Chapter 3 - Biology And Behaviour (Lecture 3)

Front 1

Nature and Nurture

Back 1

- Both heredity and environment influence individual' characteristics
- Individuals differ from one another by only about 1 to 1.5% of their genes
- Each person has the same set of genes, just differences from slight variations

Front 2

Genotype

Back 2

The genetic material an individual inherits

Front 3

Phenotype

Back 3

The observable expression of the genotype, including body characteristics and behaviour

Front 4

Environment

Back 4

Includes every aspect of the individual, and his or her surroundings, other than genes

Front 5

Four Fundamental Relations

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- Parents' genetic contribution to the child's genotype
- Contributions of the child's genotype to his or her own phenotype
- Contributes of the child's environment to his or her phenotype
- Influence of the child's phenotype on his or her environment

Front 6

Relation 1: Parents' and Child's Genotype

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- Genetic Material is passed on by chromosomes
- Carry all the instructions involved in the formation and functioning of an organism

Front 7

Genes

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Sections of chromosomes; basic units of heredity for all living things

Front 8

Sex Determination

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Sex chromosomes determines an individual's biological sex

- Females have two X chromosomes in the 23rd pair, whereas males have XY
- X Chromosomes have 3x more genes than Y
- A gene on the Y chromosome encodes the protein that triggers the formation of the testes, which produce testosterone, which produces male body features

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Why are children of the same two parents so genetically diverse?

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- Mutations: changes in sections of DNA caused by random or environmental factors
- Crossing over: sections of DNA switch from one chromosome to another during sex cell production, further increasing genetic variability
- Random assortment: chance determines which member of each pair of chromosomes into the new sperm or egg

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Relation 2: Child's Genotype and Phenotype

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One some of those a person's genes are expressed at any one time

Front 11

Gene Expression

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About a third of human genes have two or more different forms, known as alleles

- The recessive allele is the form of the gene that is expressed if present
- The recessive allele is not expressed if a dominant allele is present
- A person who inherits two of the SAME alleles for a trait = homozygous
- A person who inherits two DIFFERENT alleles for a trait = heterozygous

Front 12

Polygenic Inheritance Patterns

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When traits are governed by more than one gene, applies to most traits and behaviours of interest to behavioural scientists

Front 13

Relation 3: Child's Environment and Phenotype

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The environment plays a role in how the phenotype is expressed

Front 14

The Case of MAOA (Environment + Genotype)

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- Severe maltreatment increases likeliness of antisocial behaviour
- Stronger for those individuas who had a relatively inactive MAOA gene

Front 15

Environment and Phenotype: PKU

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- Children with phenylketonuria (PKU) - a chromosome 12 disorder - cannot process phenylalanine
- A phenylalanine-free diet can prevent mental retardation from PKU

Front 16

Genetic Transmission of Diseases and Disorders

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Sex-Linked Inheritance: male-pattern baldness, red-green colour blindness, hemophilia, fragile-X syndrome
Chromosomal anomalies: Down syndrome (trisomy 21), Kleinfelter syndrome (XXY), Turner Sydrome (XO)

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Relation 4: Child's Phenotype and Environment

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- Children are active creators of their environments
- They evoke certain kinds of responses from others
- They select surroundings and experiences that support their interest, talents, and personality characteristics

Front 18

Behavioural Genetics Research Designs

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The Family Study: measure trait of interest among people who vary in genetic relatedness

Looks at how a trait varies across people who:
- Are genetically more similar AND/OR
- Share the same environment

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Types of Family Studies

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- Twin-Study Designs: Compare frequency of trait-sharing between monozygotic and dizygotic twins
- Adoption Studies: Are adopted children more like their biological or their adopted relatives (for a particular trait)?
- Identical Twins Reared Apart: Monozygotic twin siblings who have not met since they were infants

Front 20

Heritability Estimates

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A statistical estimate which relates variability in a trait to variability in genetic differences between individuals

Front 21

Limitations of Heritability Estimates

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- Applies only to populations, not individuals
- Applies only to a particular group living at a particular time
- Can differ for groups of people who grow up in very different environments
- High heritability does not imply immutability
- Says nothing about differences between groups

Front 22

Environmental Effects

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- Most obvious source of shared environment is growing up together in the same family
- Non-shared environment effects include experiences unique to the individual
- Siblings may have quite different experiences unique to the individual
- Experience outside the family may be very different
- The primary effect of non-shared environmental factors is to increase the differences among family members

Front 23

Brain Development

Back 23

Synaptogenesis: each neuron forms synapses with thousands of other neurons, forming of trillions of connections in the brain

- Synaptogenesis produces too many synapses
- Synaptic Pruning (Elimination): occurs at different times in different areas of the brain and continues until adolescence, it is experience dependent

Front 24

The Importance of Experience

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Plasticity is the capacity of the brain to be affected by experience

- Experiences influences which synapses will be pruned and which will be maintained
- Synapses that are frequently activated are preserved: "neural Darwinism"

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Experience-Expectant Processes

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Experience-expectant plasticity: the normal wiring of the brain that occurs as a result of typical experiences

Examples: language learning, normal vision

- If the expected experience is not available then development will be impaired

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Sensitive Periods

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- stimulus-specific
- A key element in experience-expectant plasticity is timing

Front 27

Experience-Dependent Processes

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Experience-Dependent plasticity: neural connections are created and reorganized throughout life according to experience

Front 28

Brain Damage and Recovery

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- Timing and plasticity play important roles in recovery from brain damage
- The effects of brain damage depend on what is happening in the brain at the age
- The greatest plasticity is observed when synapse generation and pruning are occurring during early childhood

Front 29

Emergent Effects of Early Brain Damage

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The effects of brain damage may be revealed over time (sleeper effects)