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Glossary

Glossary

Allele: alternate forms of a genetic locus. For example, at a locus determining eye color, an individual might have the allele for blue eyes, brown, etc.

Antioxidant: an enzyme or other organic substance that is capable of slowing or preventing the damaging effects of oxidation – a chemical process resulting in free radicals, which cause cell-damaging reactions. Vitamin A, Vitamin E, and the carotenes are examples of antioxidants.

Base: one of the four nitrogenous subunits (nucleotides) of DNA: adenine (abbreviated as A), guanine (G), cytosine (C), and thymine (T). In the DNA molecule, they are linked to one another in pairs of long chains, where each member of the pair is complementary to the other. This double-stranded chain is itself twisted into a double helix. The complementarity between the strands is brought about by the interaction between A and T, and between G and C. Since the identity of a base on one strand can be used to infer the identity of the corresponding base on the other strand, the terms “base” and “base pair” are often used interchangeably. The number of bases (or base pairs) is used as a measurement of the size of a genome. For example, the length of the human genome is approximately 3 billion base pairs (abbreviated bp).

Biofuel:  fuel that is derived from a living or recently living organism, as opposed to fossil fuels, which are produced from the altered remains of long-dead animals.

Carotenoids: organic pigments occurring in plants, such as carotene, many of which can be converted to Vitamin A in humans.

Chromosome: the structure in the eukaryotic nucleus and in the prokaryotic cell that carries most of the DNA.

Cytogenetics: the study of chromosome shape and function.

Dioecious: a plant that has only male or female parts (and therefore cannot self-fertilize).

DNA: an abbreviation for “deoxyribonucleic acid”, the carrier molecule of genetic information. The chain of nucleotides is held together on a polymer backbone formed by a sugar (deoxyribose) and a phosphate group (see also base).

DNA sequence: the specific order of the nucleotide bases that make up DNA (see also DNA and base).

Domestication:  the process by which plants and animals are genetically modified over time by humans for traits that are more advantageous for humans.

Dominant: (as refers to gene action) the allele that masks the effect of another allele when present in a heterozygote state.

Fertilization: the union of male and female gametes to form a zygote, initiating biological reproduction.

Gamete: a mature sexual reproductive cell, as a sperm or egg, that unites with another cell during fertilization to form a new organism.

Gene: a unit of heredity, transmitted from generation to generation during reproduction. Each gene consists of a sequence of nucleotides, occupying a specific position along a chromosome. Most genes encodes a specific functional product.

Genetic diversity: the differences among organisms at the gene or DNA level.

Genome: all the genetic material of an organism.

Genotype: the inherited genetic constitution of an organism, see also phenotype.

Germplasm: seeds or other material from which plants can be propagated; the collection of a set of genetic resources for an organism, which for plants can consist of a seed collection or plant nursery.

Heterosis or hybrid vigor: progeny that are bigger and healthier than either of their parents as a  result of the cross-breeding of genetically different parents (the opposite of inbreeding depression).

Heterozygous: contains different alleles at a particular locus of the genome.

Homozygous: contains identical alleles at a particular locus of the genome.

Hybrid vigor: see heterosis.

Inbreeding depression: the loss of health or vigor resulting from the cross-breeding of genetically similar parents.

Inheritance: the set of genetic characteristics passed on from parents to progeny.

Locus: the position of a gene or mutation on a chromosome.

Meiosis: part of the sexual reproduction process where cell division occurs such that the diploid chromosome number is reduced to form haploid gametes.

Monoecious: a plant that has both female and male parts (see also dioecious).

Mutations: changes to one or more nucleotides in the DNA sequence; an abrupt change in the genotype of an organism that is not the result of recombination.

Nucleotide: the unit of DNA, consisting of one base, one phosphate molecule, and the sugar  deoxyribose. See also base.

Pathogen: a disease-causing agent (e.g. bacteria, virus, insect, etc.).

PCR: abbreviation for “polymerase chain reaction”, the process by which a defined fragment of DNA is replicated in vitro in a so-called thermocycler or PCR machine. It provides a quick, inexpensive way of making a large number (millions) of copies of a specific DNA segment.

Phenotype: the visible appearance of an organism. The phenotype reflects the combined action of the genotype and the environment where the individual exists.

Pollen: powder containing the male gametes of plants, the fertilizing element of flowering plants.

Polyploidy: a state in which multiple copies of a complete genome are present. Polyploidy is rare in animals, but common in plants. In animals (and also plants) some tissues within a diploid organism can be polyploidy (see also ploidy).

Ploidy: the number of complete sets of chromosomes in each cell in an organism. The ploidy series is haploid (1 copy), diploid (2 copies), triploid (3 copies), tetraploid (4 copies), pentaploid (5 copies), hexaploid (6 copies) etc. (see also polyploidy).

Progenitor: parent, ancestor, predecessor.

Progeny: offspring, children.

Recessive: the allele that can be masked by an alternative allele in the heterozygote state, such that the phenotype of a recessive allele may only be identified in the homozygote state.

Quantitative trait: a trait or characteristic that cannot be accounted for by only one gene but rather is governed by several or many genes working together.

Seed dormancy: a condition that prevents seeds from germinating under certain conditions.

Shattering: nonretention of seed by a plant; seed dispersal. Necessary for plants in the wild, but disadvantageous for harvesting (the seeds fall to the ground and are more difficult to harvest).

SNP: an abbreviation for “single nucleotide polymorphism”, pronounced "snip". A SNP that distinguishes two sequences can be used as a genetic marker.

Teosinte (Zea mays ssp. huehuetenangensis, ssp. mexicana, ssp. parviglumis and others) is a wild grass in the Poaceae family that is the ancestor of maize (Zea mays ssp. mays).

Transgenic: an organism containing genetic material from another organism transferred by genetic engineering.


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