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Child Psychology:
The Modern Science, 3e
by
Vasta, Haith, and Miller
Paul J. Wellman
Texas A&M University
John Wiley and Sons, Inc. © 1999
PowerPoint  Presentation: Chapter 4
Genetics: The Biological
Context of Development
Cell Chromosomes

Cells are comprised of 3 divisions:
– Cell membrane encases the cell
– Cytoplasm fills the cell interior
– Nucleus contains the chromosomes

Chromosomes are 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
© 1999 John Wiley and Sons, Inc.
Divisions of the Cell
© 1999 John Wiley and Sons, Inc.
Vasta, 3e Fig. 4.1
Cell Function

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
© 1999 John Wiley and Sons, Inc.


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 adapted with permission from Biology: Exploring Life,
by G.D. Brum and L.K. McKane, 1989, New York: John Wiley and Sons)
© 1999 John Wiley and Sons, Inc.
Vasta, 3e Fig. 4.2
Cross-Over During Meiosis

During meiosis,
the x-shaped
chromosomes
line up and
intermix, yielding
a novel genetic
product
(Figure adapted with permission from Biology: Exploring Life,
by G.D. Brum and L.K. McKane, 1989, New York: John Wiley and Sons)
© 1999 John Wiley and Sons, Inc.
Vasta, 3e Fig. 4.3
DNA

DNA is the basic genetic
material, formed from
pairs of base nucleotides
– The bases form pairs such
as adenosine-thymine or
guanine-cytosine
– The DNA strand is in the
form of a double helix
made up of series of base
pairs
© 1999 John Wiley and Sons, Inc.
Vasta, 3e Fig. 4.4
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 refers to the expressed trait
– Genotype refers to the underlying genes
that govern the trait

Principle of dominance: Some genes
are always expressed, others are
recessive
© 1999 John Wiley and Sons, Inc.
Mendelian Inheritance
© 1999 John Wiley and Sons, Inc.
Vasta, 3e Fig. 4.5
Common Genetic Traits
DOMINANT
Brown eyes
Normal hair
Dark hair
Color vision
Freckles
Dimples
© 1999 John Wiley and Sons, Inc.
RECESSIVE
Blue, gray, or green eyes
Baldness (in men)
Blond hair
Color Blindness
No freckles
No dimples
Genetic Disorders

Dominant disorders:
– Huntington’s chorea refers to a fatal
syndrome in which the nervous system
degenerates in adulthood (age 30-40)

Recessive disorders:
– Phenylketonuria (PKU) refers to 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
© 1999 John Wiley and Sons, Inc.
Gene-Environment Interaction
(Figure adapted with permission from “Developmental Genetics and Ontogenetic Psychology: Overdue
Détente and Propositions from a Matchmaker” by I. Gottesman, 1974. In A.D. Pick (Ed.),
Minnesota Symposium on Child Psychology, vol. 8, p 60. Copyright © 1974 by the University of Minnesota Press.)
© 1999 John Wiley and Sons, Inc.
Vasta, 3e Fig. 4.8
Gene-Behavior Studies

Four major approaches are used to study
the impact of genes on behavior
– Family studies
– Adoption studies
– Twin studies
– Twins raised apart studies

Three principal areas of behavior
– Intellectual abilities
– Psychiatric disorders including schizophrenia
– Personality
© 1999 John Wiley and Sons, Inc.
Twin Studies

Twins are either derived from the same
fertilized egg or a different egg
– Identical twins: Monozygotic (MZ)
– Fraternal twins: Dizygotic (DZ)

Twin studies compare the similarity
between the twins in regard to a behavior
– Concordance reflects 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
© 1999 John Wiley and Sons, Inc.
Age-Related Changes in
Concordance for MZ and DZ Twins
(Figure adapted by permission from “The Louisville Twin Study: Developmental Synchronies
in Behavior” by R.S. Wilson, 1983, Child Development, 34, p. 301. Copyright © 1983 by the
Society for Research in Child Development).
© 1999 John Wiley and Sons, Inc.
Vasta, 3e Fig. 4.9
Copyright
Copyright 1999 by John Wiley and Sons, New York, NY.
All rights reserved. No part of the material protected
by this copyright may be reproduced or utilized in any
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