Genetics Vocabulary

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Achondroplasia

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the most common and well known form of short limbed dwarfism characterized by a normal trunk size with disproportionally short arms and legs, and a disproportionally large head; autosomal dominant condition.

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Advanced maternal age

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women over age 34 (age 35 at delivery) at increased risk for nondisjunction trisomy in fetus.

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Alcoholism

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a chronic and progressive condition characterized by the inability to control the consumption of alcohol.

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Allele

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an alternative form of a gene; any one of several mutational forms of a gene.

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Alpha-fetoprotein (AFP)

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a protein excreted by the fetus into the amniotic fluid and from there into the mother's bloodstream through the placenta

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Alu repetitive sequence

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the most common dispersed repeated DNA sequence in the human genome accounting for 5% of human DNA. The name is derived from the fact that these sequences are cleaved by the restriction endonuclease Alu.

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Amino acid sequence

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the linear order of the amino acids in a protein or peptide.

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Amniocentesis

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prenatal diagnosis method using cells in the amniotic fluid to determine the number and kind of chromosomes of the fetus and, when indicated, perform biochemical studies

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Amniocyte

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cells obtained by amniocentesis

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Amplification

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any process by which specific DNA sequences are replicated disproportionately greater than their representation in the parent molecules.

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Aneuploidy

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state of having variant chromosome number (too many or too few). (i.e. Down syndrome, Turner syndrome).

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Angelman syndrome

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a condition characterized by severe mental deficiency, developmental delay and growth deficiency, puppet-like gait and frequent laughter unconnected to emotions of happiness.

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Apert syndrome

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a condition caused by the premature closure of the sutures of the skull bones, resulting in an altered head shape, with webbed fingers and toes. Autosomal dominant.

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Artificial insemination

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-- the placement of sperm into a female reproductive tract or the mixing of male and female gametes by other than natural means

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Autosome

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a nuclear chromosome other than the X- and Y-chromosomes.

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Autoradiograph

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a photographic picture showing the position of radioactive substances in tissues.

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Bacteriophage

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a virus whose host is a bacterium; commonly called phage

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Barr body

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the condensed single X-chromosome seen in the nuclei of somatic cells of female mammals.

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Base sequence

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a partnership of organic bases found in DNA and RNA; adenine forms a base pair with thymine (or uracil) and guanine with cytosine in a double-stranded nucleic acid molecule.

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Baysian analysis

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a mathematical method to further refine recurrence risk taking into account other known factors.

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Becker muscular dystrophy

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X-linked condition characterized by progressive muscle weakness and wasting; manifests later in life with progression less severe than Duchenne muscular dystrophy.

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Carrier

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an individual heterozygous for a single recessive gene.

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cDNA

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complementary DNA produced from a RNA template by the action of RNA- dependent DNA polymerase.

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Centromere

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a region of a chromosome to which spindle traction fibers attach during mitosis and meiosis; the position of the centromere determines whether the chromosome is considered an acrocentric, metacentric or telomeric chromosome.

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Charcot-Marie Tooth disease

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a condition characterized by degeneration of the motor and sensory nerves that control movement and feeling in the arm below the elbow and the leg below the knee; transmitted in autosomal dominant, autosomal recessive and X-linked forms.

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Chorionic villus sampling

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an invasive prenatal diagnostic procedure involving removal of villi from the human chorion to obtain chromosomes and cell products for diagnosis of disorders in the human embryo.

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Chromosome

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in the eukaryotic nucleus, one of the threadlike structures consisting of chromatin and carry genetic information arranged in a linear sequence

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Chromatid

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Either of the two daughter strands of a replicated chromosome that are joined by a single centromere and separate during cell division.

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Chromosome banding

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a technique for staining chromosomes so that bands appear in a unique pattern particular to the chromosome.

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Cleft lip/palate

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congenital condition with cleft lip alone, or with cleft palate; cause is thought to be multifactorial.

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Clone

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genetically engineered replicas of DNA sequences

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Cloned DNA

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any DNA fragment that passively replicates in the host organism after it has been joined to a cloning vector.

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Consanguinity

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-- genetic relationship. Consanguineous individuals have at least one common ancestor in the preceding few generations.

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Conservative change

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an amino acid change that does not affect significantly the function of the protein.

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Cosmids

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plasmid vectors designed for cloning large fragments of eukaryotic DNA; the vector is a plasmid into which phage lambda cohesive end sites have been inserted.