Evolution

Question 1

Evolution and natural selection

Answer 1

• The environment cannot support an unlimited population growth.
  
  • Finite amount of resources in the world
  • Organisms are in constant competition not just for food but other resources too.
  • Organisms vary in traits
    ○ Some traits will be advantageous and others are unhelpful.
  • In this example green beetles tend to get eaten by birds (they can spot them easily)
    ○ The surviving brown beetles will have brown baby beetles because this trait has a genetic basis
    Brown colour becomes more common in population and eventually all beetles will become brown

Question 2

principle of natural design for gene replication

Answer 2

we are a constellation of genes that drive physiological processes and behaviours. Evolution does not operate in individuals, rather evolution operates in genes. Genes need to make it to the next generation- idea that advantageous traits are more likely to be passed onto the next generation

Question 3

superabundance

Answer 3

animals and plants produce more offspring than necessary- some of the offspring will survive and pass on their genes to the next generation

Question 4

natural variation

Answer 4

each offspring is somehow different.
no identical offspring- need that variation to survive and pass on advantageous traits and genes

Question 5

selection pressures

Answer 5

○ Imposed pressure- when we artificially impose advantageous traits onto offspring e.g. breeding show dogs
○ a) Natural selection pressures: Organisms must ensure that the genes survive so they can make it to the next generation
○ Selection pressure: predation, susceptibility to disease and toxins, dangerous environment
How do organism respond to those pressures? They are called adaptations- Usually adaptations have a trade off price to pay…. The smaller the trade off the better the adaptation

Question 6

human evolution

Answer 6

• How was the environment when we evolved?: this is called the Environment of evolutionary adaptiveness (EEA): this is something that we figure out from selection pressures at the time
  
  • Behaviours or traits that occur universally in all cultures are good candidates for evolutionary adaptations:
  • Ability to infer others’ emotions- useful for deciding between threats
  • Discern kin from non-kin- know not to mate within family breeding lines as it produces mutations
  • Identify and prefer healthier mates- identify people to reproduce with to pass on healthy genes
    Cooperate with others

Question 7

evolution of the brain

Answer 7

• Smaller animals have a smoother brain
  Size and complexity of the brain shows that we are more intelligent- complexity of us as a species

Question 8

why can humans compete with other species?

Answer 8

• Agile hands: tools- we can build, make fire etc
  
  • Colour vision: opportunities and dangers
  • Mastery of fire
  • Bipedalism: Walk long distances, Carry tools and food
  • Linguistic abilities: pass information, make plans, form complex civilisations

Question 9

mendelian genetics

Answer 9

• Darwin (1809-1882) created the theory of evolution however two facts were not understood at the time:
  
  • 1- Why members of the same species differ from one another, we are actually all different
  • 2- How anatomical, physiological and behavioural traits are passed from parents to offspring.
  • Mendel (1822-1884) studied inheritance in pea plants.
  • He studied dichotomous traits, and he began his experiments by crossing the offspring of true breeding lines. First, must define these concepts…
  • True breeding lines are breeding lines in which interbred members always produce offspring with the same trait, generation after generation. In the pea case it would be green seed or yellow seeds.
    Mendel crossed two different true breeding lines and then their offspring. One trait, dominant trait, appeared in all of the first generation offspring, the other trait, which he called the recessive trait, appeared in about one quarter of the second generation offspring.

Question 10

Mendel’s results and theory

Answer 10

Idea 1: There are two kinds of inherited factors for each dichotomous trait – today the inherited factor is called gene.
- Idea 2: Each organism possesses two genes for each of its dichotomous traits. In the case of widow’s peak the genes would be W and w
- The two genes that control the same traits are called alleles
- Two genes that control the same trait are called alleles (in case of pea colour would be Yellow and Green, in case of widow’s peak would be W and w).
- Organisms that possess two identical genes for a trait that are said to be homozygous (WW) and those possess two different genes for a trait are said to be heterozygous for that trait.
- Idea 3: One of the two genes for each dichotomous trait dominates the other in heterozygous organisms- if you inherit an uppercase W you will have a widows peak
- Idea 4: Dichotomous trait, each organism randomly inherits one of its father’s two factors and one of its mother’s two factors.
- Idea 4: Dichotomous trait, each organism randomly inherits one of its father’s two factors and one of its mother’s two factors.
- We do not know if Lily is heterozygous or homozygous, but she definitely carries at least one dominant allele- therefore we look at the offspring. We know that Herman carries two recessive genes as he has a straight hairline

Question 11

genotype vs phenotype

Answer 11

• a genotype is the combination of alleles an organism inherits from its parents (genes)
• phenotype is the organisms appearance

Question 12

chromosomes

Answer 12

• Not until the early 20th century – genes were found to be located on chromosomes.
  
  • Chromosomes occur in matched pairs (with ONE exception- sex chromosomes), and each species has a characteristic number of pairs in each of its body cells.
  • Human have 23 pairs- one chromosome from each parent
    The two genes that control each trait are situated at the same location (loci), one on each chromosome of a particular pair.

Question 13

sex chromosomes and sex linked traits

Answer 13

• There is one exception to the rule that chromosomes always come in matched pairs.
• Traits that are influenced by genes on these chromosomes are referred to as sex linked.
• Traits that are controlled by genes on the sex chromosomes occur more frequently in one sex than the other.
• If the trait is dominant it will occur in females because females have twice the chance of receiving the X chromosome.
• Recessive sex linked diseases occur more frequently in males (Haemophilia, colour blindness).

Question 14

division of chromosomes

Answer 14

• The process of cell division that produces gametes is called meiosis.
• Chromosomes divide, and one chromosome of each pair goes to each of the two gametes that result from the cell division.
  Sperm + egg = zygote.
• As a result genetic recombination, each of the gametes that formed the zygote that developed into you contained chromosomes that were unique.
• In contrast to the meiotic creation of the gametes, all the cell division in the body occurs by mitosis.

Question 15

chromosome structure and replication

Answer 15

• Each chromosome is a double stranded molecule of deoxyrybonucleic acid (DNA).
• Each strand is a sequence of nucleotide bases attached to a chain of phosphate and deoxyribose.
• There are four bases.
• The two strands that compose each chromosome are coiled around each other and bonded together by the attraction of adenine for thymine and guanine for cytosine.
• Guanine and cytosine are paired and adenine and thymine are paired
• Two strands that compose chromosomes are bonded together by the attraction between the bases
• • Replication if a critical process of the DNA molecule. Without it, mitotic cell division would not be possible.
• The process needs to be accurate. Sometimes mistakes happen, they are a called mutations.
• In most cases, mutations disappear from the gene pool within a few generations because the organisms that inherit them are less fit.
  In rare instances, mutations increase fitness and in so doing contribute to rapid evolution.

Question 16

mutations

Answer 16

• Mutations can be divided into two types:
• 1- Chromosome mutations: Change in chromosome number or chromosome structure : Down’s syndrome.
• 2- : Single-gene mutations: change in DNA structure within a particular gene: sickle cell disease.

Question 17

the genetic code and gene expression

Answer 17

• Mechanism of gene expression:
• 1- Strand of DNA unravels
• 2- Transcription: Messenger RNA (mRNA) synthesised from DNA
• 3- mRNA leaves nucleus and attaches to ribosome in the cell’s cytoplasm
• 4- Translation: Ribosome synthesises protein according to 3-base sequences (codons)

Question 18

enhancers

Answer 18

• Structural genes comprise only a SMALL portion of the chromosome.
  
  • Enhancers are stretches of DNA whose function is to determine whether particular structural genes initiate the synthesis of proteins and at what rate.
  • This determines how a cell will develop and how it will function once it reaches maturity.
  • Proteins that bind to DNA and influence the extent to which genes are expressed are called transcription factors.
    Transcription factors control the enhancers. Transcription factors are influenced by signals received by the cell from its environment.

Question 19

human genome project

Answer 19

• One of the most ambitious scientific projects of all times, it began in 1990.
• Its purpose was to compile a map of the sequence of all 3 billion bases in the human chromosomes.
• It was assumed that once the human genome was described it would be relatively straightforward to link variations in the genome to particular diseases and then develop treatments.
• The three major contributions of the project were:
  
  • Development of new techniques to study DNA.
  • The discovery that humans have a relatively small number of genes (20,000).
  • Only about 2% of chromosome segments contain protein-coding genes.
    This discovery led to the rapid growth of a new field of research: epigenetics

Question 20

modern genetics: the growth of epigenetics

Answer 20

• Epigenetics focuses on mechanisms that influence the expression of genes without changing the genes themselves.
• It refers to modifications of DNA and DNA packaging that alter the accessibility of DNA and potentially regulate gene expression WITHOUT changing the sequence of DNA itself.
• Assumed to be the means by which a small number of genes are able to orchestrate the development of humans in all their complexity.
• It is focuses on the role of experiences in genetic expression.
• Many epigenetics mechanisms have been discovered, two of the most widely studied are DNA methylation and histone remodelling.

Question 21

epigenetic mechanisms: DNA methylation

Answer 21

• DNAm is most commonly studied in human populations for two major reasons:
• 1- It is easily quantifiable, and relatively stable.
• 2- Does not require complex processing of samples after collection.
• One of the main roles of DNAm is in cellular differentiation. As stem cells divide and gradually differentiate into specific cell types, DNAm patterns become increasingly cell type specific.
• This explains how cells with the same genetic sequence, such as neurons and white blood cells, have very different functions.
• Thus in contrast to genetic information, DNAm is highly tissue specific.

Question 22

epigenetic mechanisms

Answer 22

• These mechanism allows for the cell-to-cell transmission of epigenetic patterns associated with the cell’s past exposures —they create a form of cellular memory that can be passed along to daughter cells.
  It is these patterns that can be detected in studies examining associations between current DNAm and exposures or events in the past.

Question 23

epigenetic and inheritance

Answer 23

• We used to think that a new embryo’s epigenome was completely erased and rebuilt from scratch.
• Reprogramming is important because eggs and sperm develop from specialised cells with stable gene expression profiles.
• In other words, their genetic information is marked with epigenetic tags. Before the new organism can grow into a healthy embryo, the epigenetic tags must be erased.
• So basically the belief was that a new embryo’s epigenome had to be completely erased and rebuilt from scratch.
• This needs to be done in order for an embryo to make every type of cell in the body.
• However this is not entirely true. Some epigenetic tags remain in place as genetic information passes from generation to generation, a process called epigenetic inheritance.
• Epigenetic inheritance is an unconventional finding. It goes against the idea that inheritance happens only through the DNA code that passes from parent to offspring.
• It means that a parent’s experiences, in the form of epigenetic tags, can be passed down to future generations.
  In mammals, about 1% of genes escape epigenetic reprogramming through a process called imprinting.

Question 24

transgenerational epigenetics

Answer 24

• These mechanisms can be induced by particular experiences such as neural activity, hormonal state, changes to the environment.
• These changes can last a lifetime.
• The interesting question is: Can those experience-induced changes be passed to your offspring?
• Yes, it was first observed in plants but now also evidenced in mammals: Mice trained to associate electric shock to odour. This effect is passed to offspring.
• Making a case for epigenetic inheritance in humans remains especially challenging because:
  
  • Humans have long life spans, making it time consuming to track multiple generations.
  • Humans have greater genetic diversity than laboratory strains of animals, making it difficult to rule out genetic differences.
  • Ethical considerations limit the amount of experimental manipulation that can take place.

Question 25

twin studies of epigenetic effects

Answer 25

• Fraga et al 2005: tissue samples from 40 pairs of MZ twins, age range 3-74y:
• Screened tissues for DNA methylation and histone modifications.
• MZ twins were epigenetically indistinguishable in early life but differences accumulated as they aged.
• Lifestyle factors (external factors)
  Epigenetic drift due to cell division (internal factors)

Question 26

epigenetic of behavioural development: interaction of genetic factors and experience

Answer 26

• Selective breeding of ‘maze bright’ and ‘maze dull’ rats
• Early psychologists assumed that behaviour develops largely through learning.
• In 1934 Robert Tryon (Behavioural psychologist) trained a large heterogenous group of laboratory rats to run a complex maze. The rats received a food reward when they reached the goal box.
• Then mated the females and males that least frequently entered incorrect alleys during training : maze bright, and bred the females and males that most frequently entered incorrect alleys during training: maze dull.
• Then accessed the performance of offspring and kept mating brightest and dullest for 21 generations.
• By the eighth generation, there was almost no overlap in the maze learning performance of the two groups.
• The maze bright rats were superior maze learners not because they were more intelligent but because they were less fearful – a trait that is not adaptive in many natural environments.
  Selective breeding studies have proved that selective breeding based on one behavioural trait usually brings a host of other behavioural traits with it.

Question 27

How would you assess the relative contributions of genes and experience in the development of individual differences in psychological attributes?

Answer 27

• Study individuals of known genetic similarity
• Adoption studies: the most extensive study is the Minnesota Study of Twins Reared Apart – Bouchard et al (1990)
• • 59 pairs on monozygotic and 47 pairs of dizygotic twins who had been reared apart and as many pairs that had not.
• • Age range: 18-69 years.
• • Each twin was brought to University of Minnesota for approximately 50 hours of testing: intelligence and personality.
• Would the adult monozygotic twins reared apart be similar or different?
• The study was remarkably consistent, both internally and externally.
• In general adult monozygotic twins were more similar to one another on ALL dimensions than dizygotic twins regardless how they were reared.
• This takes us to the contribution of genetic variation to this study.
  Heritability estimate: numerical estimate of the proportion of variability that occurred in a particular trait in a particular study as a result of genetic variation.

Question 28

heritability estimate

Answer 28

• Heritability estimate: Numerical estimate of the proportion of variability that occurred in a particular trait in a particular study as a result of genetic variation.
  
  • Numerical estimate (between 0-1). Sometimes represented as percentages (100% would be 1).
  • Basically you MUST have VARIATION in a trait to be able to get a value above 0
  • This means that:
    ○ A) It cannot be studied in one individual
    ○ B) The trait that you are exploring has to show variability in the population
  • The estimate depends upon which population you examine.
  • Numerical estimate of the proportion of variability that occurred in a particular trait in a particular study as a result of genetic variation.
  • For example, the heritability of hair colour in a Chinese population would be quite low, and here quite high.
    This is because in China there is little “natural” variation in hair colour – variation that is genetically caused. As such, any large variations are usually due to environmental factors, such as artificial dyes.

Question 29

genetics of human psychological differences: intelligence

Answer 29

• Twin studies on the effect of experience on heritability
• Turkheimer et al 2003: heritability of intelligence in upper-middle class 75%
• Heritability intelligence in 7y old twins: families from low SE status: 10% and high SE status 70%
• This effect was replicated and extended to other age groups
• Implications: intelligence develops from the interaction of genes and experience, one can inherit the potential to be of superior intelligence, but this potential is rarely realised in a disadvantaged environment
• This has implications for the programs to help to develop individuals in low SE status.

Question 30

three ‘laws of the genetics of complex traits (Plomin & Deary, 2015)

Answer 30

All traits show genetic influence.
Height, BMI, aggression, extraversion, intelligence.
No traits are 100% heritable.
Nothing has a heritability factor of 1
Role of environment.
Heritability is caused by many genes of small effect.
No single “intelligence gene”.

Question 31

family studies

Answer 31

• Genetic similarity between parents and offspring, and siblings and siblings is 50%.
  
  • 25% for grandparent and child.
• Do we see increases in similarity between relatives with greater genetic similarity?
• Example – increasing risk of schizophrenia when first vs second-degree relatives have schizophrenia (Chou et al, 2017).
  
  • Dose-response relationship between schizophrenia and genetic distance.
  • First-degree relative: 6.4 x higher than population; 2.4 x for second degree relative.
• Compared to twin studies,
  easier to find a sufficient
  sample size
• All relatives must have the same relationship.
  Risk of confounding of genetic and environmental effects because the formula ignores non-additive genetic effects and shared environmental factors.
  Underlying assumptions about genetic relationships are often flawed due to long segments of DNA
  being inherited.

Question 32

twin studies

Answer 32

• Non-identical, dizygotic, DZ twins
• 50% genetic similarity, like siblings.
• Developed from fertilisation of two eggs and two sperm.
• Identical, monozygotic, MZ twins.
• Genetically identical at birth.
• Developed from a single egg and sperm that split.
• Concordance rate: Percentage of cases where both twins have a certain characteristic.
  If it’s higher in MZ twin than in DZ twins, we can infer that there is an influence of genetics on the characteristic.
  Conceptually simple
  Can be calculated without
  advanced statistical programs
  Does not require genotyping
  Assumes gene environment correlations and interaction are minimal .
  Assumes variance explained by shared environmental factors is identical in monozygotic and dizygotic pairs.
  Could result in over estimation of heritability.

Question 33

adoption studies

Answer 33

• People adopted out of biological family.
• Compare how similar they are to adoptive vs biological relatives.
• If more similar to adoptive relatives we can say there’s a stronger influence of environment.
  If more similar to biological relatives, we can say there’s a stronger influence of genetics.

Question 34

twins reared apart

Answer 34

• Twins adopted into different families.
  
  • Separation of genetics and environment.
• Ethics – obviously can’t do this research.
  
  • But natural experiments possible.
    Minnesota study of twins reared apart – Bouchard (1990).
    Considered the best estimate
    of heritability due to
    most number of underlying
    assumptions being true
    Difficult to find a sufficient sample size..
    Need to have twins that were separated early in life.
    Biological parents, adopted twins, and adoptive parents may have characteristics that cannot be generalizable to the average person.

Question 35

cohort studies

Answer 35

• Lothian Birth Cohort
• 1932- 1947 - every child in school in Scotland took part in an intelligence test, providing an IQ score them at age 11.
  
  • ~1500 members
• Starting from ~2000, University of Edinburgh has been following them up every 3 years to look at health and cognitive ageing. Also taken genetic samples.
• Dutch Famine Birth Cohort
• Dutch famine 1944-45 – food supplies to The Netherlands cut off by Nazi party.
  
  • ~20,000 deaths, 4.5 million affected.
• Important discoveries for genetics and epigenetics.
  Evidence of DNA methylation – epigenetic changes due to famine passed on to offspring- Cardiovascular disease, obesity.
  Genetic and environmental influences on health, learning, intelligence, cognitive development.

Question 36

what is intelligence?

Answer 36

• Our ability to learn, reason and solve problems (Plomin & von Strum, 2018).
• Latent trait, not directly observable (like e.g. height), but it’s something we can infer from tests.
• Generally assumed stable over time (Deary et al, 2013).
• Spearman (1904) two-factor theory of intelligence.
  
  • g “general intelligence” – general cognitive ability.
  • s “specific ability” – specific factors e.g. arithmetic, verbal ability etc.

Question 37

intelligence testing- Ravens progressive matrices

Answer 37

• Introduced in 1938.
• General intelligence and abstract reasoning.
• Identify missing item that completes a pattern.
• Language-independent.
  Narrow focus on intelligence.

Question 38

intelligence testing- Weschlers adult intelligence test

Answer 38

• Introduced in 1955.
• Most frequently used in clinical practice.
• 15 subsets yielding full IQ score.
• High reliability on the surface, but questionable for IQ scores <50 (Kaplan 1994).
  Debate over sensitivity to neural impairment?

Question 39

heritability and intelligence

Answer 39

• Heritability estimates for intelligence range from 0.4 – 0.6, around 0.5 on average (Plomin and Deary, 2015).
  
  • Some estimate put this as high as 0.8, but we’ll see why there’s a difference later in the lecture.
• Infancy: Heritability estimates are as low as 0.2
• Middle childhood: Heritability estimates are around 0.4
• Adulthood: Heritability estimates are as high as 0.8
  General intelligence is also one of the most heritable behavioural traits, with heritability increasing from 40% in childhood to 80% in adulthood

Question 40

education and intelligence

Answer 40

• Birch and Galloway (2011) – data before and after a reform in compulsory schooling in Norway showed increase in IQ scores between ages 7-9 and 19.
• Supported Ritchie and Tucker-Drob (2018) – meta-analysis.
  IQ scores increased as years of schooling increased

Question 41

nutrition and intelligence

Answer 41

• Northstone et al (2011) – nutrition is linked to IQ scores. Lower scores in children with diets high in fat, salt and sugar than those with “healthier” diets.
  
  • N = ~7000, ALSPAC – cohort study.
  • Adjusted for maternal education, social class, gender.
• Nutrition influences cognitive and neural development.
  
  • Nyaradi et al (2013).
    Nakamura et al (2024).

Question 42

socioeconomic status and intelligence

Answer 42

• Turkheimer et al (2003) - Heritability intelligence in 7y old twins: families from low SE status: 10% and high SE status 70%.
  
  • Similar results reported by Harden et al (2007).
• Why?
  Schooling, living situations, books/computer access, academic focus, cognitive development, stress….i

Question 43

interaction between genetics and SES

Answer 43

• Rask-Anderson et al (2021) – greater impact of genetics in deprived populations?
• Tucker-Drob et al (2010) – emergence of interaction by 2 years old.
  
  • Genes had a greater influence on intelligence for high-SES than low-SES families.
  • Important quote from Tucker-Drob - In more advantaged homes, children have the opportunity to evoke and select environmental experiences that allow them to maximize their genetic potential for cognitive development, whereas this process is stifled in disadvantaged homes
• Hanscombe et al (2012) – UK sample, TEDS participants.
  SES moderates the effect of the environment, not genetics.