Science / Genetics Glossary

3-End: The end of a polynucleotide with a free (or phosphorylated) 3' - hydroxyl group.

5-End: The end of a polynucleotide with a free (or phosphorylated or capped) 5' - hydroxyl group: transcription/translation begins at this end.

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 do . . . View Full Definition

Additive Genetic Effects: When the combined effects of alleles at different loci are equal to the sum of their individual effects.

Adenine (A): A nitrogenous base, one member of the base pair a- t (adenine- thymine).

Advanced Maternal Age: Women over age 34 (age 35 at delivery) at increased risk for nondisjunction trisomy in fetus.

Affected Relative Pair: Individuals related by blood, each of whom is affected with the same trait. Examples are affected sibling, cousin, and avuncular pairs.

Aggregation Technique: A technique used in model organism studies in which embryos at the 8-cell stage of development are pushed together to yield a single embryo (used as an alternative to microinjection).

Alcoholism: A chronic and progressive condition characterized by the inability to control the consumption of alcohol.

Allele: Alternative form of a genetic locus: a single allele for each locus is inherited from each parent (e.g., at a locus for eye color the allele might result in blue or brown eyes).

Allogeneic: Variation in alleles among members of the same species.

Alpha-Fetoprotein (AFP): A protein excreted by the fetus into the amniotic fluid and from there into the mother's bloodstream through the placenta.

Alternative Splicing: Different ways of combining a gene's exons to make variants of the complete protein

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 endo . . . View Full Definition

Amino Acid: Any of a class of 20 molecules that are combined to form proteins in living things. The sequence of amino acids in a protein and hence protein function are determined by the genetic code.

Amino Acid Sequence: The linear order of the amino acids in a protein or peptide.

Amniocentesis: 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.

Amniocyte: Cells obtained by amniocentesis.

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