Chapter 2:

Genetic Bases of Child Development

Chapter 2: Genetic Bases of Child Development

Chapter 2 has two modules:

Module 2.1 Mechanisms of Heredity

Module 2.2 Heredity, Environment, and Development

Mechanisms of Heredity

The Biology of Heredity

A Quick Review• Cell • Sperm• Egg• Chromosome• DNA

The Biology of Heredity

Chromosomes• Autosomes• Sex chromosomes

Gene• Genotype • Phenotype

Single Gene Inheritance

Genes come in different forms known as alleles

• Homozygous or heterozygous• Dominant or recessive allele• Incomplete dominance

Think about these terms as you look at the next slide.

Sickle Cell Trait: An Example of Incomplete Dominance

Do you see why?

• Individuals with one dominant and one recessive allele have the SC trait.

Genetic Disorders: Inherited

• Often triggered through inheritance of two recessive alleles

• Inherited disorders (Table 2.2)

Genetic Disorders: Chromosomes

• Too many, too few, or damaged chromosomes

• Abnormal chromosome numbers (Table 2.3)

Heredity, Environment, and Development

Behavioral Genetics

Behavioral genetics: inheritance of behavioral and psychological traits

• Polygenic inheritance

Let’s look at an example on the next slide.

An Example of Polygenic Inheritance

• Phenotypes distribute with extremes at both ends

• Combined activities of many separate genes

Methods of Studying Behavioral Genetics Twin studies and adoption studies•Compare identical and fraternal twins or adoptive and biological siblings to measure the influence of heredity

•If identical twins are more alike than fraternal twins, this implicates heredity.

Behavioral Genetics

True or false?

Cognitive abilities, psychological disorders, substance abuse, and personality are all affected by heredity.

Behavioral Genetics

Plomin’s Adoption StudiesChild intelligence correlated more stronglywith biological mother’sintelligence than adoptive mother’s intelligence

Hereditary and environmental contributions to intelligenceproposed

And so…

Heredity and environment interact dynamically throughout development.

Paths From Genes to Behavior

Behavioral consequences of genetic instructions

• Depend on environment in which those instructions develop

• Reaction range

• Heritability coefficient

Paths From Genes to Behavior

What are the paths?

Paths From Genes to Behavior

Epigenesis• Continuous interplay between gene and

multiple levels of environment drives development

• Heritability coefficient

Paths From Genes to Behavior

Niche-picking• Deliberately seeking environments that fit

one’s heredity

Take a minute to think about environments you sought out as a child.

What was your niche?

2.2 Paths From Genes to Behavior

Why aren’t all children in the same family identical?

• Environmental influences

• Non-shared environmental influences

• Child influences

The Relation Between Genes and Environment