Chapter 5: Genetics in Psychology

Learning Objectives

• Define Behavioral Genetics.

• Differentiate hereditary and environmental determinants of behavior.

• Distinguish between Genotype and Phenotype.

• Identify different Mutations and Genetic Abnormalities.

Nature vs. Nurture

Nature

• Refers to heredity, the transmission of physical and psychological characteristics from parents to offspring through genes.

Nurture

• Refers to the environment that influences development.

Definition of Genetics

• Genetics is a branch of biology focused on genes, genetic variation, and heredity in organisms.

• Explores gene function, variation, and transmission from parents to offspring.

What is Behavioral Genetics?

• Field that studies the biological basis of behavior.

• Determines the extent of behavioral differences due to genetic factors.

• Explores the influence of heredity on personality traits, mental abilities, and psychological disorders.

Heritability

• Refers to how much of the variations in a trait among individuals is due to genetic differences.

Misconceptions about Heritability

• Does not indicate the percentage of a trait due to genes vs. environment.

• A high heritability score does not identify the specific genes or environmental factors involved.

• Familial traits can be influenced by lifestyle/environment, not just genetics.

• High heritability does not imply a trait is resistant to change (e.g., hair color).

Genes: The Codes for Life

• Chromosomes containing DNA are located in the nucleus of cells.

• DNA segments, or genes, encode proteins affecting development.

Genome

• The complete set of instructions for making an organism, encompassing all its genes.

Genes 101

• Dominant Gene: Influences a specific trait; can mask a recessive gene.

• Recessive Gene: Only expressed when paired with another recessive gene.

• Genotype: The inherited gene set, forming a unique blueprint.

• Phenotype: Observable expression of genes influenced by environmental factors.

Polygenic Inheritance

• Involves multiple genes interacting to determine a trait.

Sexual Reproduction and Genetic Transmission

• Chromosomes are DNA molecules containing thousands of genes (23 pairs form a zygote).

• Genes serve as blueprints for protein synthesis (units of heredity).

Cell Division

Somatic Cells

• Mitosis: Process where somatic cells replicate and divide, producing identical cells.

Germ Cells

• Meiosis: Ensures genetic diversity through replication and two division steps with processes like crossing over.

Heritability of Intelligence: History

• Francis Galton’s study linked intellectual achievement to genetic differences but failed to consider environmental factors.

• Advocated for selective breeding influenced by later controversial ideologies.

Heritability of Intelligence: Kinship Studies

• Twin Methods: Studies correlations of IQ among twins with varying degrees of genetic relation.

• Adoptive Methods: Evaluates correlations among individuals sharing environments without genetic ties.

Mutations/Genetic Abnormalities

• Mutations: Errors in gene replication, potentially leading to abnormalities (e.g., Down Syndrome, PKU, Klinefelter syndrome).

What is Epigenetics?

• Explores how environmental influences affect gene expression and development.

• Highlights the dynamic interplay of genes and experiences in shaping behavior, health, and achievement.

Epigenetics and Lifelong Impact

• Early experiences can rearrange epigenetic marks that guide gene expression affecting traits and behaviors.

• Positive experiences can lead to beneficial epigenetic changes, while negative influences can leave lasting impacts.

• Stress reduction and supportive relationships are crucial for optimal brain development.