Section 1:2 Heredity
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Hereditary Diseases
Certain diseases and disabilities are inherited.
With advances in medicine, there are new ways to
identify these disease traits. Scientists can take a
sample of your DNA and identify your particular
gene traits. The genotypes of healthy people
are compared to those with various diseases.
For instance, scientists know that some diseases
result from a change in the sequence of genes
on a chromosome. This information should help
identify causes of and cures for many diseases.
Some people are a carrier of a disease. This
means they can pass the disease to their children
but never have it themselves. This situation
occurs because they have one recessive gene
carrying the disease trait and a dominant gene
carrying a healthy trait. When both parents are
carriers, their children have one chance in four of
inheriting that disease.
Heredity is also a major factor in mental
retardation in children, 1-8. 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 hereditary diseases.
Each person is likely to carry some defective
genes, but no problems result because the dominant
genes are healthy. Defective genes affect a person
when they are inherited in pairs. This is why
marriage between blood relatives is discouraged.
Children of these marriages have a higher chance
of inheriting pairs of defective genes, which may
result in birth defects and even death.
Cell body
Myelin
sheath
Axon
Synapse
Dendrites
Cell body
1-7
A nerve cell, or neuron, can send 250 to 2500 nerve
impulses each second.
Although your heredity determines the
number of brain cells you start with, your
environment affects the number of connections
made. Good nutrition is important for brain
development. A stimulating environment is just
as important. To reach your full potential, all
these factors need to come together. (You will
learn more about the parts of the brain and how
to stimulate development in Chapter 2.)
Give examples of the use-it-or-lose-it
rule. Include activities that improve with
practice.
Use What You Learn
How might researchers and doctors
use DNA information to help identify
causes of and cures for hereditary
diseases?
Investigate Further