Behavioural Genetics Flashcards
Who is known as the father of behavioural genetics?
Sir Francis Galton
Darwin’s 1st cousin
Who was responsible for a revival of the eugenics movement in the 1920’s?
Goddard, stated that intelligence and mental level were determined by chromosomes and environment has minimal impact
Who conducted the ‘hereditary health courts’? How many people were sterilised?
The Nazis. 400k with hereditary illness, 225k with physical or mental disabilities - eventually extended to Jews and ‘political undesirables’
What is the ‘tabula rasa’ and how did it effect studies of psychology?
Tabula Rasa means ‘blank slate’ and was a theory put forth by John Locke in 1690. It dominated psychology until the late 1960’s and was not challenged
How did John Money describe Gender Neutrality in 1955?
Sexual behaviour and orientation doesn’t have an innate, instinctive basis. Sexuality becomes masculine or feminine in the course of experiences growing up
What is behavioural genetics?
The study of the genetic and environmental bases of behaviour
Turkheimer, in 2000, came up with the 3 laws of behavioural genetics. What are they?
First law - all human behavioural traits are heritable
Second law - The effect of being raised in the same family is smaller than the effect of genes
Third law - A substantial portion of the varitation in complex human behavioural traits in not accounted for by the effects of genes or families
Who conducted the first behavioural genetics study? What was its title? When was it conducted?
- Sir Francis Galton
- Hereditary Genius
- 1869
What do we mean when we say familial?
Something that occurs more within a family than would occur in the general population as a whole e.g. depression, intelligence
What is heretability?
Proportion of total phenotypic variation explained by genetic variation, ranges from 0 to 1
How do we pull apart genetic and environmental effects?
Natural experiments e.g. family studies, twin studies and adoption studies. Twin studies are most helpful
Why are twin studies helpful in teasing apart genetic and environmental effects?
Allow comparisons in discrete traits and continuous traits between MZ and DZ twins due to shared environment
Explain identical twins
Also known on monozygotic twins - fertilisation of a single egg by single sperm - 100% shared genetic material
Explain non-identical twins
Also known as fraternal/dizygotic twins - fertilisation of two eggs by two sperm - share 50% genetic material
What is zigosity and what 3 factors is it determined by?
To determine whether twins are identical or non-identical is to determine zygosity. Determined by:
- Genotyping
- Questionnaires
- Expert judgement
Describe the Falconer (ACE) model
A - additive genetics
C - common environment
E - unique environment
When looking at heretability in twin studies, what are some consistent findings?
1) MZ twins are more similar than DZ twins
2) MZ twins are not absolutely identical
3) Psychological and physical disorders/traits exhibit similar heretability patterns and ACE estimates
What are mendelian genetics?
How genes were discovered/identified - particularly good for dichotomous traits (yes/no traits)
What is quantitative genetics?
The genetic study of trait inheritance showing a continuous distribution of phenotypes in a segregating population
According to the ACE model, what has been found about most traits?
Moderate to large heritability estimates (a2) are seen in most traits
Moderate unique environmental estimates (e2) are seen in most traits
Little to no common environment (c2) is seen in most traits
What is meant by the central dogma?
Basically what makes us, us. The process of DNA being transcribed to RNA to proteins to the body
What is DNA?
DeoxyriboNucleic Acid. The hereditary component present in all cells
What are the four bases that compose DNA?
Adenine complementary to Thymine
Guanine complementary to Cytosine
At cell division, what is the length of a human mitotic chromosome, and how much DNA does it contain?
5 microns in length, containing 5 cms of DNA
2 metres of DNA in each cell
How many pairs of chromosomes are contained in the human body?
22 autosomes (non-sexual chromosomes) 1 pair sex chromosomes
How is the vast length of DNA contained in the body?
chromosomes contain long DNA molecule, wrapped in proteins which creates chromatin
chromatin coiled, supercoiled to create chromatids
What is a gene?
- stretch of DNA ‘functional unit’
- the basic unit of heredity
- hundreds of genes per chromosome
How many genes does the human genome contain?
20 000
What is a genetic mutation?
A point or section of genetic code that varies between different people
What are Single Nucleotide Polymorphisms? (SNPs)
A single base-pair has been altered. A polymorphism is a genetic mutation prevalent in >1% of the population
What are the names of the enzymes that unzip DNA and rejoin DNA?
Helicase unwinds DNA
DNA Polymerase is building it again
Explain what is meant by DNA being ‘anti-parallel’
one strand runs 5’ to 3’ (leading)
the other 3’ to 5’ (lagging in replication)
What is messenger RNA? (mRNA)
mRNA delivers data from DNA to ribosome to enable protein synthesis
What does Thymine change to when DNA transcribes to RNA?
Uracil
How do so few genes create so much variation?
- Splicing
- Epigenetics - micro RNAs
- Epigenetics - DNA methylation
Explain splicing
Splicing means certain parts of the RNA are dropped
What are micro RNAs?
Small bits of RNA
Can regulate gene expression by interacting with mRNA
They cause gene silencing
What is the relevance of micro RNAs to brain disease?
they target multiple genes simultaneously, have already been found to be significant in Schizophrenia
What is DNA methylation?
Switches genes off essentially
Usually blocks promoter > no transcription factor can bind > gene switched off
What is a variant?
A genetic mutation that is prevalent in <1% of the population or unknown
Define linkage studies as a molecular genetic method
systematic approach using microsatellite markers across the genome in families to identify disease risk
Describe association studies as a molecular genetic method
using genetic markers at specific genes in unrelated people, testing for increased burden in the affected group
What is a whole-genome (WGA) study?
- access over 1m markers across the genome simultaneously on a “SNP array”
What is a copy number variant?
Chunks of a genome that may or may not be duplicated from person A to person B
What is missing heritability?
- the gap between twin estimates and molecular estimates
What are some factors that could contribute to missing heritability when it comes to study design?
1) Differences in phenotype between studies (clinical v population studies
2) Differences in phenotype within studies (e.g. different illnesses grouped together)
What is population stratification? How can it contribute to sample heterogeneity?
Population stratification is differing frequencies of markers sensitive to population difference - so it is going to affect the heterogeneity of the sample
What is the fourth law of behavioural genetics?
A typical human behavioural trait is associated with many genetic variants, each accounting for a very small percentage of behavioural variability
What does epistasis mean?
gene-gene interactions, could result in an inflation in twin heritability estimates
current available genetic data shows little support for epistatic effects
Give two noteworthy points about heritability:
1) heritability is population specific
2) as environmental effects go up, genetic effects go down
Has there been evidence of gene-environment interaction found?
No convincing evidence - it may exist but only observable in limited situations
Define epigenetics?
study of changes in gene expression caused by mechanisms other than changes in the underlying DNA sequence. Changes are called epigenetic variation
Who coined the epigenetic landscape?
Waddington, 1951
What is the musical score analogy for epigenetics?
The musical score is your DNA sequence, the annotations one makes on the sheet music is the epigenome (expression of the DNA sequence)
What is the process behind DNA methylation?
Cytosine molecule being paired with a methyl group, methylated
Is there evidence to support that epigenetics can have a psychological impact?
There is very strong evidence to suggest that epigenetic workings have an impact on psychological outcomes
Summarise the findings of the Weaver study with rats and licking
- Differences in DNA methylation patterns emerge in first week of life
- reversed with cross-fostering
- persist into adulthood
What are microRNA (miRNA) and when were they discovered?
Discovered in 1993, they are small non-coding RNAs (19-22 nucleotides) in length that post transcriptionally regulate gene silencing by inhibiting function of target mRNAs through complementary binding
More simply, they stop the mRNA from becoming a protein
How are miRNAs relevant to brain disease?
- majority expressed in the brain
- target multiple genes simultaneously
- impacted by trauma and other environmental stimuli
What is a phenotype?
set of observable characteristics resulting from one’s genotype-environment interaction
What is a genotype?
the genetic constitution of an individual organism
