Glossary
Genetics glossary
914 definitions · page 11 of 16.
- in vivo
- In a living cell or organism.
- inbreeding
- The mating of genetically related individuals. Mating between relatives.
- inbreeding coefficient (F)
- The probability of homozygosity by descent (having common ancestors). The probability that a zygote obtains copies of the same ancestral gene from both its parents because they are related. The probability of autozygosity.
- inbreeding depression
- A depression of vigour or yield due to inbreeding.
- incestuous
- A mating between blood relatives who are more closely related than the law of the land allows.
- inclusive fitness
- The expansion of the concept of the fitness of a genotype to include benefits accrued to relatives of an individual since relatives share parts of their genomes. Hence an apparently altruistic act toward a relative may in fact enhance the fitness of the…
- incomplete dominance
- The situation in which both alleles of a heterozygote influence the phenotype. The phenotype is usually intermediate between the two homozygous phenotypes. The situation in which a heterozygote shows a phenotype somewhere (but not exactly half-way)…
- independent assortment
- Mendel's second rule describing the independent segregation of alleles of different unlinked or remotely linked loci.
- inducer
- An environmental agent that triggers transcription from an operon.
- inducible operon
- A gene system, often encoding a coordinated group of enzymes involved in a catabolic pathway, is inducible if an early metabolite in the pathway causes activation, usually by interaction with and inactivation of a repressor, of transcription of the genes…
- induction
- 1. The relief of repression for a gene or set of genes under negative control by a repressor. 2. Regarding temperate phages, the process causing a prophage to become virulent. 3. In development, an interaction between two cell lineages to alter the…
- inductive interaction
- The interaction between two groups of cells in which a signal passed from one group of cells causes the other group of cells to change their developmental state (or fate).
- industrial melanism
- The darkening of several species of moths during the recent period of industrialization in many countries by the spread of a gene controlling elevated melanin synthesis.
- infectious transfer
- The rapid transmission of free episomes (plus any host chromosomal genes they may carry) from donor to recipient cells in a bacterial population.
- initiation codon
- The mRNA sequence AUG, which specifies methionine, the first amino acid used in the translation process. (Occasionally GUG, valine, is recognized as an initiation codon).
- initiation complex
- The complex formed for initiation of translation. It consists of the 30S ribosomal subunit; mRNA; N-formyl-methionine tRNA; and three initiation factors .
- initiation factors (IF1 IF2 IF3)
- Proteins (prokaryotic with eukaryotic analogues) required for the proper initiation of translation.
- initiator protein
- Protein that recognizes the origin of replication on a replicon and takes part in primosome construction.
- inosine
- A rare base that is important at the wobble (3rd) position of some tRNA anticodons.
- insertion mutagenesis
- Change in gene activity due to an insertion (of DNA) event that either changes the gene directly or disrupts control mechanisms.
- insertion sequence (IS)
- A mobile piece of bacterial DNA (several hundred nucleotide pairs in length) that is capable of inactivating a gene into which it inserts. Small simple transposons. See transposable genetic element.
- insertional translocation
- The insertion of a segment from one chromosome into another non-homologous chromosome.
- inside marker
- The middle locus of three linked loci.
- intercalary heterochromatin
- Heterochromatin, other than centromeric heterochromatin, dispersed throughout eukaryotic chromosomes.
- intercalating agent
- A chemical that can insert itself between the stacked bases at the centre of the DNA double helix, possibly causing a frameshift mutation.
- interchromosomal recombination
- Recombination resulting from independent assortment.
- interference
- A measure of the independence of crossover events from each other, calculated by subtracting the coefficient of coincidence from 1.
- interference competition
- A form of competition that involves a fight or other active interaction among organisms.
- intergenic suppression
- A mutation at a second locus that apparently restores the wild-type phenotype to a mutation at a first locus.
- interkinesis
- The abbreviated interphase that occurs between meiosis I and II. No DNA replication occurs here.
- interphase
- The cell cycle stage between nuclear divisions, when chromosomes are extended and functionally active. The metabolically active non-dividing stage of the cell cycle.
- interrupted mating
- A technique used to map bacterial genes by determining the sequence in which donor genes enter recipient cells. A gene mapping technique in which bacterial conjugation is disrupted after specified time intervals.
- intersex
- An organism with external sexual characteristics that have attributes of both sexes.
- interstitial region
- The chromosomal region between the centromere and the site of a rearrangement.
- intra-allelic complementation
- The restoration of activity or partial activity (complementation) to an enzyme made of identical subunits (polypeptides encoded by one gene) in a heterozygote of two different mutant alleles of that gene.
- intrachromosomal recombination
- Recombination resulting from crossing over between two linked gene pairs.
- intragenic suppression
- A second mutation within a mutant gene that results in an apparent restoration of the original phenotype.
- intron (intervening sequence)
- A DNA segment of largely unknown function within a gene that specifically interupts the coding (exon) sequences of that gene. Introns are transcribed as part of the normal gene primary transcript, but intron sequences are not found in the functional mRNA…
- inversion
- A chromosomal mutation involving the removal of a chromosome segment, its rotation through l80 degrees, and its reinsertion in the same location. The replacement of a section of a chromosome in the reverse orientation.
- inverted repeat (IR) sequence
- A sequence found in identical (but inverted) form, for example, at the opposite ends of a transposon. A nucleotide sequence found at two sites on the same double helix but in opposite orientation.
- iojap
- A locus in maize that produces variegation.
- ionizing radiation
- Radiation, such as X-rays and gamma rays (high energy photons), that causes atoms to release electrons and become ions.
- isoaccepting tRNA
- The various types of tRNA molecule carrying a specific amino acid.
- isochromosome
- A chromosome with two genetically and morphologically identical arms.
- isoschizomer
- restriction endonuclease that recognizes the same target DNA sequence and cleaves it in the same way.
- isotope
- One of several forms of an element having the same atomic number but differing atomic masses.
- isozyme
- A different electrophoretic form of the same multi-subunit enzyme. Unlike allozymes isozymes are due to differing subunit configurations rather than allelic differences.
- junctional diversity
- Variability in immunoglobulins caused by differences in the exact crossover point during V-J, V-D, and D-J joining.
- kappa particle
- Bacteria-like particle that gives a Paramecium the killer phenotype.
- karyokinesis
- The process of nuclear division. See cytokinesis.
- karyotype
- The chromosome complement of a cell. The entire chromosome complement of an individual or cell, as seen during mitotic metaphase. See idiogram.
- kin selection
- The mode of natural selection that acts on an individual's inclusive fitness.
- kinetochore
- The chromosomal attachment point for the spindle fibers located within the centromeres.
- Klinefelter syndrome
- An abnormal human male phenotype involving an extra X chromosome (XXY).
- lac operon
- An inducible operon including three loci involved in the uptake and breakdown of lactose in Escherichia coli.
- lagging strand
- In DNA replication, the strand that is synthesized apparently in the 3' to 5' direction, but actually in the 5' to 3' direction by ligating short fragments synthesized individually. Strand of DNA being replicated discontinuously. See also leading strand.
- lambda dgal
- A lambda phage carrying a gal(galactose) bacterial gene and defective (d) for some phage function.
- lambda phage
- One kind (species) of temperate bacteriophage.
- lampbrush chromosomes
- Chromosomes of amphibian oocytes having loops suggestive of a lampbrush. Large chromosomes found in amphibian eggs, with lateral DNA loops, extending from chromomeres, producing a brushlike appearance under the microscope.
- lateral inhibition
- The signal produced by one cell that prevents adjacent cells from acquiring their fate.