Encyclopedia of Health and Medicine

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gamete A spermatozoon (SPERM cell) or an ovum
(egg cell). A gamete, also called a germ cell or sex
cell, is a haploid cell; it contains half the complement
of chromosomes and genetic material necessary
to encode (result in creating) an individual.
When two gametes merge they produce a single
diploid cell, the ZYGOTE, which then contains the
full complement of chromosomes needed for life.
For further discussion of gametes within the
context of the structures and functions of genetics,
please see the overview section “Genetics and
Molecular Medicine.”
See also CELL STRUCTURE AND FUNCTION; CHROMO-
SOME; CONCEPTION; OVULATION.
gene A segment of coding DNA (DNA that
instructs the structure and function of cells
throughout the body) composed of a specific
sequence of nucleotides. The gene is the basic unit
of inheritance that directs every facet of the body’s
appearance and functions. Genes align along chromosomes
in pairs. Each CHROMOSOME (AUTOSOME)
contains thousands of genes, except the sex chromosomes
which contain only a few hundred
genes.
Each gene has a specific location on the chromosome,
called its locus, and encodes a specific
function (either a protein or RNA transcription).
The HUMAN GENOME PROJECT identified 19,599 confirmed
genes and 2,188 probable genes at its conclusion
in April 2003. GENETIC DISORDERS occur
when there are disruptions of the ALLELE pairings
or there is damage to the gene or the chromosome
at or near the gene’s locus.
Each gene has a specific task, which it carries
out through a process called encoding. The gene
instructs the cells to synthesize (produce) a specific
protein. Ribosomes, specialized structures
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within each cell, synthesize the proteins. The protein
then carries the gene’s message to its target
and initiates the appropriate sequence of biochemical
events to implement the message.
For further discussion of genes within the context
of the structures and functions of genetics,
please see the overview section “Genetics and
Molecular Medicine.”
See also CHROMOSOMAL DISORDERS; GENOME;
INHERITANCE PATTERNS; MUTATION; NUCLEOTIDE; SEX
CHROMOSOME.
gene therapy Treatment methods, most of
which remain experimental, that attempt to
manipulate genetic structure or gene encoding.
GENE therapy targets either germline (GAMETE) or
somatic cells, using vectors to deliver genes within
cells. Germline gene therapy aims to prevent a
genetic disorder from passing to new generations,
while somatic gene therapy targets genetic
disorders that already exist in individuals. Most
often the goal of gene therapy is to replace a
defective gene with a healthy, functional gene.
The vectors typically used are inactivated viruses
into which scientists insert the replacement gene.
The VIRUS enters the target cell and delivers the
gene.
Applications of gene therapy have not been as
successful as researchers have hoped was possible,
however, and at present the US Food and Drug
Administration (FDA) has not approved any gene
therapy methods for use in the United States. The
effects of gene therapy appear time-limited, and
viral vectors often initiate immune responses.
Researchers continue to investigate safe and effective
mechanisms to therapeutically manipulate
genes with the goal of treating or curing GENETIC
DISORDERS.