Hereditary Influences on Development

Chapter 3

Outline 1. Genetic Principles

2. Genetic Diseases

3. Genes X Environment

Genetics

Each cell in the human body has 46 chromosomes (23 pairs)

Chromosomes are filled with DNA = Genetic Blueprint

Genes

Specific segment of DNA, responsible for the production of a specific protein

Allele: Part of a gene; 2 alleles per gene

Genes Work in pairs

Homozygous (Same) Heterozygous (Different)

Basic Terminology XX = Female XY = Male

Genes

Genotype Set of genetic traits a person inherits;

the genetic blueprint

Phenotype Set of traits a person actually displays

Genes Dominant Genes

Recessive Genes

Genes Example of Dominant and

Recessive Genes (eye color, hair color)

Chromosome Abnormalities An error occurs during cell division

Down’s Syndrome (Trisomy 21), an extra 21st chromosome

Any changes in genetic info (extra or less) = Abnormality

Sex Chromosome Disorders 1. Turner Syndrome X_

2. Kleinfelter’s Syndrome XXY

3. Fragile X xX or xY

Single Gene Defects

1. Autosomal Recessive

Inherit recessive allele from both parents

E.G. PKU

2. Autosomal Dominant

Only need to inherit 1 allele, from either parent

E.G. Huntington’s Disease

3. Recessive genes on the X chromosome

Sex linked E.g. Hemophilia

Sickle Cell Anemia

Think about yourself: How sociable are you?

How athletic are you?

Models of Gene-Environment Interaction

Reaction Range (Gottesman)

Degree to which variations in the environment influence genotype

Behavioral Genetics

Robert Plomin

Studies the influence of genetic factors on behavioral traits

Gene-Environment Correlations

Scarr and McCartney (1983)

1. Passive 2. Evocative 3. Active

Behavioral Genetics

1. Twin Studies MZ vs DZ (Identical vs Fraternal)

Identical = 100% genetic similarity Fraternal = 50% genetic similarity

Behavioral Genetics

Heritability = Proportions of variance due to variations in genotypes

Behavioral Genetics

2. Adoption Studies

3. Family Studies E.G. Schizophrenia

Non-shared Environment Unique environment in which each

child (even in the same family) lives

Unique parent-child interaction Different school experiences Different peer group