Chapter 3: Genetic Bases of Child Development Module 3.1 Mechanisms of Heredity Module 3.2 Genetic Disorders Module 3.3 Heredity is Not Destiny Children and Their Development, 3/e by Robert Kail

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

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

3.1 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

Sickle Cell Trait: An Example of Incomplete Dominance 3.1: Single Gene Inheritance

3.1 Behavioral Genetics Many behavioral genotypes reflect polygenic inheritance, which involves many genes Behavioral geneticists rely upon twin studies and adoption studies Cognitive abilities, psychological disorders, substance abuse, and personality are all affected by heredity

An Example of Polygenic Inheritance 3.1: Behavioral Genetics

3.2 Genetic Disorders Inherited Disorders Abnormal Chromosomes

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

3.2 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 (e.g., Turner’s Syndrome, Klinefelter’s Syndrome, XYY complement, XXX Syndrome) are caused by missing or extra sex chromosomes

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

3.3 Paths From Genes to Behavior Genes never cause behavior directly The behavioral consequences of genetic instructions depends on environment

3.3 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 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 Niche-picking: deliberately seeking environments that fit one’s heredity

3.3 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

The Relation Between Genes and Environment 3.3 The Nature of Nurture