LESSON 6: Behaviour Genetics - Predicting Individual Differences

Behavior Genetics

The study of the relative power and limits of:

• Genetic influences

• Environmental influences on behavior.

Environment

Every external influence including:

• Prenatal nutrition

• Family

• Friends

• Culture

• Education

• Life experiences

Chromosomes

Threadlike structures made of DNA that contain genes.

DNA

• Deoxyribonucleic Acid

• Genetic blueprint of life

Genes

• Units of heredity

• Segments of DNA

• Provide instructions for making proteins

Genome

Complete set of an organism's genetic information

46

Total number of chromosomes

20,000–25,000 genes

Approx total number of Human Genes

• Proteins

• Body tissues

• Biological processes

Genes provide instructions for producing:

Genetic variation

Genetic variation helps explain why people differ in:

• Height

• Disease susceptibility

• Intelligence

• Personality

• Aggressiveness

• Happiness

Genotype

The genetic makeup a person inherits.

Phenotype

Observable characteristics resulting from:

• Genes (genotype)

• Environment

Example of Genotype

Genetic potential for height

Example of Phenotype

Actual height achieved

Identical Twins

(Monozygotic)

• One fertilized egg

• Splits into two

• Share nearly 100% of genes

Fraternal Twins

(Dizygotic)

• Two fertilized eggs

• Share about 50% of genes

• Similar to ordinary siblings

Mirror Twins

• Left-handed vs right-handed

• Opposite facial moles

• Opposite dominant eye

Divorce Study

Researchers studied:

1,500 twin pairs

Findings:

Fraternal twin divorced → 1.6x greater risk

Identical twin divorced → 5.5x greater risk

Estimated:

• 50% of divorce risk may be attributable to genetic factors.

• (Use as illustration only, not evidence that divorce is genetically determined.)

Separated Twins

Famous Case: The Jim Twins

Separated shortly after birth but shared:

• Similar habits

• Similar interests

• Similar personality traits

• Similar health characteristics

Significance

Evidence for strong genetic influence.

The Jim Twins

Separated shortly after birth but shared:

• Similar habits

• Similar interests

• Similar personality traits

• Similar health characteristics

Adoption Studies

Nature's Second Experiment

Molecular Genetics

Study of:

• Molecular structure of genes

• Functions of genes

Goal of Molecular Genetics

Identify specific genes involved in behaviour.

HERITABILITY

The proportion of variation among individuals that can be attributed to genetic differences

Epigenetics

Study of environmental influences on gene expression without changing DNA itself.

Rat Studies

Maternal care affects stress responses.

Human Studies

Childhood abuse is associated with epigenetic changes.