Biology & Behaviour: Comprehensive Study Notes

Biology & Behaviour

Genetics Background

• Principles of heredity used for a long time (e.g., selective breeding)
• James Watson, Francis Crick, & Rosalind Franklin → structure of DNA in the 1950’s
• Mapped the entire genome: the complete set of DNA of any organism, including all its genes
• Gene synthesis: method for producing DNA
• Genes in humans
• Fewer than previous estimates [Willyard, 2018]
• Genes themselves make up a small part of the genome
• 1\%

Models of Hereditary & Environmental Influences

• 3 key elements:
  • Genotype: the genetic material an individual inherits
  • Phenotype: the observable expression of the genotype, including both body characteristics and behaviour
  • Environment: every aspect of individuals and their surroundings other than genes
  • Genotype → Phenotype → Environment (and interactions among them)

Relationships

• 5 relationships:
  1. Parent’s genotype → Child’s genotype
  2. Genotype → Phenotype
  3. Environment → Phenotype
  4. Phenotype → Environment
  5. Environment → Genotype
• Diagrammatic sense: Genotype ↔ Phenotype ↔ Environment, with directional arrows as listed

1. Parent’s Genotype → Child’s Genotype

• Gametes → zygote
• Nucleus of every cell = chromosomes made up of two DNA strands
• “Biochemical instructions” found in genes: sections of chromosomes that are the basic unit of heredity in all living things
• Segments of DNA that code for the production of proteins
• Guarantee similarities AND guarantee differences
• 2 main mechanisms that promote variability (aka individual differences):
  • Random assortment (crossing-over)
  • Mutation: change in DNA (spontaneous errors or environmental factors)
• Can be harmful or beneficial (basis of evolution)

Mechanisms for Variability

• 2 main mechanisms that promote variability (aka individual differences):
  • Random assortment (crossing-over)
  • Mutation: change in DNA through spontaneous errors or environmental factors
• Can be harmful or beneficial
• Basis of evolution

Sex Chromosomes

• Sex chromosomes: the chromosomes (X and Y) that determine an individual’s designated sex at birth
• Genetic females = XX; All female eggs
• Genetic males = XY; Sperm are half male, half female
• Responsible for sex determination

2. Child’s Genotype → Child’s Phenotype

• Every cell contains every gene, but never use them all
• Genes can influence behaviour IF: they are switched on in the right place, at the right time, and for the right length of time
• How do we ensure these conditions are met?
  • Regulatory genes: genes that control the activity of other genes
  • Chain reaction of genetic events
  • Environment – presence or absence of an environmental trigger

Dominance patterns & Alleles

• Dominance patterns: partial gene expression is also possible
• 1/3 of human genes have two or more different forms, or alleles
• Influence the same trait, but give different outcomes
• Dominant-recessive pattern
• Sex chromosomes work differently
• Genetic males are more likely than females to suffer from sex-linked inherited disorders
• Polygenic inheritance: inheritance pattern in which traits are governed by more than one gene

Genes x Environment

• Genes and environment are continually interacting
• Can lead to different expressions of the genes in different environments
• Example: PKU (phenylketonuria)
• Impact can be avoided by altering environment
• Gene-environment correlations from parents
  • Parent’s genes → parent’s preferences/abilities → environment provided to child
• Study: effects of parental genes on children’s educational outcomes [Kong et al., 2018]
• Genetic nurture

4. Child’s Phenotype → Child’s Environment

• Each child will evoke responses from others
  • Outgoing baby vs. shy baby
• Active selection: Infants → what objects to pick up; Childhood → playmates, activities, etc.
• Ability to shape their own environments
• Impact on intellectual development

5 Child’s Environment → Child’s Genotype

• Genetic structure is ‘stable’ but, genetic expression can be altered
• Genetic encoding of proteins → alters gene expression (phenotype)
• Chain reaction of genes turning on/off other genes
• Epigenetics: the study of stable changes in gene expression that are mediated by the environment
• Epigenetic mechanisms can alter gene function
• Can be passed down to future generations

Epigenetics: Methylation Example & Evidence

• Example of epigenetic mechanism: methylation → silencing gene expression
• Methyl molecules block transcription
• Evidence for long-term epigenetic effects
• Early adverse experiences → impact health and well-being [Provènzi et al., 2016]
• Childhood adversity of 9–12 year old girls [Papale et al., 2018]
• Ranging from mild to severe
• Methylation levels varied based on level of stress they experienced
• Possible avenue for cross-generational transmission of stress

Behavioural Genetics – Research Designs

• WHAT IS BEHAVIOURAL GENETICS?
  • Behaviour genetics: the science concerned with how variation in behaviour and development results from the combination of genetic and environmental factors
  • All behaviour traits are to some extent heritable
  • Individual differences somewhat influenced by genetic factors
  • Main goal: tease apart genetics and environment
  • 2 main premises:
  1. where genetic factors are important for a given trait or behaviour, individuals with similar genotypes should be phenotypically similar
  2. where environmental factors are important, individuals who were reared together should be more similar than people reared apart

QUANTITATIVE DESIGNS / FAMILY STUDIES

• Quantitative Behaviour Research Design
• Study naturally occurring genetic and environmental variation
• Comparing phenotypes of individuals who vary in amount of shared DNA
• Utilizes the ‘family study’ → correlations of phenotypic traits and genetics (degree of genetic relatedness)
• Correlations to compare individuals (i.e., does increased similarity = increased genetic overlap?)
• Different variations: Twin-study, Adoption study, Adoptive twin study

Twin Studies

• Identical vs. same-sex fraternal
• Identical = 100% shared DNA; fraternal = 50%
• Equal environments assumption
• Claim that twins that grow up together have an equal environment
• Assumption has been questioned
• If higher correlation for identical > fraternal → Genetic factors are substantially responsible

Quantitative Genetics – Adoption Studies

• Adoption study: Measures scores of adopted children on a given measure; compare to biological + adoptive parents
• More correlated with biological parents? or adoptive parents?
• Adoption study of adopted twins (Adoptive twin study): Identical twins who grew up together; Identical twins separated at birth
• Different environment = same environment?
• Genetic influence; Different environments < same environment?
• Environmental influence
• Major caveat: ‘sameness’ of environments → Phenotypes influence environment → Adoption agencies tend to place twins with similar families

HERITABILITY ESTIMATES & BIG PICTURE

• How much variability do genetic and environmental factors contribute?
• Behavioural geneticists use ‘heritability estimates’ from correlations
• Heritability: A statistical estimate of the proportion of the measured variance on a trait among individuals in a given population that is attributable to genetic differences among those individuals
• Exist for many psychological traits (e.g., personality, cognition, psychopathology)
• meta-analysis → 17,000 traits & 14 million twin pairs
• Heritability was greater than 0 for every trait investigated [Polderman et al., 2015]

INTERPRETING HERITABILITY

• Only apply to populations (NOT individuals)
• Example: 50% of population’s intelligence variation is due to genetics
• Apply to a particular population in a particular environment
• Example: height variation now vs. during famine (decrease in genetic → environment)
• Reflect the environments of the populations of individuals, NOT the trait itself
• Example: federally controlled education vs. state/province variation (higher in heterogeneous)
• Can change as a function of developmental factors (increase in choice!)
• Example: genetic contributions for intelligence increase in twins with age
• Do not imply immutability (especially when high)
• Primarily include WEIRD participants → (sampling bias)

ENVIRONMENT CONTRIBUTIONS

• When we estimate gene contribution we also get environment contribution!
• Shared environment: Family [Planalp et al., 2017]
• Birth Order? Favoritism?
• Siblings can differ in: Hobbies & interests – accident / condition – bullying – influential teacher
• Environment = many small effects working together
• Similar to polygenic inheritance for genetic effects
• Environment is more difficult to measure

BRAIN DEVELOPMENT: How development of brain structure occurs

NEUROGENESIS

• Neurogenesis: the proliferation of neurons through cell division
• 42 days after conception
• Adult humans can generate new neurons too! e.g., hippocampus
• Influenced by environmental factors (rewarding vs. threatening environments)
• Neuron birth → migration → grow axon and dendrites → specialization
• Myelination: the formation of myelin (a fatty sheath) around the axons of neurons that speeds and increases information-processing abilities
• Rapid at first, then slows down
• Certain areas are myelinated first – corresponding to maturation (e.g., sensory before frontal)

SYNAPTOGENESIS & SYNAPSE ELIMINATION

• 2. Synaptogenesis: the process by which neurons form synapses with other neurons, resulting in trillions of connections
• Timing and rate vary in different brain areas (e.g., sensory vs. frontal)
• 3. Synaptic pruning: the normal developmental process through which synapses that are rarely activated are eliminated
• Neurogenesis & Synaptogenesis make WAY more than necessary -- ~40\% need to be eliminated
• Different times in different areas
• Wave early in life & adolescence – paired with synaptogenesis
• Atypical patterns of pruning:
  • ASD → greater synaptic densities in certain areas
  • Schizophrenia → excessive pruning in adolescence

EXPERIENCE & PLASTICITY

• Which synapses will be pruned? → based on experience
• Increased activity = stronger connections = less likely to disappear
• Plasticity: the capacity of the brain to be affected by experience
• Recovery from injury
• Advantage for children (e.g., large cortex loss in children vs. adults)
• 2 types of plasticity:
  • Experience-expectant processes: the process through which the normal wiring of the brain occurs in part as a result of species-typical experiences
  • Experience-dependent processes: the process through which neural connections are created and reorganized throughout life as a function of an individual’s experiences

EXPERIENCE-EXPECTANT PROCESSES

• Particular niche → predictable experiences → brain development
• Pros: less hard-coded information (fewer genes) – rely on environment to shape/guide development
• Cons: heightened vulnerability if experiences they ‘expect’ don’t occur
• Example: Cross-modal reorganization
• Infants born with cataracts vs. deafness (visual and/or auditory input)
• Sensitive periods: timing is key for species-specific plasticity
• Window is opened and then gradually closes
• Activity that does or does not occur is typically irreversible

EXPERIENCE-DEPENDENT PROCESSES

• Brain is shaped by individual-specific experiences
• Animal models: Reared in complex vs. bare environments
• Better learning performance when brought up in complex environment [Sale, Berardi, & Maffei, 2009]
• Human studies: Individuals with highly specific experiences (e.g., musicians) [Choi et al., 2015]
• Wood wind instruments → increased cortical volume in areas related to lip movement (related to required expertise of this body area)