HUMAN BIOLOGY

DNa, GeNes, aND BioteChNoloGy 417

DNA chip A glass plate

containing a microscopic

array of DNA sequences.

What has the humaN geNome project

accomplisheD?

• The Human Genome Project has determined the sequence of
  nucleotides in the human genome.


• The project is now mapping the locations of specific genes on
  chromosomes.


• Already, information gleaned from human genome mapping is
  being used to help diagnose diseases and develop more
  effective treatments.

taKe-home messaGe

inborn predisposition to heart dis-

ease, asthma, diabetes, and certain

cancers. Armed with your profile,

your doctor might be able to diag-

nose and treat problems earlier and

more effectively. Drugs may be customized for various

genetic situations, as described in Section 20.7. This sort of

personalized medicine is rapidly becoming a reality.

Along with the promise of genome sequencing come

serious cautions. Many people worry that genetic profil-

ing could lead to discrimination against people seeking

employment or insurance, based solely on their genetic

makeup. New issues could arise in the genetic screening of

embryos, already a major ethical concern to some. Clearly,

a challenging genetic future awaits us.

amyotrophic lateral sclerosis, or ALS, a disease that
destroys motor neurons (Figure 21.17). More than sixty
disorders have been mapped to chromosome 14. Currently,
efforts are underway to figure out how individual genetic
differences may correlate with genetic disorders. Appendix
VII at the end of this book shows maps for all 23 human
chromosomes and provides information you can use to
research human genetic diseases on your own.

Dna chips help identify mutations
and diagnose diseases

One key tool is the DNA chip, a microscopic array (micro-
array) of thousands of DNA sequences that are stamped
onto a small glass plate (Figure 21.18). The chips can
quickly pinpoint which genes are being expressed in a
tissue, including tissues such as cancerous tumors. DNA
chips, including so-called SNP-chips, are now being used
to locate mutations, diagnose genetic diseases, and test how
drugs or other therapies affect the functioning of genes.
As new genes are identified, biologists are exploring
the roles of proteins they encode. We already know how
having a particular allele can set the course of diseases
such as sickle-cell anemia and forms of breast cancer.
SNP-chips now are used to test patients for genetic muta-
tions associated with increased breast cancer risk, among
other conditions. Soon it will be possible to apply the
deeper understanding of human genes to many more
health concerns. For instance, a simple blood test might
be able to provide a complete genetic profile of a person’s

F i g u r e 21.17 A map of human chromosome 21 shows genes
correlated with several diseases. The upper arm of the chromosome
is marked p and the lower arm q. In this case, each arm has a single
region, labeled 1 and 2, respectively. In other chromosomes, each
arm may have two or more regions. Stains used in chromosome
analysis produce a series of bands, indicated by the small numbers to
the left of each arm. A combination of letters and numbers indicates
the chromosome region where a given gene is found; for instance, the
gene for one form of amyotrophic lateral sclerosis (ALS) is 21q2.22.
A total of 225 genes have been mapped to this chromosome.
(© Cengage Learning)

F i g u r e 21.18 DNA chips can be used to analyze thousands

of genes at once. This researcher is studying a microarray

that reveals SNPs. The analysis of SNPs is useful in screening

individuals for mutations associated with increased risk of

certain diseases. (Science Source)

11

12

21

22

2

1

Amyloidosis, cerebroarterial, Dutch type

Alzheimer’s disease, one form

Schizophrenia, chronic, one form

Amyotrophic lateral sclerosis, one form

Down syndrome (critical region)

Epilepsy, progressive myoclonus

Hemolytic anemia due to

phosphofructokinase deficiency

Leukemia, acute myeloid

Leukocyte adhesion deficiency

Homocystinuria, B 6 -responsive and

B 6 -unresponsive

q

p

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