Chapter 3: Genetic Bases of Child Development 3.1 Mechanisms of Heredity 3.2 Genetic Disorders 3.3 Heredity Is Not Destiny

3.1 Mechanisms of Heredity The Biology of Heredity Single Gene Inheritance Behavioral Genetics

The Biology of Heredity The first 22 pairs of chromosomes are autosomes and the 23rd pair are sex chromosomes Genotype is one’s complete set of genes and phenotype is one’s physical, behavioral, and psychological features 3.1 Mechanisms of Heredity

Single Gene Inheritance Pairs of alleles can be either homozygous or heterozygous Dominant allele: its chemical instructions are followed Recessive allele: its chemical instructions are ignored Incomplete dominance: one allele doesn’t dominate the other completely 3.1 Mechanisms of Heredity

Sickle Cell Trait: An Example of Incomplete Dominance

Behavioral Genetics Many behavioral genotypes reflect polygenic inheritance, which involves many genes. Behavioral geneticists rely upon twin studies and adoption studies. Intelligence, psychological disorders,and personality are all affected by heredity. 3.1 Mechanisms of Heredity

An Example of Polygenic Inheritance

3.2 Genetic Disorders Inherited Disorders Abnormal Disorders

Inherited Disorders Many disorders are triggered when a child inherits two recessive alleles. Examples include cystic fibrosis, PKU, and Tay-sachs disease Most inherited disorders are very rare. 3.2 Genetic Disorders

Abnormal Chromosomes Some people are born with too many, too few, or damaged chromosomes People with Down Syndrome usually have an extra 21st chromosome A number of disorders are caused by missing or extra sex chromosomes 3.2 Genetic Disorders

3.3 Heredity Is Not Destiny Paths from Genes to Behavior Reaction Range Changing Relations between Nature and Nurture The Nature of Nurture

Paths from Genes to Behavior Genes never cause behavior directly The behavioral consequences of genetic instructions depends on environment 3.3 Heredity Is Not Destiny

Reaction Range A genotype can lead to a range of phenotypes depending on the environment People with PKU genotype: those who eat normal diet will be mentally retarded, but those who eat special diet will have normal intelligence 3.3 Heredity Is Not Destiny

Reaction Range of Intelligence

Changing Relations between Nature and Nurture Passive G-E relation: parents pass on genotype and environment Evocative G-E relation: different genotypes evoke different responses from the environment Active G-E relation: actively seek environments related to their genes 3.3 Heredity Is Not Destiny

The Nature of Nurture Parents don’t provide exactly the same environments for all of their children (non-shared environmental influences) Parents provide the child’s genes and environment, but the child also influences her own environment 3.3 Heredity Is Not Destiny

The Relation Between Genes and Environment