Insertions are identified by the presence of an additional stretch of base pairs in DNA.
Integralmembrane protein is a protein (noncovalently) inserted into a membrane; it retains its membranous association by means of a stretch of ～25 amino acids that are uncharged and/or hydrophobic.
Integration of viral or another DNA sequence is its insertion into a host genome as a region covalently linkded on either side to the host sequences.
Interallelic complementation describes the change in the properties of a heteromultimeric proteinbrought about by the interaction of subunits coded by two different mutant alleles; the mixed protein may be more or less active than the protein consisting of subunits only of one or the other type.
Interbands are the relatively dispersed regions of polytene chromosomes that lie between the bands.
Intercistronic region is the distance between the termination condon of one gene and the initiation codon of the next gene.
Intermediate component(s) of a ressociation reaction are those reacting between the fast (satellite DNA) and slow (nonrepetitive DNA) components; contain moderately repetitive DNA.
Interphase is the period between mitotic cell divisions; dvivded into G1, S and G2.
Intervening sequence is an intron.
Intron is a segment of DNA that is transcribed, but removed from within the transcript by splicing together the sequences (exons)on either side of it.
Inversion is a chromosomal change in which a segment has been rotated by 180° relative to the regions on either side and reinserted.
Inverted repeats comprise two copies of the same sequence of DNA repeated in opposite orientation on the same molecule. Adjacent inverted repeats constitute a palindrome.
Inverted terminal repeats are the short related or identical sequences present in reverse orientation at the ends of some transposons.
IS is an abbreviation for insertion sequence, a small bacterial transposon carrying only the genetic functions involved in transposition.
Isoaccepting tRNAs represent the same amino acid.
Isotype is a group of closely related immunoglobulin chains.

Karyotype is the entire chromosomal complement of a cell or species (as visualized during mitosis).
kb is an abbreviation for 1000 base pairs of DNA or 1000 bases of RNA.
Kinase is an enzyme that phosphorylates (adds a phosphat group) to a substrate; the substrates for
protein kinases are amino acids in other proteins, and they are divided into those specific for tyrosine and those specific for threonine/serine.
Kinetic complexity is the complexity of a DNA component measured by the kinetics of DNA reassociation.
Kinetochore is the structural feature of the chromosome to which microtubules of the mitotic spindle attach (see also centromere).

Lagging strand of DNA must grow overall in the 3’-5’ direcion and is synthesized discontinuously in the form of short fragments (5’-3’) that are later connected covalently.
Lampbrus chromosomes are the large meiotic chromosomes found in amphibian oocytes.
Lariat is an intermediate in RNA splicing in which a circular structure with a tail is created by a 5’-2’ bond.
Late period of phage development is the part of infection following the start of DNA replication.
Leader is the nontranslated sequence at the 5’ end of mRNA that precedes the initiation codon.
Leader sequence of a protein is a short N-terminal sequence responsible for passage into or through a membrane.
Leading strand or DNA is synthesized continuously in the 5’-3’ direction.
Leaky mutations allow some residual level of gene expression.
Left splicing junction is the boundary between the right end of an exon and the left nd of an intron.
Lethal locus is and gene in which a lethal mutation can be obtained (usually by deletion of the gene).
Library is a set of cloned fragments together representing the entire genome.
Ligation is the formation of a phosphodiester bond to link two adjacent bases separated by a nick in one strand of a double helix of DNA.( The term can also be applied to blunt-end ligation and to joining of RNA).
LINES are long period interspersed sequences in mammalian genomes that are retroposons generated from RNA polymerase II transcripts.
Linkage describes the tendency of genes to be inherited together as a result of their location on the same chromosome; measured by percent recombination between loci.
Linkage group includes all loci that can be connected (directly or indirectly) by linkage relationships; equivalent to a chromosome.
Linkage disequilibrium describes a situation in which some combinations of genetic markers occur more of less frequently in the population than would be expected from their distance apart. It implies that group of markers has been inherited coordinately. It can result from reduced recombination in the region or from a f0under effect, in which there has been insufficient time to reach equilibrium since one of the markers was introduced into the population.
Linker DNA is all DNA contained on a nucleosome in excess of the 146bp core DNA.
Linker fragment is short synthetic synthetic duplex oligonucleotide containing the target sit for some restriction enzyme; may be added to ends of a DNA fragment prepared by cleavage with some other enzyme during reconstructions of recombinant DNA.
Linker scanner mutations are introduced by recombining two DNA molecules in vitro at a restriction fragment added to the end of each; the result is to insert the linker sequence at the site of recombination.
Linking number is the number of times the two strands of a closed DNA duplex cross over each other.
Linking number paradox describes the discrepancy between the existence of –2 supercoils in the path of DNA on the nucleosome compared with the measurement of –1 supercoil released when histones are removed.
Lipids have polar heads, containing phosphate (phospholipid), sterol (such as cholesterol), or saccharide (glycolipid) connected to a hydrophobic tail consisting of fatty acid(s).
Lipid bilayer is the form taken by concentration of lipids in which the hydrophobic fatty acids occupy the interior and the polar heads face the exterior.
Liquid (solution) hybridization is a reaction between complementary nucleic acid strands performed in solution.
Locus is the position on a chromosome at which the gene for a particular trait resides; locus may be occupied by any one of the alleles for the gene.
LODscore is a measure of genetic linkage, defined as the log10 ratio of the probability that the data would have arisen of the loci are linked to the probability that the data could have arisen fom unlined loci. The conventional threshold for declaring linkage is a LOD score of 3.0, that is, a 1000∶1 ratio (which must be compared with the 50∶1 probability that any random pair of loci will be unlinked).
Long-period interspersion is a pattern in the genome in which long stretches of moderately repetitive and which long stretches of moderately repetitive and nonrepetitive DNA alternate.
Loop in a single-stranded region at the end of a hairpin in RNA (or single-stranded DNA); corresponds to the sequence between inverted repeats in duplex DNA.
LTR is an abbreviation for long-terminal repeat, a sequence directly repeated at both ends of a retroviral DNA.
Lumen described the interior of a compartment bounded by membranes, usually the endoplasic reticulum or the mitochondrion.
Luxury genes are those coding for specialized functions synthesized (usually) in large amounts in functions synthesized (usually) in large amounts in particular cell types.
Lysis describes the death of bacteria at the end of a phage infective cycle when they burst open to release the progeny of an infecting phage. Also applies to eukaryotic cells, for example, infected cells that are attacked by the immune system.
Lysogen is a bacterium that possesses a repressed prophage as part of its genome.
Lysogenic immunity is the ability of a prophage to prevent another phage genome of the same type from becoming established in the bacterium.
Lysogenic repressor is the protein responsible for preventing a prophage form reenterin the lytic cycle.
Lysogeny describes the ability of a phage to survive in a bacterium as a stable prophage component of the bacterial genome.
Lysosomes are small bodies, enclosed by membranes, that contain hydrolytic enzymes.
Lytic infection of bacteria by a phage ends in destruction of bacteria and release of progeny phage.

Main band of genomic DNA consists of a broad peak on a density gradient, excluding any visible satellite DNAs that form separate bands.
Major histocompatibility locus is a large chromosomal region containing a gaint cluster of genes that code for transplantation anticgenes and other proteins found on the surfaces of lymphocytes.
Map distance is measured as cM (centiMorgans)= percent recombination (sometimes subject to adjustments).
MAR (matrix attachment site; also known as SAR for scaffold attachment site) is a region of DNA that attaches to the nuclear matrix.
Marker (DNA) is a fragment of known size used to calibrate an electrophoretic gel.
Marker (genetic) is any allele of interest in an experiment.
Maternal inheritance describes the preferential survival in the progeny of genetic markers provided by one parent.
Meisosis occurs by two successive ,divisions (meiosis I and II) that reduce the starting number of (meiosis I and II) that reduce the strting number of 4n chromosomes to 1n in each of four product ells. products may mature to germ cell (sperm or eggs.)