Achondroplasia -- 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.
Advanced maternal age -- women over age 34 (age 35 at delivery) at increased risk for nondisjunction trisomy in fetus.
Alcoholism -- a chronic and progressive condition
characterized by the inability to control the consumption of alcohol.
Allele -- an alternative form of a gene; any one of several mutational forms of a gene.
Alpha-fetoprotein (AFP) -- a protein excreted by the fetus into the amniotic fluid and from there into the mother's bloodstream through the placenta.
Alu repetitive sequence -- 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.
Amino acid sequence -- the linear order of the amino acids in a protein or peptide.
Barr body -- the condensed single X-chromosome seen in the nuclei of somatic cells of female mammals. base pair a pair of hydrogen-bonded nitrogenous bases (one purine and one pyrimidine) that join the component strands of the DNA double helix.
Base sequence -- 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.
Baysian analysis -- a mathematical method to further refine recurrence risk taking into account other known factors.
Becker muscular dystrophy -- X-linked condition characterized by progressive muscle weakness and wasting; manifests later in life with progression less severe than Duchenne muscular dystrophy.
individuals have at least one common ancestor in the preceding few generations.
Degenerate codon -- a codon that specifies the same amino acid as another codon.
Deletion -- the loss of a segment of the genetic material from a chromosome.
DNA hybridization -- a technique for selectively.
Linkage -- the greater association in inheritance of two or more nonallelic genes than is to be expected from independent assortment; genes are linked because they reside on the same chromosome.
Linkage -- analysis of pedigree the tracking of a gene through a family by following the inheritance of a (closely associated) gene or trait and a DNA marker.
Lod score -- logarithm of the odd score; a measure of the likelihood of two loci being within a measurable distance of each other.
Marfan syndrome -- autosomal dominant condition of connective tissue; affects the skeletal, ocular and cardiovascular systems.
Marker -- a gene with a known location on a chromosome and a clear-cut phenotype, used as a point of reference when mapping a new mutant.
Meiosis -- the doubling of gametic chromosome number.
Methylation -- addition of a methyl group (-CH3) to DNA or RNA.
Methylmalonic acidemia -- a group of conditions characterized by the inability to metabolize methylmalonic acid or by a defect in the metabolism of Vitamin B12.
Missense mutation -- a change in the base sequence of a gene that alters or eliminates a protein.
Mitochondrial DNA -- the mitochondrial genome consists of a circular DNA duplex, with 5 to 10 copies per organelle.
Mitosis -- nuclear division.
mRNA -- messnger RNA; an RNA molecular that functions during translation to specify the sequence of amino acids in a nascent polypeptide.
Multifactorial -- a characteristic influenced in its expression by many factors, both genetic and environmental.
Mutation -- process by which genes undergo a structural change.
Myotonic dystrophy -- a combination of progressive weakening of the muscles and muscle spasms or rigidity, with difficulty relaxing a contracted muscle; inherited as an autosomal dominant trait.