CHILD PSYCHOLOGY
Second Canadian Edition
Vasta, Younger, Adler, Miller, Ellis
Prepared by:
Mowei Liu
Chapter 3
Genetics: The Biological Context of
Development
Learning Objectives
• Learning Objective 3.1 Identify and describe the
mechanisms and processes by which physical and
behavioural characteristics are inherited.
• Learning Objective 3.2 Describe different types of
genetic disorders and their impact on child
development.
• Learning Objective 3.3 Describe the influence that
genes have on the development of psychological
abilities and traits.
• Learning Objective 3.4 How do genes and
environment interact to influence the development
of behaviour?
Mechanisms of Inheritance: Cell Division
• Cells are comprised of three divisions:
– Nucleus contains the chromosomes
• Chromosomes: strands of the genetic material DNA
– Each human cell contains 23 chromosome pairs
(yielding 46 total chromosomes per cell)
– Autosomes comprise 22 of the 23 pairs
– Sex chromosomes comprise the 23rd pair
• Males are XY, females are XX
– Cytoplasm fills the cell interior
– Cell membrane encases the cell
Mechanisms of Inheritance: Cell Division
• Cells form two groups based on function:
– Body cells: form the structures of the body
• Reproduce by mitosis: Forming two identical cells,
each equipped with 23 pairs of chromosomes
– Germ cells: form the reproductive cells
• Reproduce by meiosis: forming four cells with each
cell containing only 23 chromosomes
• These cells are the gametes: ova or sperm
• During conception, a sperm merges with an ovum to
form a new cell containing 23 pairs of chromosomes
• Mitosis refers to a
process by which 2
identical cells are
produced
• Meiosis refers to a
process in 4 cells
are produced, with
each containing only
23 chromosomes
Figure 3.1 (Mitosis and meiosis. Mitosis
results in two cells identical with the parent and
with each other. Meiosis results in four cells
different from the parent cell and from each
other. Adapted from Biology: Exploring Life
(p.152) by G. D. Brum & L. K. McKane, 1989,
New York: John Wiley & Sons. Adapted by
permission of the authors.
Mechanisms of Inheritance: Cell Division
• Crossing over:
During meiosis,
the x-shaped
chromosomes line
up and intermix,
yielding a novel
genetic product
Figure 3.2 Crossing over results in the exchange
of genetic material. After the cross-over, all four
strands are different. Adapted from Biology:
Exploring Life (p. 44) by G. D. Brum & L. K.
McKane, 1989, New York: John Wiley & Sons.
Adapted by permission of the authors.
Inside the Chromosome
• DNA: the basic genetic
material, formed from
pairs of base nucleotides
– The bases form pairs
such as adenosinethymine or guaninecytosine
– The DNA strand is in the
form of a double helix
made up of a series of
base pairs
Figure 3.3 Structure and Replication
of DNA
Mendel’s Studies: Principles of Heredity
• Mendel argued that certain traits are transmitted
from parents to child
– Each trait is governed by two elements with one
from each parent
– Phenotype: the expressed trait
– Genotype: the underlying genes that govern the trait
Mendel’s Studies: Principles of Genetic
Transmission
• Principle of dominance: Some genes are always
expressed (dominant gene), others are recessive
(recessive gene)
• Polygenic inheritance occurs when traits are
determined by a number of genes
• Incomplete dominance occurs when the dominant gene
does not completely suppress the recessive gene
• Codominance occurs when both genes are dominant
and thus both are expressed
Mendel’s Studies: Common Genetic Traits
Dominant
Recessive
Brown eyes
Normal hair
Dark hair
Normal colour vision
Freckles
Dimples
Free earlobes
Double-jointed thumbs
Blue, gray, or green eyes
Baldness (in men)
Blond hair
Colour blindness
No freckles
No dimples
Attached earlobes
Tight thumb ligaments
Genetic Disorders: Hereditary Disorders
• Mutations (genetic variations) can be adaptive or
maladaptive
• Dominant disorders
– Huntington’s chorea: a fatal syndrome in which
the nervous system degenerates in adulthood
(age 30-40)
Genetic Disorders: Hereditary Disorders
• Recessive disorder
– Diseases with errors of metabolism
• Tay-Sachs disease: a fetal disease in which the
nervous system disintegrates because the body
cannot break down fats in brain cells
• Phenylketonuria (PKU): an inherited disease in
which the body cannot process the amino acid
phenylalanine
– Treatment: Eat a diet low in this amino acid during
critical periods of brain development
– Diseases without errors of metabolism
• Sickle-cell anemia (SCA)
Sickle-Cell Anemia (SCA)
Figure 3.5 Scanning electron micrographs of red blood cells from normal
individuals (left) and individuals with sickle-cell anemia (right). (Bill Longcore/Photo
Researchers, Inc.)
Structural Defects in the Chromosome
• Autosomal disorders:
– Down syndrome
• The 21st pair of chromosomes has a third member
• Results in mental retardation, poor muscle tone, and
distinctive facial features
• Greatest risk occurs in mothers between the ages of
45-49 years
Structural Defects in the Chromosome
• Disorders of the sex chromosomes:
– Fragile X syndrome
• Caused by an abnormal gene on the X chromosome.
• Results in a variety of physical and behavioural
symptoms, including mental retardation
– Turner’s syndrome occurs when a female has only one
X chromosome (XO)
– Klinefelter’s syndrome occurs when a male inherits an
extra X chromosome (XXY)
Studying the Effects of Genes on Behaviour
• Three principal areas of behaviour
– Intellectual abilities
– Psychiatric disorders including children’s behaviour
problems
– Personality
• Four major approaches are used to study the
impact of genes on behaviour
– Family studies
– Adoption studies
– Twin studies
– Combined Twin Study and Adoption Study
Family and Adoption Studies
• Family studies compare different family members
and their similarity in certain characteristics
– Explores whether the phenotypic similarity on a trait
follows the genotypic similarity among the people
being compared
• Adoption studies compare similarities in
characteristics between adopted children and their
biological and adoptive parents
– Explores the contribution of shared genes versus
shared environment to a trait
Twin Studies
• Two types of twins:
– Identical twins: Monozygotic (MZ) – from the
same fertilized egg
– Fraternal twins: Dizygotic (DZ) – from two
different eggs
• Twin studies compare the similarity between the
twins in regard to a behaviour
– Concordance: the degree of similarity of twins on
a behavior
– Most studies indicate that MZ twins show greater
similarity than do DZ twins and this effect is larger
as they get older
Twin Studies
Age-Related Changes in Concordance for MZ and DZ Twins
Figure 3.7 Concordance in IQ changes in (a) identical, or monozygotic (MZ), twins and (b)
fraternal, or dizygotic (DZ), twins from 3 months to 6 years of age.The scales are different to
accommodate different ranges of scores.The important point is that changes in performance are
more similar for monozygotic twins. Adapted from “The Louisville Twin Study: Developmental
Synchronies in Behavior” by R. S.Wilson, 1983, Child Development, 54, p. 301. Copyright © 1983
by The Society for Research in Child Development, Inc. Adapted by permission.
Models of Gene-Environment Interaction
• Gottesman’s limit-setting model: Range of ability is
determined by genes – actual value of that ability is
determined by the environment (range of reaction)
Range of Reaction Model
Figure 3.9 The reaction range concept, showing the simultaneous influences of genes and environment.
Adapted from “Developmental Genetics and Ontogenetic Psychology: Overdue Détente and Propositions
from a Matchmaker” by I. I. Gottesman, 1974. In A. D. Pick (Ed.), Minnesota Symposia on Child Psychology,
vol. 8, p. 60, University of Minnesota Press. Copyright © 1974 by the University of Minnesota. Adapted by
permission.
Models of Gene-Environment Interaction
• Scarr’s niche-picking model:
– Passive gene-environment correlation
– Evocative gene-environment correlation
– Active gene-environment correlation
• Plomin’s environmental genetics model: Different
children experience the same environment
differently (nonshared environment)
• Bronfenbrenner and Ceci’s biological model: Child’s
genes and immediate environment interact
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