Chapter 1 A Close-Up View of You 15
gene carrying the condition and a dominant
gene carrying a healthy trait. When both parents
are carriers, their children have one chance in four
of inheriting that disorder.
Each person is likely to carry some defective
genes, but no problems result in most cases because
the dominant genes are healthy. The defective genes
affect a person only when they are combined with
defective genes from both parents. This is why
marriage between blood relatives is discouraged.
Children of these marriages have a higher chance
of inheriting pairs of defective genes that may
result in disabilities at birth or even in death.
Genes are also a major factor in some
intellectual disabilities in children (Figure 1.10).
Down syndrome is a chromosome disorder that
occurs mostly in children born to women over 40
years old. As women age, their DNA molecules may
be altered in some way. Altered DNA passed on
to a child may result in the disorder occurring in
that child.
Hereditary Health Conditions
Certain diseases and disorders are genetic,
meaning they are inherited. With advances in
medicine, scientists can study a person’s genetic
makeup to identify the presence of these genes.
Scientists can take a sample of someone’s DNA
and compare it to DNA from people with various
diseases. For instance, scientists know that some
conditions result from a change in the sequence of
genes on a chromosome.
Some people are carriers of a disease or
disorder. This means they can pass the condition
to their children, but never have it themselves. This
situation occurs because they have one recessive
Give examples of how brain development could
impact your view of yourself.
A Hereditary Disease
Linda is a sophomore in high school and has
already lived longer than most people with her
condition. She has cystic fibrosis. Her parents do
not have the disease, nor do her brother or sister,
however, the disease is hereditary.
Linda appears healthy to those who meet her,
but she does not have much longer to live. Every day
she undergoes therapy to thin the mucus that affects
her breathing and digestion.
Her family members help her with the daily
treatments. They have grown very close to one
another, realizing that Linda’s life will be short. They
have also tried to help her live a normal life. She
does very well in school and has won honors for her
achievements.
The constant stress caused by Linda’s
condition affects her family. Frequent visits to the
hospital strain family finances. The daily therapy
routines take time and energy. Family members also
feel the emotional strain of not knowing how long
Linda will live.
For Discussion
1. Who in Linda’s family are carriers of cystic
fibrosis? Using D for a dominant healthy gene
and d for a gene for cystic fibrosis, identify a
genotype for both her mother and her father.
2. What are the chances th at each child in this
family would have cystic fibrosis? What are
the chances that Linda’s brother and sister are
carriers of cystic fibrosis? (Use a Punnett square
to diagram the answer.)
3. Why might Linda’s siblings seek genetic
counseling before getting married and starting
their own families?
4. Linda’s family environment has been affected by
her disease. Because of Linda’s disease, in what
areas might the growth of other family members
be slowed? In what areas might their personal
growth be enhanced?
5. Citing evidence from the text, explain how Linda’s
disease could impact her success in completing
the developmental tasks of adolescence.
Real-Life Scenario
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