inherit one chromosome from each of our parents
alleles
Alleles are alternate forms of a gene inherited one from the father and one from the mother (and so found on corresponding sites on homologous chromosomes). There can be dominant and recessive versions of the gene.
In any combination with the dominant version, it is the one that is expressed. The recessive only expresses in the absence of the dominant.
what do genes show
Genes are responsible for the type of the body they express (e.g., the eye colour). Alleles dictate what the characteristic of that body part is expressed (e.g., blue, brown, green, grey, etc)
autosomal dominant diseases
for example Huntingdon’s. means it is always carried on the dominant gene. Therefore, when one parent has it, it expresses 50% of the time. If both parents have it, there is a 75% chance of the child inheriting.
ketys research
schizphrenia
We can look at concordance for a variety of phenomena by exploring the degree to which individuals are biological related and/or have shared environments.
Individuals who do not have a shared environment BUT have a biological parent who has schizophrenia have a 9x higher chance of developing schizophrenia than is observed in the general population.
fischers twin study
schizophrenia
The concordance rate, the probability that a second twin will develop a disorder if the proband (first examined) twin has the disorder, is commonly used. The concordance rates of schizophrenia for monozygotic twins have been found to be about 40 to 50%, and heritability estimates are around 80%.
4 laws of behavioural genetics
Turkenheimer (2000), Chabris et al., (2015)
- All human behavioural trait are heritable
- The effect of the genes is larger than the effect of the shared environment
- A lot of variance is not attributable to either genes or shared environment
. Most complex traits are shaped by many genes of small effect
DNA
Chromosomes are a packaging system for DNA, and form the essential unit in cell division. It is wound around spool-like histone proteins such that the total of about 2 metres of DNA in our cells can be packing into about 0.1 mm of chromatin
(Adenine-Thymine and Guanine-Cytosine)
DNA replication
To replicate, the strands unwind; each nucleotide attracts its complementary base (floating about in the cell nucleus), making two DNA molecules identical to the original
Replication errors affecting particular genes are called mutations
gene expression
just having a gene doesn’t do a whole lot. It’s only when the gene expresses itself (by triggering protein synthesis) that it has an effect. Gene expression depends heavily on the organisms internal and external environment
Polygenicity
involvement of multiple genes in 1 trait e.g. ADHD – 33 genes
Pleiotropy
involvement of one gene in multiple traits e.g. phenylketonuria
epigentetic mechanism
RNA methylation
DNA methylation
Histone acetylation
passive gene-environment interactions
- Parents create environment to suit their genetic predispositions
- This can enhance children’s inherited characteristics
evocative gene-environment interactions
- People have inherited tendencies to evoke certain responses
- These evoked responses reinforce inherited characteristics
active gene-environment interactions
- People select/create environments compatible with their inherited characteristics
- The resulting experiences enhance the effects of inheritance
dutch hunger winter
long term effects on dutch population
starvation had long lasting effects on the body, even after food was normal
Barker proposed that a situation where there is an adverse fetal environment (e.g, shortage of food), followed by a plentiful food environment may be a recipe for adult chronic disease.
The Dutch Famine Birth Cohort Study
revealed that the children of women who had starved during the Hunger Winter had health problems: including higher rates of diabetes, obesity, and cardiovascular disease.
late gestation period
- Glucose intolerance - Glucose intolerance is an umbrella term for metabolic conditions which result in higher than normal blood glucose levels - hyperglycemia. Associated with T2 diabetes
mid gestation period
- Glucose intolerance
- Microalbuminuria - Microalbuminuria means that there’s more of a protein called albumin leaking from your kidneys into your urine than normal. Associated with high blood pressure and diabetes
- Obstructive airway disease
early gestation period
- Glucose intolerance
- Hyperlipidaemia – hyperlipidaemia means your blood has too many lipids (or fats), such as cholesterol and triglycerides. One type of hyperlipidaemia , hypercholesterolemia, means there’s too much LDL (bad) cholesterol in your blood.
birth weights
Intrauterine exposures that have long-lasting consequences for adult health do not necessarily result in altered birth weight. Women exposed to the famine during mid- to late gestation had babies with significantly reduced birth weights. Babies whose mothers were exposed only during early gestation had normal birth weights; however, they grew up to have higher rates of obesity than those born before and after the war and higher rates than those exposed during mid- to late gestation
animal models
One mice is methylated, one is not. So, these mice are also genetically identical – they have exactly the same DNA. The reason they look different is due to epigenetic modifications, in this example DNA methylation. So when a certain gene is methylated, expression is reduced, then mice appear normal.
However, when expression of this gene is not methylated, it is over expressed leading to the obese, pale mouse with reduce lifespan and increased susceptibility to cancer.
diet in animal models
differences in maternal diet can alter gene expression in offspring. So, healthy behaviour including diet, and physical activity has links with adaptive epigenetic modifications.
What is also important to note, is the pale mice tend to have pale offspring, and the brown mice tend to have brown, skinny offspring. This is another example of transgenerational inheritance.
