Amino acid Building block of protein molecules. Also important components of our diet.
Amniotic fluid The liquid surrounding a fetus in its mother’s womb; enclosed by the amniotic membrane. The amniotic membrane and its contents constitute the amnion.
Antibiotic A chemical that inhibits bacterial or fungal proliferation.
Antibody A protein molecule synthesized in the cells of the immune system whose role it is to neutralize antigens.
Anticodon The portion of a tRNA molecule that recognizes a specific codon.
Antigen Any substance recognized as foreign by the immune system.
Bacteriophage Also called a phage. A virus that infects bacteria.
Base substitution A change of base pair in DNA.
Biolistics A technique to introduce DNA into plant cells. Metal particles on which DNA is adsorbed are shot into cells, usually by means of a gas-driven piston.
Blastocyst A young embryo composed of several dozen cells containing a cavity in its center.
Catalyst A compound that accelerates chemical reactions.
Chorionic villus Embryonic tissue surrounding the amnion.
Chromosome A structure composed of DNA and protein which is visible under the microscope in dividing cells.
Clone Identical copies of DNA, or genetically identical cells or organisms.
Cloning 1. The act of isolating and multiplying a certain piece of DNA containing one or more specific genes. 2. The act of producing one or several identical cells or organisms from a single cell or organism.
Codominance A situation in which two different versions of the same gene are equally expressed and have equal contribution to phenotype.
Codon A set of three contiguous base pairs in DNA (or three bases in RNA) that corresponds to a specific amino acid. There are sixty-four possible codons from the four DNA building blocks arranged in sets of three.
Complementary base pairing Pairing between A and T or G and C in DNA or A and U or G and C in RNA.
Cross A sexual mating producing offspring.
Deletion A mutation caused by the removal of one or more base pairs in a gene.
Deoxyribose A six-carbon sugar present in DNA.
Diploid A cell or organism containing two complete sets of chromosomes.
DNA ligase An enzyme used to glue together two pieces of DNA.
DNA polymerase The enzyme that replicates DNA.
Dominant A gene or trait that is phenotypically expressed and masks the phenotype of another gene or trait.
Drift In small populations, refers to the fact that by chance alone some gene variants can become prevalent while others can become rare or go extinct.
Electrophoresis A technique that separates molecules such as proteins and DNA fragments in an electric field.
Embryo An organism containing tens of cells resulting from the fusion of an egg and a sperm cell. An embryo develops into a fetus after many cell divisions.
Enzyme A biological catalyst that accelerates a specific chemical reaction.
Evolution Modification of organisms by a selection process acting on variation among individuals.
DNA fingerprinting A technique that can identify a single individual by his/her/its DNA profile.
Fitness The ability of individuals with particular phenotypes to pass on their genes to the next generation. This ability is dependent on both the genetic makeup of the individual and the environment.
Founder effect The genetic results of the creation of a new population by a few members from a larger population.
Gametes Haploid cells that fuse to form an individual. Sperm, eggs, pollen grains, and ovules are gametes.
Gene The basic unit of heredity. Genes are composed of DNA.
Gene therapy A method of treating a genetic disease by providing a patient with a correct version of a defective gene.
Genetic code The code containing the information in DNA used to produce proteins.
Genetic engineering The act of introducing one or several new genes into an organism.
Genetically modified organism Any organism containing one or several genes normally not found in that organism. The introduced gene can be from another organism or a gene from the same organism with modifications.
Genome The suite of all genes in an organism.
Genotype The types of gene combinations, dominant or recessive, of an organism. Often shown for a single trait or a few traits using upper- and lowercase letters.
GMO See genetically modified organism.
Haploid A cell or organism containing only a single set of chromosomes.
Hermaphrodite An organism in which one individual produces both male and female gametes. Some can self-fertilize. Most plants and some animals are hermaphrodites.
Heterogametic Individuals that have two different types of sex chromosomes. In humans, the heterogametic sex is male, with an X chromosome and the Y chromosome. Among birds, the heterogametic sex is female, with two different sex chromosomes.
Heterozygote Individual containing two different copies of a given gene, such as Aa.
Homogametic Individuals that have two of the same type of sex chromosomes. In humans, the homogametic sex is female, with two X chromosomes. Among birds, the homogametic sex is male with two matching sex chromosomes.
Homozygote Individual containing two identical copies of a given gene, such as AA or aa.
Insertion A mutation caused by the addition of one or more base pairs to a gene.
Linkage A situation in which genes are located on the same chromosome.
Meiosis The special cell division that produces gametes. The process produces four haploid cells, that is, cells with half the number of chromosomes of the diploid progenitor cell.
Messenger RNA Also abbreviated mRNA; an RNA copy of a DNA gene made by the process of transcription.
Metabolic disease A disease in which affected individuals are unable to metabolize certain compounds present in the cells.
Migration Population movement that results in mixing one population with another.
Mitochondrion (pl. mitochondria) Cellular organelles that generate energy using oxygen.
Mitosis Cell division that produces two cells identical in genetic composition to the progenitor cell.
mRNA See messenger RNA
Mutagen A substance or physical effect that causes mutations above and beyond the spontaneous mutation rate.
Mutation A change in DNA base-pair sequence.
Natural selection Conditions in nature that increase or decrease the chance for individuals of certain phenotypes to pass on their genes to the next generation.
Nitrogenous base A term used to refer to the part of the DNA and RNA molecules that include A, G, C, T and U. They are called nitrogenous bases because they contain nitrogen atoms.
Nucleotide The combination of a nitrogenous base with ribose or deoxyribose and a phosphate group.
Nucleus The part of the cell where most of its DNA is located.
Palindrome A word or DNA sequence that reads the same forward and backward. With DNA, the sequence reads the same going forward in the one strand and backward in the other strand of the double helix.
Example: GCATATGC
GCATATGC
Pathogen An organism that causes disease.
PCR See polymerase chain reaction.
Pedigree A compendium of relationships among individuals in a family; a family tree.
Phenotype The physical properties of an organism. Many phenotypes are under the control of genes, but some are not. Examples of phenotypes are: flower color in plants, the ability or inability to metabolize the sugar galactose in humans, coat color in dogs, and so on.
Phenylketonuria A genetic disease characterized by the inability to metabolize the amino acid phenylalanine.
Phytoremediation The action of cleaning polluted soils with plants.
Plasmid A circular piece of double-stranded DNA much smaller than the genetic material in chromosomes. Plasmids are used for genetic engineering.
Pluripotent A cell that can differentiate into many different types of cells in the body.
Polymer A substance made of a large number of repeating subunits.
Polymerase chain reaction Abbreviated PCR; a technique allowing DNA replication in the test tube.
Polymorphism Things that exist in different variants in the population, for example, genes or DNA sequences.
Population A collection of individuals found in the same geographic location and where mating among individuals is possible.
Primer A short piece of single stranded DNA complementary to a piece of DNA that allows initiation of its replication.
Promoter A DNA sequence situated just before a gene whose function is to bind RNA polymerase.
Proofreading enzymes enzymes that scan newly synthesized DNA for potential base-pairing errors.
Protein A polymer composed of amino-acid building blocks.
Random genetic drift See drift.
Recessive The opposite of dominant. A recessive trait is only seen, that is, phenotypically expressed, in an individual without a dominant trait. This situation arises when one has two copies of the recessive trait or when the heterogametic sex has just one copy of the recessive trait on one sex chromosome.
Recombinant DNA DNA made in the test tube containing genes originating from different sources.
Recombination Shuffling genetic information by cutting and pasting DNA strands.
Replication The act of copying each strand of the DNA to produce two double-stranded DNA from one double-stranded DNA.
Restriction enzyme An enzyme that cuts double-stranded DNA at a specific sequence.
Ribose A six-carbon sugar found in building blocks of RNA.
Ribosome A small cellular structure that makes proteins encoded by mRNA and is thus involved in translation. The ribosome is composed of RNAs and proteins.
RNA polymerase An enzyme that makes RNA. It can make RNA copies of DNA genes through the mechanism of transcription.
Segregation Separation of two copies of a gene in meiosis.
Selfing The action of self-fertilization. Can commonly occur in the plant world.
Strain A collection of identical cells derived from one single cell and possessing the same phenotype and genotype. A strain is in fact a clone.
Template A DNA strand that serves as blueprint during DNA replication and transcription.
Teratogen A substance that produces malformations in a developing fetus without affecting its genetic material.
Terminator A DNA sequence at the end of a gene that indicates the end of the gene and signals the end of transcription.
Trait A particular phenotype such as eye color, height, hairy leaves, and so on.
Transcription The act of making an RNA copy of a DNA gene.
Transfer RNA A small RNA molecule that binds a specific amino acid and deciphers a codon in the mRNA.
Transformation The act of introducing DNA into living cells.
Translation The act of making protein molecules encoded by messenger RNA.
Triploid A cell or organism containing three sets of chromosomes.
Zygote The product of fertilization of an egg by a sperm cell.