Evolution + Genetics Flashcards
What is heritability, what does it measure and what is its importance in understanding human behaviour?
- How much of the differences between people can be explained by their DNA
- It is a measure of how well differences in people’s genes account for differences in their traits
- Important in giving a starting point for the influences of nature + nurture on complex traits
What is Darwin’s theory of evolution?
- Darwin argued evolution occurs through natural selection + that the adaptive, heritable traits associated with high rates of survival + reproduction, were more likely to be passed on to future generations
What is a theory?
- Should be comprehensive in explaining phenomena
- Should persist over time + between cultures in explaining phenomena
- Should be able to predict future events (or behaviour)
Explain Darwin’s theory of evolution by natural selection
Natural + sexual selection:
- “Survival of the fittest” - fitness refers to the ability to survive + reproduce
e.g. Darwin’s finches, “fitness” refers to the usefulness of the beak in obtaining food in their specific environment
Sexual selection: some members of a species having an advantage over others in terms of mating
What are the key principles of evolution by natural selection?
- Traits are heritable: can be passed down from one generation to the next
- Traits are variable: there must be a difference between individuals that usually follow a normal distribution and some people will be high in some traits + some will be low
- Some traits are more adaptive than others: they will be more likely to manifest at the population level (these manifest on average)
- These principles cause evolution in populations
Why is evolution important for psychology?
Evolution selects for behavioural as well as physical traits:
- Aggression
- Cooperation
- Mating strategies
What is an example of selection?
Domestication of dogs:
- Humans selectively bred dogs for some physical characteristics but also psychological traits
- Some dogs are more aggressive as they have been bred to hunt or guard
- Some are more intelligent as they have been selected for specific tasks
What are punnet squares?
- A punnet square is used to represent all the possible combinations of genes that could be inherited by the offspring of two parents
Dominant (B) purple
Recessive (b) white - The white flower’s gene is only expressed when an offspring inherits a recessive gene from each parent
- Punnett square shows the chance of a parent passing on each allele to express either a purple flower (BB, Bb) or a white flower (bb)
- White flower only occurs when both parents pass on the autosome for the recessive white gene
What are alleles?
At a given position on a homologous chromosome, there may be alternate forms of a gene called alleles
- There can be dominant + 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
- Genes are responsible for the type of body they express (e.g. eye colour)
- Alleles dictate what characteristic of the body part is expressed (e.g. brown, blue, green, grey etc.)
What are chromosomes?
- Chromosomes are a packaging system for DNA + form the essential unit in cell division
- Packaging is important as they DNA molecule is very long but needs to be made to fit inside the nucleus
- DNA is wound around histone proteins forming chromatin
What is a gene?
- Genes are functional sections of DNA at particular sites on chromosomes
- They are responsible for the type of body they express (e.g. eye colour)
- The info a gene carries is in the order of base pairs (Adenine-Thymine and Guanine-Cytosine) found in that section of DNA)
What are the functions of a gene?
- When activated, a gene starts the process of synthesising a protein
- A protein that end up synthesised as a result of an activated gene may act in the body in some way (e.g. give cells structural strength, trigger chemical events, carry messages, identify intruders, regulate the action of other genes)
- Just having a gene doesn’t do a lot, its only when the gene is expressed itself that it has an effect
- Gene expression depends on the organisms internal + external environment
What is DNA + how is it constructed?
-DNA carries the genetic material of an organism
- It is a double-stranded molecule made up of A-T + C-G base pairs held by a sugar-phosphate backbone
Explain DNA replication?
- To replicate, the strands unwind; each nucleotide attracts its complementary base (floating in the cell nucleus), making two DNA molecules identical to the original
- Replication errors affecting particular genes are called mutations - this is how variability occurs
What are Turkenheimer’s Laws of Behavioural genetics?
Turkenheimer (2000), Chabris et al., (2015)
1) All human behavioural traits are heritable
- Similarity: Identical twins reared apart > non-identical twins reared apart > than non-relatives reared apart
2) The effect of being raised in the same family is smaller than the effect of genes
- By adulthood, identical twins are no more similar whether raised apart or together
3) A substantial portion of variance is not attributable to either genes or shared family environment
- Identical twins reared together are not identical (e.g. different peer groups)
4) Most complex traits are shaped by many genes of small effect
- Hundreds or thousands of genes may be responsible for differences, even small ones
Describe Seymore Kety’s adoption studies research
- Looked at the biological + environmental influences on schizophrenia
- Environmental -> the environment the child was adopted into
- Biological -> the biological relationship that the child had with schizophrenia
Findings:
- When there is no evidence of biological schizophrenia + no evidence of schizophrenia in the family they were adopted into = 1% which is the concordance rate in the general pop
- When there was no biological relationship but there was an environmental relationship = 3% -> so there is an environmental effect for schizophrenia
- If the biological parents have schizophrenia but the adopted parents don’t = 9% -> 9x higher chance of developing schizophrenia than is observed in the general pop
- If there’s a biological relationship + environmental relationship = 17%
Describe Fischer’s identical twin studies
- Monozygotic - 50%
- Dizygotic - 10-19%
- Heritability - 80%
Limitations:
- Prenatal exposure
- Early life exposure
- Similar adoption environments
What problems do polygenicity + pleiotropy create in our efforts to understand behaviour?
Polygenicity- involvement of multiple genes in one trait
e.g. ADHD: 93 polymorphisms of 33 genes implicated
- Gene DRD4 shows strongest association, but accounts for only 25% of observed hyperactivity
Pleiotropy- involvement of one gene in multiple traits
e.g phenylketonuria (mutation of PAH gene), leads to learning difficulties, loss of hair + skin and eczema
How can the environment affect measures of heritability?
Lewontin’s plants:
- If you took seeds that were genetically identical (heritability = 100%) + placed them in highly controlled environments, controlling everything apart from nutrient solution (one condition has normal soil, one is deficient in nutrients), there would still be differences within the groups
What is epigenetics?
“the study of changes in gene function that are mitotically and/or meiotically heritable and that do not entail a change in the sequence of DNA” (Wu & Morris, 2001)
- Only about 2% of our DNA looks to be involved in protein synthesis
- The rest may be regulating DNA
What is regulating DNA + what do we think it does?
- Regulating DNA control the strength of gene expression
- One method is that some regulatory DNA inhibit protein-coding DNA until a regulation factor appears + disables this inhibition
- Regulation factors may be from outside the cell (chemicals, hormones) or events ocurring within the cell, including activities of other parts of DNA
What are the types of epigenetic mechanisms?
- Histone remodelling involves modifications to a histone protein (around which DNA is coiled) - can either decrease or increase gene expression
- DNA methylation involves the attachment of a methyl group to DNA - tends to reduce the expression of adjacent genes
- RNA methylation
- DNA methylation
- Histone acetylation
Give + identify examples of passive, evocative and active gene-environment interactions
Passive:
- Parents create environment to suit their genetic predispositions
- This can enhance children’s inherited characteristics
- Passive is one selected by your parents (e.g. middle class, well-educated, emotionally stable households)
Evocative:
- People have inherited tendencies to evoke certain responses
- These evoked responses reinforce inherited characteristics
e.g. aggression
Active:
- People select/create environments compatible with their inherited characteristics
- The resulting experiences enhance the effects of inheritance
- self-selected e.g. if you are introverted, you will select activities you can do by yourself
How did maternal deprivation during the Dutch Hunger Winter affect children according to gestation period?
- Supply issues towards the end of the second world war led to a famine in Holland that affected around 4.5m people + caused the death of 22,000 people
- Unexposed (born before) -> pregnant women whose foetuses were exposed to the dutch famine
- They were mostly exposed during the late trimester, the mid trimester, or the early trimester + then they were born
- Found that when the children grew up, they had a number of psychological disorders -> all trimesters were affected by glucose intolerance
- Exposure to a famine during a first trimester + parent and child were malnourished, the child has many physical + psychological issues e.g. stress, coronary heart disease, breast cancer
- So, the first trimester is the most critical + can effect children even when they grow up!!!!
What is transgenerational inheritance?
- When the mother was malnourished in early gestation (deprived during the 1st trimester, normal for the 2nd + 3rd) -> child had normal birth weight but when that child grew up + had a child of their own, their child had an increased birth weight
- Mothers malnourished in late gestation -> child had decreased birth weight + their own child had a normal birth weight
- We see the issues of the birth weights of these children as a consequence of things that happen to their grandparents
How has the evidence of transgenerational inheritance been validated using animal models?
- Two mice that are genetically identical (have exactly the same DNA)
- The reason they look different is due to epigenetic modifications e.g. DNA methylation
- When a certain gene is methylated, expression is reduced, then the mice appear normal
- When expression of a gene is not methylated, it is over expressed leading to the obese mouse with a reduced lifespan + increased susceptibility to cancer
- Diet can alter expression -> differences in maternal diet can alter gene expression in offspring, so healthy behaviour including diet + physical activity has links with adaptive genetic modifications
- Pale mice tend to have pale offspring + brown mice tend to have brown, skinny offspring (e.g. of transgenerational inheritance)
Psychological -> classical conditioning, took a mouse + stressed the mouse out + presented them with cherry blossom - Eventually you get the stressed mouse when presented with the cherry blossom
- When the mouse has offspring + introduce the smell of cherry blossom, the mice become stressed
