Transcript Chapter 3

Chapter 3: Genetic Bases
of Child Development
MODULES
3.1 Mechanisms of Heredity
3.2 Genetic Disorders
3.3 Heredity Is Not Destiny
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Module 3.1 Mechanisms
of Heredity
LEARNING OBJECTIVES
Define chromosomes and genes.
Explain the mechanism of heredity
for dominant and recessive traits.
Understand how heredity
influences behavioral and
psychological development.
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The Biology of Heredity
Father’s sperm +
(gamete)
Mother’s egg
(gamete)
46 chromosomes total
• 23 from each parent
Meiosis: the biological process of cell division resulting in gametes that have 23 chromosomes, which is
half the amount of genetic material normally seen in a human cell.
Mitosis: the biological process of cell division resulting in bodily cells that are exact copies of their parent
cells and have a full set of 46 chromosomes.
In-vitro fertilization: an artificial form of egg fertilization in which sperm and egg are united in a
laboratory dish.
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The Biology of Heredity
The first 22 pairs of chromosomes are autosomes
and the 23rd pair are sex chromosomes.
Chromosomes consist of Deoxyribonucleic acid
(DNA) which codes for proteins and enzymes.
Genotype is one’s complete set of genes and
phenotype is one’s physical, behavioural, and
psychological features.
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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.
Single nucleotide polymorphism (SNP): a change
in the normal nucleotide base at a particular
location within a strand of DNA.
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Sickle Cell Trait: An Example
of Incomplete Dominance
Endogamy: a preference for mating with
people from one’s own social or cultural
group.
Clinical variation: continuous genetic
variation observed.
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Behavioural Genetics
The study of the inheritance of behavioral and
psychological traits.
Many behavioural genotypes reflect polygenic
inheritance, which involves many genes.
Behavioural geneticists rely upon twin studies
(monozygotic and dizygotic) and adoption studies.
Intelligence, psychological disorders (i.e.
depression and schizophrenia),and personality
(introversion/extroversion) are all strongly affected
by heredity.
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An Example of Polygenic
Inheritance
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The Nature of Nurture
Parents don’t provide exactly the same environments for
all of their children (non-shared environmental influences).
– Non-shared environmental influences
 Experiences unique to individual, not shared by
other members of family in same environment.
– Shared environmental influences
 Experiences common to all family members in same
environment.
Parents provide the child’s genes and environment, but
the child also influences her own environment.
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The Nature of Nurture
The family environment is important, but
it usually affects each child in unique
ways, which makes siblings differ.
Families create multiple, unique
environments for each child in the
household.
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Module 3.2 Genetic
Disorders
LEARNING OBJECTIVES
List a number of disorders that are
inherited.
State what disorders are caused by too
many or too few chromosomes.
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Inherited Disorders
Inherited disorders that affect development
are usually triggered when a child inherits
two recessive alleles.
Examples include Albinism, Cystic fibrosis,
PKU, and Tay-Sachs disease.
Most inherited disorders are very rare.
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Abnormal Chromosomes
Some people are born with too many, too few, or
damaged chromosomes.
People with Down Syndrome usually have an
extra 21st chromosome.
Damaged autosomes always affect development
because autosomes contain so much genetic
material.
A number of disorders are caused by missing or
extra sex chromosomes (see Table 3-5).
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Module 3.3 Heredity Is
Not Destiny
LEARNING OBJECTIVES
Describe how genes affect behaviour.
Explain whether one genotype always leads to
the same phenotype.
Understand how the relationship between
heredity and environment changes as children
develop.
Trace how family environments influence
children’s development.
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Paths from Genes to
Behaviour
Genes never cause behaviour
directly.
The behavioural consequences of
genetic instructions depends on
the environment.
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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 cognitively delayed, but
those who eat special diet will have normal
intelligence.
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Reaction Range of Intelligence
Source: Gottesman, 1963
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Changing Relations between
Nature and Nurture
Passive gene-environment relation: parents pass on
genotype and environment.
Evocative gene-environment relation: different
genotypes evoke different responses from the
environment.
Active gene-environment relation: actively seek
environments related to their genes.
Niche-picking: the process of deliberately selecting
an environment suitable to one’s genotype.
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The Relation Between Genes
and Environment
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Conclusions
Parents are the source of children’s
genes and the primary source of young
children’s experiences both shared
and non-shared environments.
Intricate link between nature, nurture
and all aspects of child development.
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