This section, “Genetics and Molecular Medicine,”
presents an overview discussion of the structures
and functions of human genetics and entries
about genetic health and disorders. The entries in
this section focus on genetic consequences for
health across the spectrum of the body as a
whole, including disorders and diseases that affect
multiple systems. Entries in other sections of The
Facts On File Encyclopedia of Health and Medicinepro-
vide detailed content about conditions that result
from genetic disorders that affect single body sys-
tems. Cross-references connect entries with one
another.
Structures of Genetics
GENE/ALLELE cell
CHROMOSOME nucleus
DNA cytoplasm
RNA ribosome
mitochondrion
molecule
Functions of Genetics
Genetics determines every aspect of human exis-
tence, from appearance and structure to function.
Each individual acquires one set of chromosomes,
the molecular presentation of heredity, from each
parent. Each complete complement of chromo-
somes (23 pairs) contains 25,000 to 30,000 genes,
the smallest structural and functional units of
heredity. Each GENEpair within the structure of a
CHROMOSOME has a single and specific task. It
accomplishes this task by instructing the cell to
make a particular protein, a process called protein
encoding. Through protein encoding genes direct
every action of every cell.
The genome: the book of lifeThe complete com-
plement of chromosomes is the human GENOME,
quite literally the book of life. The genome contains
all of the instructions the body requires to take
shape and to function. Within a single individual,
every one of the body’s 100 trillion cells contains
the same set of chromosomes, so all cells in the
body read from the same book of life.
DNA(deoxyribonucleic acid) is the ink of the
genome, the biochemical substance that allows
the GENETIC CODEto express itself. DNA organizes
itself in chemical presentations called nucleotides,
which function somewhat like letters. Human
DNA presents a surprisingly brief alphabet for the
extensive range of genetic expression it permits,
forming only four NUCLEOTIDE compounds that
subsequently shape the 30,000 or so genes the
human genome contains. One of the most intrigu-
ing discoveries of the HUMANGENOMEPROJECTis
that there are vast amounts of “empty” DNA.
Only 1 to 2 percent of DNA encodes. The remain-
ing 98 to 99 percent of DNA is noncoding, much
like white space on the printed page of a book.
Researchers believe noncoding DNA somehow
stabilizes or in other ways supports the structure
of DNA within the chromosomes.GENETICS AND
MOLECULAR MEDICINE
Genetics and molecular medicine are the disciplines in health care that focus on genetic encoding and molecular func-
tion within the cell as the foundations for health and disease. Many medical researchers believe nearly every compo-
nent of health—and correspondingly, every presentation of disease—has some degree of genetic involvement and an
individual acquires whatever propensity toward health that his or her genes convey. The manifestations of health and
disease in many situations then become a combination of genetics and environment (lifestyle factors). The specialists
who diagnose and treat GENETIC DISORDERSare geneticists.
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