Behavioural Genetics Flashcards
What are the four types of nucleotides (bases) that make up a DNA polymer?
Thymine(T), Adenine(A), Guanine(G), and Cytosine(C)
Describe a DNA molecule
Two strands of nucleotides running in opposite directions, coiled into a double-helix.
Nucleotides from each strand are held together by hydrogen bonds
What are the specific pairs that nucleotides can form bonds in?
T - A or A - T
C - G or G - C
What is being referred to by ‘the sequence’
The order nucleotides are found along the strand
- very important for DNA coding
How many chromosomes do humans have?
23 pairs
46 in total
How do mutations in DNA occur?
A cell divides, the DNA helix is ‘unzipped’ so a complimentary strand can be made.
Sometimes errors are made when the new strand is made, so it isn’t identical.
If a repair enzyme does not fix this error, a mutation occurs
Name the three ways DNA mutations can occur
- Base-pair substitution
- one nucleotide and its partner are replaced by a different pair - Deletion
- the loss of one or more base pairs - Insertion
- the addition of one or more extra base pairs
What is RNA?
Ribonucleic acid
- single strand chemical that can serve as a template for the synthesis of proteins
What is the name of the process that creates RNA from DNA?
Transcription
What are the nucleotides found in RNA?
Uracil (replaces thymine)
Adenine
Guanine
Cytosine
What is mRNA?
Messenger ribonucleic acid
- is essentially a disposable copy of a gene
- carries the protein building information (codons)
What does mRNA do?
Translation
- carries protein-building message that is encoded by sets of genetic words which occur one after another along the length of DNA
- decodes protein-building information
- results in a polypeptide chain
What is a codon?
The protein building information carried by mRNA
- they are 3 bases long (e.g. A-C-G)
- there are 64 codons
- each codon refers to a specific amino acid
How many base pairs (nucleotide pairs) are there in a human chromosome?
50,000,000 - 300,000,000
What is a gene?
A segment of a chromosome
What is a homozygous gene?
An identical pair of alleles on the two chromosome
a base pair that is made up of the same base twice e.g. TT
What is a heterozygous gene?
A pair of alleles on the two chromosomes that are different (a base pair made up of two different nucleotides e.g. TA)
What is epigenetics the study of?
How your behaviour and environment can cause changes that affect the way your genes work
- e.g. some genes are only active at a certain point in one’s life
- changes are reversible and do not alter DNA sequence
What is a dominant gene?
A variant of a gene that expresses itself more strongly than any other version of the gene which the person is carrying
Shows a strong effect in both the homozygous and heterozygous condition
What is a recessive gene?
A gene who’s effects are hidden in the presence of a dominant gene
It will only show its effect in the homozygous condition (if there are two bases the same)
What is PER?
A protein produced by period genes, that promotes inactivity and sleep
What is TIM?
A protein produced by timeless genes, that promotes inactivity and sleep
What happens to the concentrations of PER and TIM throughout the day?
They oscillate
- synthesis of PER and TIM are very low at sunrise but increase throughout the day
- levels of the proteins themselves then increases later in the day, so PER&TIM levels are high at night
What is Familial advanced sleep disorder (ASPD)?
A Circadian Rhythm Sleep Disorder
A mutation in the Per2 gene, that causes persistent advanced onset of sleep and awakening
- sufferers typically experience sleepiness in the early evenings rather than later on (at night)
What is a proband?
A person serving as the starting point for a genetic study of a family
How was Familial advanced sleep disorder (ASPD) discovered?
- Proband’s sleep phase was brought forward 4-8 hours
- Proband participated in time-isolation experiment for 3 weeks (stayed in an environment with no time cues)
- showed a 1 hour shortening in her circadian period
- a mutation in the Per2 gene was identified
What are Familial natural short sleepers (FNSS)?
Circadian Rhythm Sleep Disorder
- People with mutation in the DEC2 gene
- Carriers needed only 6 hours of sleep a day
- mutation leads to difference in EEG architecture of sleep (higher delta power during slow-wave NREM & less REM sleep)
What is Brain-Derived Neurotrophic Factor (BDNF)?
A neurotrophin, important in neurogenesis and plasticity
What is Heritability?
Refers to how much characteristics depend on genetic differences
What can change the impact of genetic influences (heritable genes)?
Strong environmental influences can cause genetic influences to have less of an impact
How do genes affect our behaviour?
- They do not directly produce behaviours
- Genes produce proteins that increase the probability that a behaviour will develop under certain circumstances
- Genes can also have an indirect effect - can alter your environment by producing behaviours or traits that alter how people in your environment react to you
What is the most common twin-model used in twin research to explain the amount of variance between twin pairs?
The ACE model:
- A (or h2) = Additive genetic effect. This is the proportion of variance of a phenotype explained by genetic influences
- C = Common environmental influences (proportion of the variance of a phenotype explained by shared environment)
- E = Non-shared environmental influences, unique to each twin (proportion of the variance of a phenotype explained by a non-shared environment)
What are some examples of Non-Shared Environmental factors for children growing up in the same family?
Peers
Child-specific illnesses / events
Events occurring to an individual
What are some examples of Shared Environmental factors for children growing up in the same family?
Socioeconomic status
Characteristics of the home e.g. number of books in home
Parenting less likely to be shared - can’t be treated in exactly same way
What is the Univariate twin model?
Asks how much of the variance (between twins) in a trait is explained by A, C or E from the ACE model?
What is the Bivariate twin model?
Asks to what extent is trait 1 caused by the same genetic and environmental influences as trait 2
What is Genetic Correlation?
Is independent of the phenotypic relationship between two traits
Is independent of the heritability estimates of either trait
What are the Pros of twin studies?
- All Ps are same age
- Can partition variance into A + C + E
- Reasonably representative of general population
- Don’t need a control group
What are the Cons of twin studies?
- Requires large samples (>1000 pairs) to have sufficient power
- Design has many assumptions
- Some twin-specific characteristics are not generalisable to singletons
What are the assumptions of twin studies?
- Findings from twins are generalisable to singletons
- Assumes no gene-environment correlation or interaction
- Equal environments assumption: assumes environmental influences are equivalent for MZ and DZ pairs
