The Developing Person Through Childhood and Adolescence
by Kathleen Stassen Berger
Seventh Edition
Chapter 3
Heredity and
Environment
Slides prepared by Kate Byerwalter, Ph.D.,
Grand Rapids Community College
The Genetic Code

Chromosomes: a molecule of DNA that
contains the instructions to make proteins

The instructions are organized into genes,
the basic unit for transmitting heredity.

Humans have 46 chromosomes (23 pairs),
and about 25,000 genes.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Karyotype (Map of Chromosomes)
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
The Genetic Code (cont.)

Human genome: the code for making a
human being

Every person has a slightly different code,
but the human genome is 99.5% the same
for any 2 people.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
The Beginnings of Life

Development begins at conception, when
the sperm penetrates the ovum.

The organism is first called a zygote, and
is the fused nuclei of sperm and egg.

The genotype of the zygote is the genetic
information on the 23 chromosome pairs.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Gene Pairs

Gene pairs are closely matched on 22 of
the 23 chromosomes.

In some cases, an allele occurs: an
alternate version of variable genes.

On the 23rd pair, XX = female, XY = male.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Determining a Zygote’s Sex
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
From One Cell to Many

The phenotype is the actual appearance
and behavior of a person, and occurs
because some instructions on the
genotype are ignored, and others
amplified.

This occurs through cell differentiation,
gene-gene (polygenic), and geneenvironment interactions.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Human Genome Project

The Human Genome Project is an
international effort to map the entire
human genome.

It has already revealed a great deal about
the nature of genes and genetic variations.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Additive Heredity

Additive genes combine to make a
phenotype.
 Example:
HEIGHT. The inherited genes from
mother and from father are added together.
However, some additive genes get enhanced
by other genes, making their input greater.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Dominant-Recessive Heredity

A dominant-recessive pattern occurs
when the influence of one gene in the
allele is greater than the other gene.
 Example:
Blood types A and B and brown
eyes result from dominant genes.

This pattern may be X-linked (on the X
chromosome), in which case males are
more affected (e.g., color-blindness).
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Twins and Clones

Dizygotic (fraternal) twins result from
two sperm penetrating two ova, and share
50% of their genes.

Monozygotic (identical) twins originate
from one zygote, and share 100% genes.

A clone originates from a live organism.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Dizygotic or monozygotic?
DAVID YOUNG-WOLFF / PHOTOEDIT
BRUCE ROBERTS / PHOTO RESEARCHERS, INC.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Multiple Births

The likelihood of multiple births vary by
age and ethnicity. Fertility treatments
may also cause them.

Hazards of multiples include birth
complications, death, disease, and
disabilities.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Research on the Effects of Genes

Researchers have employed several
methods (e.g., twin studies, adoption
studies) to investigate the relative
influence and interaction of genes and
environment in shaping human behavior
and traits.

The results may surprise you!
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Findings from Genetic Research

Genes affect every aspect of human
behavior.

The non-shared environment of families is
powerful.

Genes elicit responses from other people
that shape development (an indirect
effect).
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Psychopathology

Genes have been found to influence
several disorders, including:
 Schizophrenia
 Addiction
 Nearsightedness
 Diabetes

However, the environment ALSO plays a
key role in these disorders.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Chromosomal Abnormalities

Chromosomal abnormalities when the
zygote’s cells have fewer or more
chromosomes than 46.

Maternal age is the most common
correlate of chromosomal abnormalities.

Many zygotes with chromosomal
abnormalities are spontaneously aborted.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Down Syndrome (Trisomy 21)

Down syndrome occurs when a zygote
has 3 copies of chromosome 21.

Sufferers experience mental slowness,
faster aging, and physical problems.

Social support and a positive attitude help.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Abnormalities of the 23rd pair

About 1 in 500 infants have either one too
many or too few chromosomes on the
23rd pair.

This can lead to underdeveloped sexual
organs (girls), breast development (boys),
or other anomalies.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Dominant Disorders

Huntington’s disease is a fatal CNS
disorder caused by a genetic miscode. It is
inactive until middle adulthood.

Tourette syndrome, a dominant disorder,
can lead to uncontrollable tics and
obscenities.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Fragile X Syndrome

Fragile X syndrome is caused by a single
gene that has 200 repetitions of a triplet.

The effects of Fragile X include cognitive
deficits and poor social skills.

Males are at greater risk of developing this
syndrome.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Genetic Counseling

Genetic counseling provides facts. It is
recommended for:
 Couples
from the same ethnic group
 Individuals with a close relative with a genetic
condition
 Couples with a history of infertility or miscarriage
 Women 35 or older, men 40 or older
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Genetic Counseling (cont.)

Genetic counseling raises a number of
ethical and complicated issues.
 Example:
What if a couple decides to abort a
child of abnormal height?

Results are an estimate of risk, not a
guarantee that a disorder will or won’t
occur.
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3
Genetic
Counseling
Decision
Tree for
High-Risk
Couples
Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3