Chapter 3
Biology and Behavior
Nature and Nurture
•Each of us is a product of our genetics and the
environment
•Historical views of how characteristics are
transmitted
 Galton (1869)
 Mendel
 Watson and Crick (1953)
 Currently scientists are attempting to figure out the
function of the roughtly 30,000 to 60,000 genes that
make up the human genome
Divisions of the Cell
• 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)
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)
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
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
– Genotype
– Principle of dominance
Mendelian Inheritance
Genetic Disorders
• Dominant disorders:
– Huntington’s chorea
• Recessive disorders:
– Phenylketonuria (PKU)
© 1999 John Wiley and Sons, Inc.
Genetic and Environmental Forces
•Model Components:
Genotype
Phenotype
Environment
•4 relations fundamental to a child’s development
Parents’ genotype
Child’s genotype
Child’s environment
Child’s phenotype
Child’s genotype
Child’s phenotype
Child’s phenotype
Child’s environment
Parents’ Genotype
•Terms:
 Chromosomes
 DNA
 Genes
 Proteins
Child’s Genotype
Diversity
Mutations—
Crossing over
•Chromosomes
 Sex Determination by Sex Chromosomes
Females XX
Males XY—presence of the Y chromosome determines male sex
Child’s Genotype
Child’s Phenotype
•Gene Expression
 Regulator genes control other genes (puberty, graying hair)
•Dominance Patterns
 Inheritance patterns are complicated with few following
Mendel’s simple pattern
 Alleles
 Dominance/Recessive genes
 Homozygous/Heterozygous
Mendelian
inheritance
patterns
Above are the Mendelian inheritance patterns for two brown-haired parents who are both
heterozygous for hair color. The allele for brown hair (B) is dominant, and that for blond
hair (b) is recessive. Note that these parents have three chances out of four of producing
children with brown hair. They have two chances in four of producing brown-haired
children who carry the gene for blond hair.
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 Transmission of Diseases and Disorders
 Dominant–Recessive Pattern—
2 recessive alleles (PKU, sickle-cell anemia, Tay-Sachs)
Dominant gene (Huntington’s disease)
 Polygenic Inheritance—combination of multiple genes and
environment (ADHD, some cancers, schizophrenia)
 Sex-Linked Inheritance
X-linked Disorders are more prevalent in men (hemophilia,
color-blindness, male-pattern baldness)
 Chromosomal Anomalies—more or less than the normal
complement of chromosomes (Down syndrome, Kleinfelter
syndrome, Turner syndrome)
 Regulator Gene Defects—which initiate the development of
genitalia
Child’s Environment
Child’s Phenotype
•Depending on the environment–genotype
relationship numerous phenotypes may result
 PKU—special diet
 Parents’ role—highly literate parents may have more books in
the home, exposing children to more literature
Child’s Phenotype
Child’s Environment
•For example, the activity level of a child gets
differing responses from adults
•Children create environments of interest, talents,
and personality
Behavioral Genetics
•The study of how variation results from
environmental factors and genetic
 Research Designs
Family studies
Twin studies
Adoption studies
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).
•Heritability
 A statistical estimate of the proportion of the measured variance
on a given trait among individuals in a given population that is
attributable to genetic differences among
the individuals
 For example IQ, temperament, and divorce
 Important restrictions:
Heritability applies only to populations, not to individuals
Heritability estimates apply only to a particular group
living in a particular environment at a particular time
High heritability does not imply immutability
Heritability estimates tell us nothing about difference
between groups
Experience and the Brain
•Plasticity
Experience-expectant plasticity
Sensitive periods
Experience-dependent plasticity
•Plasticity, Brain Damage, and Recovery
Recovery depends on
Extent of the damage
Aspect of the brain developing at time of damage
Damage may not be immediate
“Worst time” is during prenatal development
“Best time” is childhood during synapse generation
and pruning
Body Growth and Development
• Depends on nature and nurture, genetics, and the
environment
• Nutritional Behavior
 Breast feeding
 Food preference
 Eating disorders
Obesity
Bulimia
Anorexia Nervosa
 Undernutrition
Marasmus (low calories)
Kwashiorkor (low protein)
• Research has shown links between cognitive
development/performance and nutrition
Malnutrition and cognitive development
Malnutrition, combined with poverty, affects many aspects of development and can lead
to impaired cognitive abilities. (From Brown & Pollitt, 1996.)