Glossary - The Basics

  • DNA: Deoxyribonucleic acid. DNA is a molecule composed of two chains that coil around each other to form a double helix carrying the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms.

  • Gene: A sequence of DNA that codes for a molecule that has a function. The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic traits.

  • Chromosome: A chromosome is a DNA molecule with part or all of the genetic material (genome) of an organism.

  • Allele: An allele is a variant form of a given gene. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation. Humans have two sets of chromosomes (one from the mother, another from the father), that is, we are diploid. If both alleles at a gene are the same (e.g. GG-TT), they are homozygous. If the alleles are different, they are heterozygous.

  • Genotype: The genotype is the part of the genetic makeup of a cell, and therefore of any individual, which determines one of its characteristics (phenotype). It holds all the genetic information received from the parents, and that combined with environmental factors determine the phenotype.

  • Phenotype: The composite of an organism's observable characteristics or traits, such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior (such as a bird's nest). A phenotype results from the expression of an organism's genetic code, its genotype, as well as the influence of environmental factors and the interactions between the two.

  • Polymorphism: The occurrence of two or more clearly different forms, also referred to as alternative phenotypes, in the population of a species. SNPs (single nucleotide polymorphisms) are variations in a single nucleotide that occurs at a specific position in the genome, where each variation is present to some appreciable degree within a population.