H–K
Human Genome Project A collaborative under-
taking among researchers around the world,
organized under the joint auspices of the U.S.
Department of Energy and the National Institutes
of Health, to identify and map the human GENOME
(genetic material that defines the human being).
Altogether, more than 20 research centers in the
United States, United Kingdom, China, France,
Germany, and Japan participated in the DNA
sequencing. The Human Genome Project began in
1990 and concluded with the full mapping of
the human genome in April 2003, 50 years after
Watson and Crick unveiled their double-helix
model of DNA. Researchers expect data analysis
and new findings to continue for the indefinite
future. The Human Genome Project’s Web site,
(www.ornl.gov), regularly posts updates.
HUMAN GENOME PROJECT FINDINGS: HIGHLIGHTS- The human GENOMEconsists of 3,164,700,000 NUCLEOTIDE
bases. - The largest GENE(dystrophin) contains 2.4 million nucleotide
bases. - 99.9 percent of the nucleotide bases are identical in all peo-
ple. - The human genome contains about 30,000 genes.
- CHROMOSOME1 contains 2,968 genes and chromosome Y
contains 231 genes, the most and the fewest, respectively.
Source:The Science behind the Human Genome Project,
http://www.ornl.gov/hgmis; updated October 27, 2004.
See also CELL STRUCTURE AND FUNCTION; CLONING;
ETHICAL ISSUES IN GENETICS AND MOLECULAR MEDICINE;
GENOTYPE; PHENOTYPE; RECOMBINANT DNA.
inheritance patterns The ways in which geno-
types pass among individuals and generations.
Many inherited traits are either autosomal or X-
linked and either dominant or recessive. Such
inheritance patterns reflect statistical calculations
assessing the mathematical likelihood of certain
traits or mutations passing from one generation to
the next. Inheritance patterns consider the geno-
types of each parent. Inheritance patterns vary
according to whether the chromosomes responsi-
ble are autosomesal or sex-linked chromosomes.
Geneticists often refer to these patterns as
Mendelian, in reference to the foundational work
of botanist Gregor Mendel (1822–1884), who was
the first to delineate inheritance patterns.
Recent research, notably through the HUMAN
GENOMEPROJECT, has shown that much of human
inheritance may not be quite so simple as the
Mendelian model. Multiple genes and chromo-
somes share responsibility for traits ranging from
EYEcolor to the development of diseases, such as
DIABETES AND CARDIOVASCULAR DISEASE, that also
have environmental (lifestyle) components. This
circumstance of multiple factors makes it far more
difficult to statistically represent a delineated pat-
tern of inheritance. Multifactorial inheritance is
not clearly dominant or recessive, though is com-
monly autosomal (derives from autosomes rather
than sex chromosomes).
The least common pattern of inheritance is
mitochondrial, which comes only from the
mother and involves traits and mutations affecting
mitochondrial, not nuclear, DNA. This pattern is
exclusively maternal because only the ovum
(female GAMETE or egg) contains mitochondria.
Mitochondria affect functions rather than struc-
tures of the body, and thus, mitochondrial muta-
tions cause numerous, nonspecific multisystem
disturbances. Because mitochondria are the
energy generators of the cells, mitochondrial
mutations affect functions that require energy132