Encyclopedia of Health and Medicine

110 Genetics and Molecular Medicine
Each gene, like a word, contains patterns of
nucleotides. Chromosomes, like sentences and
paragraphs, present strings of genes that convey
integrated and coordinated sets of instructions for
specific structures and functions throughout the
body. Collectively these genetic instructions are
the pages, written in code, that form an individual’s
GENOTYPE. The outcome, the individual’s outward
presentation of his or her genetic code from
appearance to health, is the PHENOTYPE.
Decoding the messages: the cells The cells
decode, interpret, and implement an individual’s
genotype. Each gene carries an encoded message
that it transcribes to RNA (ribonucleic acid), a carrier
molecule within the cell. The RNA conveys the
gene’s message to the cell’s ribosomes. Ribosomes
are organelles (defined structures with specific
functions) within the cell. The job of the ribosome
is to translate the gene’s message into a specific protein.
The protein then carries the message to its target
within the body, which is usually molecular.
Transmitting the code: inheritance patterns
The function of conveying a genotype is as much
one of mathematics as biology. INHERITANCE PAT-
TERNS—the ways in which genes reorganize into
new pairs at CONCEPTION—are the patterns of statistics.
A geneticist can calculate with astonishing
accuracy the likelihood of certain traits passing
from parents to offspring. Such calculations
accommodate the potential combinations that can
arise from each parent’s genotype.
Health and Disorders of Genetics
In some respects what is perhaps most remarkable
about human genetics is the precision and consistency
with which myriad, intricate, and complex
biochemical actions take place not only to produce
a new human being but also to choreograph its
functions for eight decades or longer. Though
everyone’s genotype contains some mutations,
researchers believe most mutations have no consequence
for the body’s structure or function.
However, understanding of the complex interactions
among genes continues to evolve as geneticists
engage in further research.
It is a common misperception that there are
genes that cause disease, such that there are specific
genes for HEMOPHILIA or CYSTIC FIBROSIS in the
same fashion as there are certain genes for brown
HAIR or green eyes. There are not really “disease”
genes, however. There are instead flaws and errors
in the structures of certain genes (mutations) that
cause them to give the wrong instructions for synthesizing
their specific proteins. The consequence
is a gap, expansion, or rearrangement in the information.
In some situations a gene, or more commonly
a segment of or an entire chromosome, is
missing—as if pages or chapters are torn from the
genetic book of life. In other situations the gene
may have extra material or its material is
rearranged—as if pages or chapters are inserted
into the book. The resulting errors in structure or
function can be quite significant.
IDENTIFIED GENETIC AND MOLECULAR DISORDERS
ALPORT SYNDROME
CONGENITAL HEART DISEASE
CYSTIC FIBROSIS
EDWARDS SYNDROME
FAMILIAL ADENOMATOUS
POLYPOSIS (FAP)
FRAGILE X SYNDROME
HEMOCHROMATOSIS
HEREDITARY NONPOLYPOSIS
COLORECTAL CANCER (HNPCC)
KERATOCONUS
KLINEFELTER’S SYNDROME
MARFAN SYNDROME
MYOPATHY
NEURAL TUBE DEFECTS
PHENYLKETONURIA (PKU)
PORPHYRIA
RETINOBLASTOMA
SYNDACTYLY
THALASSEMIA
TURNER’S SYNDROME
WILSON’S DISEASE
WOLFF-PARKINSON-WHITE
SYNDROME
CLEFT PALATE/CLEFT PALATE AND
LIP
DOWN SYNDROME
EPIDERMOLYSIS BULLOSA
FAMILIAL MEDITERRANEAN FEVER
FANCONI’S SYNDROME
G6PD DEFICIENCY
HEMOPHILIA
HUNTINGTON’S DISEASE
hypertrophic
CARDIOMYOPATHY
LONG QT SYNDROME (LQTS)
MUSCULAR DYSTROPHY
myotonia congenita
PATAU SYNDROME
POLYDACTYLY
PROGERIA
SICKLE CELL DISEASE
TAY-SACHS DISEASE
TRIPLE X SYNDROME
VACTERL
VON WILLEBRAND’S DISEASE
Researchers have identified more than 6,000
monogenic (single gene) mutations that result in
health disorders, affecting 1 child in every 200
born. Among them are CYSTIC FIBROSIS, SICKLE CELL
DISEASE, MARFAN SYNDROME, HUNTINGTON’S DISEASE,
and HEMOCHROMATOSIS. Other disorders, such as
CLEFT PALATE/CLEFT PALATE AND LIP, result from polygenic
(multiple gene) mutations or CHROMOSOMAL