Chapter 4
How Children Develop
Nature through Nurture
 The Study of Genetics and Behavior
 The Interaction of Genes and Environment
 The Study of Culture and Behavior
The Study of Genetics and Behavior
 How We Study Genes and Behavior
 How Do Genes Work?
 Genetic Disorders
Nature versus Nurture?
Nature through Nurture!
 Throughout history the idea of whether our
lives are determined by our genes or by the
environment has shifted from one extreme
to the other.
 D. O. Hebb: asking whether behavior is due
to nature or to nurture is similar to asking
whether the area of a rectangle is due to its
length or its width (Meaney, 2004).
 Genetic and environmental influences are
entangled in complex ways.
How We Study Genes and Behavior
 Molecular genetics: Identification of
particular genes to discover how these
genes work within the cell.
 Behavioral genetics: Determining the
degree of genetic basis for a behavior, a
trait, or an ability through studies of twins
and adopted children
Behavioral Genomics
Behavioral genomics: Research that links
behaviors, traits or abilities with specific
genes.
The Human Genome Project
 The Human Genome Project mapped all the
genes that make up the human body
 http://www.youtube.com/watch?v=ubQsaoH
BxsU&feature=fvw
 25,000-30,000 genes determine everything
about our genetic inheritance.
 We know what only about half of these
genes actually do.
Results of the Human Genome
Project: Chromosome 12
Our Genetic Beginnings
 Egg and sperm unite to form a zygote.
 23 chromosomes from each pair up to form
23 pairs of chromosomes.
 22 are autosomes
rd
 The 23 is the pair that determines the sex:
XX or XY.
 The father’s sperm determines the sex of
the child by contributing either an X or a Y
chromosome
Female and Male Chromosomes
Chromosomes, Genes, DNA,
and Bases (GATC)
 Chromosomes are made up of
 Genes, which are made up of
 DNA, which is made up of
 4 nitrogenous bases:
 Guanine (G), adenine (A), thymine (T),
cytosine (C)
The order of the bases determines which
proteins are produced which make the body
develop and perform all its activities
Chromosomes
 Which combination produces a protein?
 How to divide the series:
ATCATCTTTGGTGTT
 How would you divide the following series of
letters?
 Gotothegrocerystorepickupmilkcomehome
Chromosomes must fit in certain
patterns to work effectively
NOT:
Got oth egro
ceryst orepick upm
ilk comeho me
BUT RATHER
Go to the grocery store. Pick up milk. Come
home.
Scientists must find the combinations in the
sequences that make sense.
Mendelian Inheritance: Dominant and
Recessive Genes
 Most genes are paired with a gene on the
matching chromosome.
 One of these 2 paired genes may be
dominant and one recessive.
 Your genotype contains all the genes in
your body.
 Your phenotype is which genes are
expressed in your body.
Genotype vs. phenotype
 Dominant genes will be expressed in your
phenotype.
 Recessive genes will only be expressed if
they are paired with another recessive
gene.
Recessive gene disorders
 Tay-Sachs disease
 Sickle-cell anemia
One gene: one outcome?
 The field vole and the mountain vole:
 One gene determines whether they mate for
life or “play the field”.
 Can this be true for human beings? What
else would be involved besides (or in
addition) to a particular gene?
Many genes: one outcome
One gene: many outcomes
 Polygenic inheritance: many genes interact
together to produce a particular trait or
behavior
Pleiotropic effects; Any single gene can
have many very different effects
Genetic disorders
 Single gene disorders
 Tay Sachs disease
 PKU
 Sickle cell anemia
 Cystic fibrosis
The problem with the Y-chromosome
 The Y-chromosome is small and carries few
genes.
 It pairs with an X-chromosome with lots of
genes.
 Any recessive genes on the X-chromosome
that do not have a partner on the Ychromosome will be expressed in the
phenotype.
Boys’ vulnerability
 Therefore, boys are more prone to genetic
disorders than girls.
 For example
 Color-blindness
 Hemophilia
 Duchenne muscular dystrophy
Genetic disorders
Chromosomal disorders:
 Down syndrome: one extra chromsome
#21
 Klinefelter syndrome: XXY
 Turner syndrome: XO
 Fragile X syndrome: One gene segment
(CGG) on the X chromosome is
repeated 200 times, rather than 5–40
times.
Genetic counseling and testing
 In each pregnancy, any couple statistically
has a 3% chance of having a child with a
genetically based disorder. Those at higher
risk may have genetic counseling and/or
testing:
 Family history of genetic disorders
 Blood tests for certain genes before
pregnancy
Prenatal testing
 During pregnancy:
 blood tests – alpha-feta protein test
 Amniocentesis
 Chorionic villus sampling (CVS)
Interaction of Genes and
Environment
 How the environment shapes gene
expression
 How genes shape the environmental
influences
How the environment shapes gene
expression
 Canalization: The degree to which the
expression of a gene is influenced by the
environment
 Epigenetics: A system by which genes are
activated or silenced in response to events
or circumstances in the individual’s
environment
Interaction of genes and the
experience of child abuse
How genes shape the environmental
influences
 Passive gene-environment interaction:
When a child’s family shares his own
genetically determined abilities and
interests.
 Active gene-environment interaction:
When one’s genetic endowment becomes a
driving force for children to seek out
experiences that fit their genetic
endowments.
Genes and environment are in a
complex dance
 Evocative gene-environment interaction:
When children’s genetic endowment causes
them to act in a way that draws out or
“evokes” certain responses from those
around them.
Study of the role of genes in
behavior: Behavioral genetics
 Studies of adopted children
 Concordance rate with biological
parents and adoptive parents
 Studies of identical (MZ) twins compared
with non-identical (DZ) twins
 Studies of identical twins reared apart
http://www.youtube.com/watch?v=REhKa3_
oHL8
The study of culture and behavior:
Environment effects
 Culture: behaviors, norms, beliefs, and
traditions that promote the survival of a
group in a particular environmental niche.
 It is a way of describing similarities
within one group of people and
differences between groups of people.
Difference versus deficit
 Deficit model: other cultures do not live up
to one’s own standards
 Difference model: other cultures must be
understood in their own context
Cultural values: Individualism and
collectivism
 Individualism The cultural value that
emphasizes the importance of the
individual with emphasis on independence
and reliance on one’s own abilities
 Collectivism: The cultural value that
emphasizes obligations to others within
your group
 http://www.youtube.com/watch?v=4uFa0h
BPqOY
What are your cultural values? Agree
or disagree:
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1. I tend to do my own thing, and others in my family
do the same.
2. To understand who I am, you must see me with
members of my group.
3. I take great pride in accomplishing what no one
else can accomplish.
4. To me, pleasure is spending time with others.
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5. It is important to me that I perform better than
others on a task.
6. I would help, within my means, if a relative were in
financial difficulty.
7. I am unique—different from others in many
respects.
8. I make an effort to avoid disagreements with my
group members.
9. I like my privacy.
10. How I behave depends on whom I am with, where
I am, or both.
11. I know my weaknesses and strengths.
12. I have respect for the authority figures with whom
I interact.
13. I always state my opinions very clearly.
14. I would rather do a group paper or lab than do one
alone.
Transmitting culture to children
American mothers promote independence
in feeding
 Puerto Rican mothers promote
interdependence in feeding
Conclusion
 Genes influence the environment
 The environment influences gene
expression
 The interaction is complex and research is
ongoing on this important topic.
 BUT
 We now know that we are not formed
entirely by our genes and we are not formed
entirely by our environment.