Glossary

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Blastocyst: embryo development stage characterized by the formation of a cavity inside the morula (set of embryonic cells): the blastoclium. ES cells can be injected in blastocysts to create chimeras or transgenic animals  


Chimera: organism that contains cells or tissues with different genotypes


Chromosome: one or more large macromolecules in which genetic information (DNA) is normally packaged in


Deletion: excision of a DNA fragment, as opposed to insertion; mutation occurring naturally, but also artificially by using a molecular biological strategy


DNA: Deoxyribonucleic acid; Molecule that encodes genetic information; main component of the chromosomes; DNA is a double-stranded helix held together by bonds between pairs of nucleotides.


DNA sequencing: The relative order of base pairs, whether in a DNA fragment, gene, chromosome, or an entire genome. The instrumentation and procedures used to determine the order of nucleotides in DNA.    


ES cells: Embryonic stem cells. Cultured cells derived from the pluripotent inner cell mass of blastocyst stage embryos. Used for gene targeting by homologous recombination


Fertilized mouse egg: embryo at "one cell" stage of development


Gene: DNA sequence encoding one particular protein


Genetic code: used by the cells to translate genetic information in a protein sequence; three successive nucleotides in a gene form one codon, and each codon calls for a single amino acid. For example, the set AUG (adenine, uracil, guanine) calls for the amino acid methionine. The sequence of codons along a gene specifies the sequence of amino acids in a particular protein. Instructions appearing in the genes are converted (transcription) in RNA, and then translated (translation) in protein


Gene expression: mechanism by which gene information is used to create one protein


Gene product: protein encoded by a gene


Gene targeting: molecular biological strategy that allows a point intervention in the genome, at the level of a clearly delimited sequence, as opposed to classical transgenesis


Genome: genetic heritage from an individual or species; the set of genes that ensures transmission of hereditary characteristics


Genomic: study of genes and their functions


Genotype: genetic profile indicating the particular characteristics of the genome of an organism


Germ cells: sperm and egg cells, and their precursors. Germ cells are haploid (only one set of chromosomes, while the other somatic cells have two copies) and transmit the genetic characteristics to the lineage


Homologous recombination: exchange of genetic material between two DNA fragments presenting sequence homologies


Inducible: transcription of some genes can be triggered by inducers, small molecules able to act on regulating sequences of these genes


Insertion: genetic mutation by introduction of one or more nucleotides in a DNA sequence


Knock-in: describes a mouse in which one particular gene sequence has been replaced by another


Knock-out: describes a mouse in which one particular gene sequence has been modified to block gene expression


Micro-injection: technology used in the laboratory to introduce a transgene into fertilized mouse eggs


Mutation: change in nucleotide sequence of DNA


Nuclear transfer: technology where a nucleus from one cell is transferred into an enucleated cell (most of the time an embryo).


Nucleotide: elementary component of nucleic acids (DNA or RNA), consisting of a nitrogenous base, purine (adenine A; guanine G) or pyrimidine (cytosine C; thymine T in DNA, or uracil U in RNA), associated with phosphate and a sugar molecule (deoxyribose in DNA and ribose in RNA)


Pluripotency: a pluripotent cell is able to differentiate into many cell types. eg. stem cells


Predictability: property of a research system (e.g., an animal model) to mimic human physiology. A model of high predictability provides researchers with results that are closer to those they would obtain directly if they could perform the experiments in humans.


Protein: molecule composed of amino acids; for each protein, the order of the amino acids is related to the chain of the codons (groups of three nucleotides) from the gene encoding this protein; obtained by the translation mechanism; see also genetic code


Promoter: DNA sequence regulating gene expression; the nature of the promoter determines which transcription effectors will stimulate or repress the gene. The promoters can be functional in a tissue-specific manner, or activated in particular biological conditions


RNA: Ribonucleic acid; molecule similar to DNA and implicated in cellular mechanisms of genetic information deciphering; obtained by the transcription process


Somatic cells: somatic line includes all the body cells except germ cells. NB: gene therapy in humans concerns only somatic cells


Totipotency: the ability of a single cell, usually a stem cell, to divide and produce all the differentiated cells in an organism.


Translation: cellular process by which protein synthesis from RNA is achieved


Transcription: cellular process by which DNA is converted to RNA


Transgene: gene artificially introduced into the cell or into the genome of an individual


Transgenic: organism (mouse) whose genome has been altered by the inclusion of foreign genetic material  


Vector: tool (particular DNA sequence) permitting the transport of foreign or modified DNA