Biological Bases of Behaviour: Genetics, Nervous System, and Brain Development

Biological Psychology

Introduction

Biological psychology examines how biological processes influence human behaviour. Two key areas are the genetic basis of behaviour and the neurological basis of behaviour.

• Genetic basis of behaviour: Focuses on how heredity shapes human behaviour.

• Neurological basis of behaviour: Explores the role of the brain in behaviour.

Genetic Basis of Behaviour

Overview

Psychologists investigate whether behaviours or characteristics, such as intelligence, are influenced by genetic inheritance or environmental factors. Twin and adoption studies provide evidence for genetic determination, but research also shows the environment plays a significant role.

• Genetic inheritance: Transmission of traits from parents to offspring via genes.

• Environmental influence: Non-genetic factors affecting behaviour.

Principles of Hereditary Transmission

Chromosomes and Genes

Hereditary transmission involves the passage of genetic information through chromosomes and genes.

• Chromosomes: Structures that store and transmit genetic information. Each contains genes and is shaped like a double helix.

• DNA: The substance of which chromosomes are made.

• Gene: Segment of DNA coding for amino acids. Four types: A, C, G, T.

• Alleles: Alternative forms of a gene, one from each parent.

• Simple dominant and recessive inheritance: Some alleles are stronger (dominant) than others (recessive).

Behavioural Genomics

Behavioural genomics explores how genetic variations influence behaviour, personality, and mental health. The Human Genome Project mapped over 3 billion DNA bases, identifying thousands of genes linked to behaviour.

• Genomic research aids in understanding traits, mental health, and treatment.

Epigenetics

Epigenetics studies how environmental factors alter gene expression, with changes potentially affecting future generations.

• Gene expression can be modified by experiences and environment.

• Behaviour and experiences can affect gene expression.

• Epigenetic changes can be inherited.

Methylation

Methylation is a biochemical process that can reduce or silence gene expression, often triggered by environmental factors.

• Involves chemical modification of DNA.

• Can affect cell division and gene activity.

Gene Expression - CRISPR

CRISPR is a tool for editing genes, with potential for targeted treatment of diseases and ethical implications.

Genotype and Phenotype

Definitions

• Genotype: The genetic makeup of an individual; the set of genes inherited from parents.

• Phenotype: Observable characteristics resulting from the interaction of genotype and environment.

Genotype vs. Phenotype

• Genotype provides the potential for traits.

• Phenotype is the actual expression, influenced by environment.

• $\text{Genotype} + \text{Environment} = \text{Phenotype}$

Example: Height

• Genotype sets the maximum potential height.

• Environmental factors (e.g., nutrition) influence actual height.

Principles of Hereditary Transmission

Cell Division

• Mitosis: Process of normal cell division.

• Meiosis: Cell division creating gametes (sex cells), halving chromosome number. Fertilization restores chromosome count.

Behavioural Genetics

Overview

Behavioural genetics studies how genes and environment influence behaviour, often using twin and adoption studies.

• Compares people of different relatedness (siblings, strangers).

Twin Studies

• Monozygotic twins: Formed from one fertilized egg splitting into two embryos; genetically identical.

• Dizygotic twins: Formed from two separate eggs fertilized by different sperm cells; genetically similar as siblings.

Twins and Phenotype

• Identical twins have the same genotype but may differ in phenotype due to environmental factors.

Adoptive Studies

• Compare traits between adopted children and their biological/adoptive parents to separate genetic and environmental influences.

What Could Twin and Adoptive Studies Determine?

Different DNA, Same Environment	Same DNA, Different Environment
If intelligence is the same, it must be due to environment. If intelligence is different, it must be due to genetics.	If intelligence is different, it must be due to environment. If intelligence is the same, it must be due to genetics.

Nervous System

Main Functions

• Receiving input from the senses

• Processing information by relating it to previous experiences

• Producing and monitoring bodily actions

Divisions of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord.

• Peripheral Nervous System (PNS): Nerves outside the CNS, including somatic and autonomic systems.

Somatic Nervous System

• Processes sensory information

• Controls voluntary muscle movement

Autonomic Nervous System

• Regulates organs, glands, and biological processes

• Sympathetic: Fight, flight, freeze response

• Parasympathetic: Rest and recovery

Central Nervous System Organization

• Divided into regions based on location and function

• Complex tasks require coordination across regions

Cell Types in the Nervous System

• Neurons: Specialized for rapid signaling; about 86 billion in the brain.

• Glial cells: Support neurons, help growth, maintain chemical environment.

Importance of Neurotransmitters

• Chemical messengers enabling neuron communication

• 8 key neurotransmitters identified (e.g., serotonin, dopamine)

Neuron Communication

• Neurons communicate via axons and dendrites

• Neurotransmitters transmit signals between neurons

Synaptic Transmission

• Synapses are junctions where neurotransmitters are released

• Drugs can affect neurotransmission

The Action Potential of Neurons

• Resting potential: Neuron at rest has a negative charge inside

• Action potential: Stimulation causes positive charge to flow in, triggering a signal

• After firing, neuron returns to resting potential

The Endocrine System

Overview

The endocrine system consists of glands that secrete hormones into the bloodstream, influencing behaviour and bodily functions.

• Major glands: Hypothalamus, pituitary, pineal, thyroid, adrenal, pancreas, ovaries/testes

• Hormones contribute to homeostasis (energy, metabolism, temperature)

Brain Development and Plasticity

Developmental Changes

• At birth, brain size is close to adult size

• 90% of brain development occurs before age 5

• Brain grows in spurts; different systems develop at different rates

• Brain weight declines after age 30; about 5% lost per decade after 40

• Communication between regions may decrease with age

• Decreased lateralization between hemispheres

Neuroplasticity

• Capacity of the brain to change and rewire itself

• Damaged neurons can sprout new dendrites and re-establish connections

• Axons can regenerate and grow

• Reorganization of brain function

• Key research areas: spinal cord injury, Parkinson's, stroke, dementia