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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