Genetics Terms
Genetics is the study of genes and heredity: how traits pass from parents to offspring and why individuals differ. These terms cover Mendelian inheritance, alleles and genotypes, mutations, chromosomes, and how genes are copied and expressed.
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- AlleleGeneticsAn allele is any of the alternative forms of a gene or DNA sequence that can occupy the same position, or locus, on a chromosome.
- Artificial selectionEvolutionArtificial selection is the process in which people choose which plants or animals breed, so that the traits they want become more common over generations.
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- Bacterial conjugationMicrobiologyBacterial conjugation is the direct transfer of DNA, usually a plasmid, from one bacterial cell to another through a pilus and close cell contact.
- BiotechnologyBiotechnologyBiotechnology is the use of living organisms, cells or their molecules to make products or carry out processes that are useful to people.
- Bottleneck effectEvolutionThe bottleneck effect is the loss of genetic variation that follows a sudden, steep fall in population size, leaving only a few survivors to breed.
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- CancerOncologyCancer is a group of diseases in which abnormal cells divide without control, invade nearby tissue and can spread to distant parts of the body.
- Central dogmaMolecular BiologyThe central dogma is the principle that genetic information flows from DNA into RNA and then into protein, and never back from protein into nucleic acid.
- CentromereCell BiologyA centromere is the constricted region of a chromosome where its two sister chromatids are held together and where spindle fibers attach in cell division.
- ChromosomeGeneticsA chromosome is a thread-like structure of DNA and protein that carries an organism's genes; most human cells hold 46 of them in 23 pairs.
- CodominanceGeneticsCodominance is a pattern of inheritance in which both alleles in a heterozygote are fully expressed, so the traits of both appear together.
- CodonMolecular BiologyA codon is a sequence of three nucleotides in DNA or messenger RNA that stands for one amino acid or tells the ribosome to stop.
- Copy number variationGenomicsCopy number variation is a difference between people in how many copies of a given stretch of DNA their genomes carry, due to deletions or duplications.
- CRISPRBiotechnologyCRISPR is a genome-editing technology, adapted from a bacterial defense system, that uses a guide RNA to direct an enzyme such as Cas9 to cut DNA.
- Crossing overGeneticsCrossing over is the exchange of matching DNA segments between paired homologous chromosomes during meiosis, creating new combinations of alleles.
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- DiploidGeneticsDiploid describes a cell or organism with two complete sets of chromosomes, one inherited from each parent, as in most human body cells.
- DNAMolecular BiologyDNA is the double-stranded molecule that carries the genetic instructions of nearly all living things, written in a code of four bases: A, T, C and G.
- DNA methylationMolecular BiologyDNA methylation is the addition of a small methyl group to DNA, usually on cytosine, which can switch a gene off without changing its sequence.
- DNA profilingForensic MedicineDNA profiling is a laboratory method that identifies a person from highly variable regions of their DNA, used in forensics and kinship testing.
- DNA repairMolecular BiologyDNA repair is the set of processes by which cells detect and correct damage and copying errors in their DNA, protecting the genome from mutation.
- DNA replicationMolecular BiologyDNA replication is how a cell copies all of its DNA before it divides, so that each daughter cell receives a complete genome.
- Dominant alleleGeneticsA dominant allele is a version of a gene whose effect shows in the phenotype even when only one copy is present, masking a recessive allele.
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- EpigeneticsMolecular BiologyEpigenetics is the study of chemical marks on DNA and its packaging proteins that switch genes on or off without changing the DNA sequence.
- EpistasisGeneticsEpistasis is an interaction between genes in which the effect of one gene masks or alters the effect of another gene on the same trait.
- EvolutionEvolutionEvolution is change in the inherited traits of populations over generations, the process that has produced all life's diversity from common ancestors.
- ExomeGenomicsThe exome is the complete set of exons in a genome, its protein-coding part, which makes up only about 1 to 2 percent of human DNA.
- ExonMolecular BiologyAn exon is a section of a gene that stays in the final RNA after splicing removes the introns, and most exons carry code for protein.
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- FitnessEvolutionIn evolution, fitness is an organism's success at surviving and reproducing, measured by its genetic contribution to the next generation.
- Founder effectEvolutionThe founder effect is the loss of genetic variation and shift in allele frequencies that occurs when a few individuals start a new population.
- Frameshift mutationGeneticsA frameshift mutation is an insertion or deletion of DNA bases, in a number not divisible by three, that shifts how the rest of a gene's codons are read.
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- GameteDevelopmental BiologyA gamete is a haploid reproductive cell, such as a sperm or an egg, that fuses with a gamete of the opposite type at fertilization to form a zygote.
- GeneGeneticsA gene is a stretch of DNA that carries the instructions for making a protein or a working RNA molecule, and is the basic unit of heredity.
- Gene expressionMolecular BiologyGene expression is the use of a gene's information to make a working product, usually a protein or a functional RNA molecule.
- Gene flowEvolutionGene flow is the movement of alleles from one population into another when individuals or their gametes migrate and then breed.
- Gene therapyBiotechnologyGene therapy is a treatment that changes the genes inside a patient's cells, by adding, replacing, silencing or editing DNA, to treat or prevent disease.
- Genetic driftEvolutionGenetic drift is a random change in allele frequencies from one generation to the next, caused by chance rather than by natural selection.
- Genetic engineeringBiotechnologyGenetic engineering is the direct change of an organism's DNA using laboratory techniques, to add, remove or alter genes and give it new traits.
- Genetic linkageGeneticsGenetic linkage is the tendency of genes that lie close together on the same chromosome to be inherited together rather than sorted independently.
- Genetically modified organismBiotechnologyA genetically modified organism is a plant, animal or microbe whose DNA has been changed by genetic engineering in a way mating could not achieve.
- GenomeGenomicsA genome is the complete set of DNA in an organism or cell, including all of its genes and the stretches of DNA between them.
- Genome-wide association studyGenomicsA genome-wide association study (GWAS) scans the genomes of many people to find genetic variants that are more common in those with a trait or disease.
- GenotypeGeneticsA genotype is the genetic makeup of an organism, either at one locus, such as Aa, or across its whole genome, including alleles it does not express.
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- HaploidGeneticsHaploid describes a cell or organism that has a single set of chromosomes, such as a human egg or sperm cell with 23 chromosomes.
- Hardy–Weinberg equilibriumGeneticsHardy–Weinberg equilibrium is the state in which allele and genotype frequencies in a population stay constant from one generation to the next.
- HeterozygousGeneticsHeterozygous describes an organism that carries two different alleles of a gene at a given locus, such as one dominant and one recessive allele.
- HomozygousGeneticsHomozygous describes an organism that carries two identical alleles of a gene at a given locus, one inherited from each parent.
- Hox genesDevelopmental BiologyHox genes are a family of genes coding for transcription factors that give each region along an animal's head-to-tail axis its identity during development.
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- Incomplete dominanceGeneticsIncomplete dominance is a pattern of inheritance in which a heterozygote has a phenotype intermediate between those of the two homozygotes.
- IntronMolecular BiologyAn intron is a stretch of a gene that is copied into RNA but cut out by splicing before the RNA is used, so it does not code for protein.
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- Major histocompatibility complexImmunologyThe major histocompatibility complex is a set of genes whose proteins display protein fragments on cell surfaces so that T cells can inspect them.
- MeiosisCell BiologyMeiosis is a two-stage cell division that turns one diploid cell into four genetically different haploid cells, the precursors of eggs and sperm.
- Mendelian inheritanceGeneticsMendelian inheritance is the pattern by which single genes pass from parents to offspring, following the laws of segregation and independent assortment.
- Messenger RNAMolecular BiologyMessenger RNA is the RNA copy of a gene that carries protein-building instructions from DNA to the ribosomes, where it is read in three-base codons.
- MicroRNAMolecular BiologyA microRNA is a short RNA, about 22 nucleotides long, that does not code for protein but silences genes by pairing with their messenger RNAs.
- MitosisCell BiologyMitosis is the division of a cell's nucleus that gives each of two daughter cells an identical, complete set of chromosomes.
- MutationGeneticsA mutation is a lasting change in an organism's DNA sequence, ranging from a single altered base to large rearrangements of chromosomes.
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- Natural selectionEvolutionNatural selection is the process by which inherited traits that improve survival and reproduction become more common in a population over generations.
- NondisjunctionGeneticsNondisjunction is the failure of paired chromosomes or sister chromatids to separate in cell division, leaving cells with the wrong chromosome number.
- NucleotideBiochemistryA nucleotide is a single unit of DNA or RNA, made of a nitrogen-containing base, a five-carbon sugar and one or more phosphate groups.
- NucleusCell BiologyThe nucleus is the membrane-bound organelle that holds a eukaryotic cell's chromosomes and controls which of its genes are used and when.
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- OncogeneOncologyAn oncogene is a mutated or overactive form of a normal growth-promoting gene that pushes cells to divide uncontrollably and can cause cancer.
- OperonMolecular BiologyAn operon is a cluster of genes in bacteria that share one promoter, are switched on and off together and are copied into a single messenger RNA.
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- PedigreeGeneticsA pedigree is a family tree chart that shows how a trait or genetic condition is passed down through the generations of a family.
- PhenotypeGeneticsA phenotype is the set of observable traits of an organism, such as its height or blood group, produced by its genotype acting with its environment.
- Polygenic inheritanceGeneticsPolygenic inheritance is the inheritance of a trait controlled by many genes, each with a small effect, giving continuous variation such as height.
- PromoterMolecular BiologyIn molecular biology, a promoter is a stretch of DNA, usually just upstream of a gene, where RNA polymerase binds so that transcription can begin.
- Punnett squareGeneticsA Punnett square is a grid used in genetics to predict the possible genotypes of offspring, and how likely each is, from the alleles of two parents.
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- Recessive alleleGeneticsA recessive allele is a version of a gene whose effect appears only when an organism has two copies, because a single dominant allele masks it.
- RNAMolecular BiologyRNA is a usually single-stranded nucleic acid, built with the sugar ribose and the base uracil, that carries and uses genetic information to make proteins.
- RNA splicingMolecular BiologyRNA splicing is the step in which introns are cut out of a newly made RNA and its exons are joined, producing a mature RNA ready for use.
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- Sickle cell diseaseMedicineSickle cell disease is an inherited blood disorder in which abnormal hemoglobin bends red blood cells into stiff crescents that block small blood vessels.
- Single nucleotide polymorphismGenomicsA single nucleotide polymorphism (SNP) is a position in the genome where people differ by a single DNA base, the most common kind of genetic variation.
- Southern blotMolecular BiologyA Southern blot is a laboratory method that finds a specific DNA sequence by separating DNA fragments on a gel, moving them to a membrane and probing them.
- SpeciationEvolutionSpeciation is the evolutionary process in which one ancestral species splits into two or more species whose members can no longer interbreed.
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- TranscriptionMolecular BiologyTranscription is the process in which a cell copies the DNA sequence of a gene into a matching strand of RNA.
- Transgenic organismBiotechnologyA transgenic organism is a living thing, such as a crop, mouse or bacterium, whose genome carries DNA from another species added by genetic engineering.
- TransposonGeneticsA transposon is a DNA sequence that can move from one place in a genome to another, in some cases leaving a copy behind as it goes.
- Tumor suppressor geneOncologyA tumor suppressor gene makes a protein that restrains cell division or repairs damage, so losing both working copies can help a cell turn cancerous.
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