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The number of chromosomes in a sperm or egg cell, half the diploid number.
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A situation in which the protein produced by a single copy of an otherwise normal gene is not sufficient to assure normal function.
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An unspecialized precursor cell that will develop into a mature blood cell.
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A sex-linked inherited bleeding disorder that generally only affects males. The disorder is characterized by a tendency to bleed spontaneously or at the slightest injury because of the lack of certain clotting factors in the blood.
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Possessing two different forms of a particular gene, one inherited from each parent.
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A DNA sequence that is very similar in several different kinds of organisms. Scientists regard these cross species similarities as evidence that a specific gene performs some basic function essential to many forms of life and that evolution has therefore conserved its structure by permitting few mutations to accumulate in it.
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A congenital disorder in which part of the colon lacks nerve cells and therefore is unable to relax. The result is chronic constipation and distention of the abdomen. The disorder affects about one in 5000 U.S. newborns but can be treated with surgery.
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A birth defect where the forebrain does not separate properly into two halves during early fetal life. The disorder results in mild to severe brain malformation and is sometimes fatal. It may be caused by environmental or genetic factors. Holoprosencephaly affects between 1 in 5,000 and 1 in 10,000 live births.
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The exchange of pieces of DNA during the formation of eggs and sperm. Recombination allows the chromosomes to shuffle their genetic material, increasing the potential of genetic diversity. Homologous recombination is also known as crossing over.
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Possessing two identical forms of a particular gene, one inherited from each parent.
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(HAC) A vector used to transfer or express large fragments of human DNA. HACs behave and are constructed like human chromosomes.
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An international research project to map each human gene and to completely sequence human DNA.
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(HIV) OR acquired immunodeficiency syndrome (AIDS). AIDS was first reported in 1981 in the United States and has since become a major epidemic, killing nearly 12 million people and infecting more than 30 million others worldwide. The disease is caused by HIV, a virus that destroys the body's ability to fight infections and certain cancers.
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A degenerative brain disorder that usually appears in mid-life. Its symptoms, which include involuntary movement of the face and limbs, mood swings, and forgetfulness, get worse as the disease progresses. It is generally fatal within 20 years.
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Base pairing of two single strands of DNA or RNA.
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