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Rockefeller - Genetics Glossary Category: Sciences > Glossary of Genetics Date & country: 12/08/2008, USA Words: 133

g
A nitrogenous base, one member of the base pair G- C (guanine and cytosine).

e. coli
Common bacterium that has been studied intensively by geneticists because of its small genome size, normal lack of pathogenicity, and ease of growth in the laboratory.

c
A nitrogenous base, one member of the base pair G- C (guanine and cytosine).

a
A nitrogenous base, one member of the base pair A- T (adenine- thymine).

yac
A vector used to clone DNA fragments (up to 400 kb); it is constructed from the telomeric, centromeric, and replication origin sequences needed for replication in yeast cells. Compare cloning vector, cosmid.

vlsi
Very large- scale integration allowing over 100,000 transistors on a chip.

virus
A noncellular biological entity that can reproduce only within a host cell. Viruses consist of nucleic acid covered by protein; some animal viruses are also surrounded by membrane. Inside the infected cell, the virus uses the synthetic capability of the host to produce progeny virus.

uracil
A nitrogenous base normally found in RNA but not DNA; uracil is capable of forming a base pair with adenine.

translation
The process in which the genetic code carried by mRNA directs the synthesis of proteins from amino acids. Compare transcription.

transformation
A process by which the genetic material carried by an individual cell is altered by incorporation of exogenous DNA into its genome.

trna
A class of RNA having structures with triplet nucleotide sequences that are complementary to the triplet nucleotide coding sequences of mRNA. The role of tRNAs in protein synthesis is to bond with amino acids and transfer them to the ribosomes, where proteins are assembled according to the genetic code carried by mRNA.

transcription
The synthesis of an RNA copy from a sequence of DNA (a gene); the first step in gene expression. Compare translation.

telomere
The ends of chromosomes. These specialized structures are involved in the replication and stability of linear DNA molecules. See DNA replication.

technology transfer
The process of converting scientific findings from research laboratories into useful products by the commercial sector.

tandem repeat sequences
Multiple copies of the same base sequence on a chromosome; used as a marker in physical mapping.

sts
Short (200 to 500 base pairs) DNA sequence that has a single occurrence in the human genome and whose location and base sequence are known. Detectable by polymerase chain reaction, STSs are useful for localizing and orienting the mapping and sequence data reported from many different laboratories and serve as landmarks on the developing physical ma...

southern blotting
Transfer by absorption of DNA fragments separated in electrophoretic gels to membrane filters for detection of specific base sequences by radiolabeled complementary probes.

somatic cells
Any cell in the body except gametes and their precursors.

shotgun method
Cloning of DNA fragments randomly generated from a genome. See library, genomic library.

sex chromosomes
The X and Y chromosomes in human beings that determine the sex of an individual. Females have two X chromosomes in diploid cells; males have an X and a Y chromosome. The sex chromosomes comprise the 23rd chromosome pair in a karyotype. Compare autosome.

rrna
A class of RNA found in the ribosomes of cells.

sequencing
Determination of the order of nucleotides (base sequences) in a DNA or RNA molecule or the order of amino acids in a protein.

rna
A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell. The structure of RNA is similar to that of DNA. There are several classes of RNA molecules, including messenger RNA, transfer RNA, ribosomal RNA, and other small RNAs, each serving a different purpose.

ribosomes
Small cellular components composed of specialized ribosomal RNA and protein; site of protein synthesis. See ribonucleic acid (RNA).

rflp
See restriction fragment length polymorphism.

rflp
Variation between individuals in DNA fragment sizes cut by specific restriction enzymes; polymorphic sequences that result in RFLPs are used as markers on both physical maps and genetic linkage maps. RFLPs are usually caused by mutation at a cutting site. See marker.

restriction enzyme cutting site
A specific nucleotide sequence of DNA at which a particular restriction enzyme cuts the DNA. Some sites occur frequently in DNA (e.g., every several hundred base pairs), others much less frequently (rare- cutter; e.g., every 10,000 base pairs).

resolution
Degree of molecular detail on a physical map of DNA, ranging from low to high.

regulatory regions or sequences
A DNA base sequence that controls gene expression.

recombination
The process by which progeny derive a combination of genes different from that of either parent. In higher organisms, this can occur by crossing over.

recombinant dna technologies
Procedures used to join together DNA segments in a cell- free system (an environment outside a cell or organism). Under appropriate conditions, a recombinant DNA molecule can enter a cell and replicate there, either autonomously or after it has become integrated into a cellular chromosome.

recombinant clones
Clones containing recombinant DNA molecules. See recombinant DNA technologies.

pyrimidine
A nitrogen- containing, double- ring, basic compound that occurs in nucleic acids. The pyrimidines in DNA are cytosine and thymine; in RNA, cytosine and uracil.

purine
A nitrogen- containing, single- ring, basic compound that occurs in nucleic acids. The purines in DNA and RNA are adenine and guanine.

protein
A large molecule composed of one or more chains of amino acids in a specific order; the order is determined by the base sequence of nucleotides in the gene coding for the protein. Proteins are required for the structure, function, and regulation of the bodys cells, tissues, and organs, and each protein has unique functions. Examples are hormones, e...

promoter
A site on DNA to which RNA polymerase will bind and initiate transcription.

prokaryote
Cell or organism lacking a membrane- bound, structurally discrete nucleus and other subcellular compartments. Bacteria are prokaryotes. Compare eukaryote. See chromosomes.

probe
Single- stranded DNA or RNA molecules of specific base sequence, labeled either radioactively or immunologically, that are used to detect the complementary base sequence by hybridization.

primer
Short preexisting polynucleotide chain to which new deoxyribonucleotides can be added by DNA polymerase.

polymorphism
Difference in DNA sequence among individuals. Genetic variations occurring in more than 1% of a population would be considered useful polymorphisms for genetic linkage analysis. Compare mutation.

polymerase
Enzymes that catalyze the synthesis of nucleic acids on preexisting nucleic acid templates, assembling RNA from ribonucleotides or DNA from deoxyribonucleotides.

polygenic disorders
Genetic disorders resulting from the combined action of alleles of more than one gene (e.g., heart disease, diabetes, and some cancers). Although such disorders are inherited, they depend on the simultaneous presence of several alleles; thus the hereditary patterns are usually more complex than those of single- gene disorders. Compare single- gene ...

plasmid
Autonomously replicating, extrachromosomal circular DNA molecules, distinct from the normal bacterial genome and nonessential for cell survival under nonselective conditions. Some plasmids are capable of integrating into the host genome. A number of artificially constructed plasmids are used as cloning vectors.

pl. loci
The position on a chromosome of a gene or other chromosome marker; also, the DNA at that position. The use of locus is sometimes restricted to mean regions of DNA that are expressed. See gene expression.

physical mapping
A map of the locations of identifiable landmarks on DNA (e.g., restriction enzyme cutting sites, genes), regardless of inheritance. Distance is measured in base pairs. For the human genome, the lowest- resolution physical map is the banding patterns on the 24 different chromosomes; the highest- resolution map would be the complete nucleotide sequen...

phage
A virus for which the natural host is a bacterial cell.

pcr
A method for amplifying a DNA base sequence using a heat- stable polymerase and two 20- base primers, one complementary to the (+)- strand at one end of the sequence to be amplified and the other complementary to the (- )- strand at the other end. Because the newly synthesized DNA strands can subsequently serve as additional templates for the same ...

nucleus
The cellular organelle in eukaryotes that contains the genetic material.

nucleotide
A subunit of DNA or RNA consisting of a nitrogenous base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). Thousands of nucleotides are linked to form a DNA or RNA molecule. See DNA, base pair, RNA.

nucleic acid
A large molecule composed of nucleotide subunits.

nitrogenous base
A nitrogen- containing molecule having the chemical properties of a base.

mutation
Any heritable change in DNA sequence. Compare polymorphism.

multiplexing
A sequencing approach that uses several pooled samples simultaneously, greatly increasing sequencing speed.

mrna
RNA that serves as a template for protein synthesis. See genetic code.

mitosis
The process of nuclear division in cells that produces daughter cells that are genetically identical to each other and to the parent cell.

metaphase
A stage in mitosis or meiosis during which the chromosomes are aligned along the equatorial plane of the cell.

meiosis
The process of two consecutive cell divisions in the diploid progenitors of sex cells. Meiosis results in four rather than two daughter cells, each with a haploid set of chromosomes.

mb
Unit of length for DNA fragments equal to 1 million nucleotides and roughly equal to 1 cM.

marker
An identifiable physical location on a chromosome (e.g., restriction enzyme cutting site, gene) whose inheritance can be monitored. Markers can be expressed regions of DNA (genes) or some segment of DNA with no known coding function but whose pattern of inheritance can be determined. See RFLP, restriction fragment length polymorphism.

macrorestriction map
Map depicting the order of and distance between sites at which restriction enzymes cleave chromosomes.

localize
Determination of the original position (locus) of a gene or other marker on a chromosome.

linkage map
A map of the relative positions of genetic loci on a chromosome, determined on the basis of how often the loci are inherited together. Distance is measured in centimorgans (cM).

library
An unordered collection of clones (i.e., cloned DNA from a particular organism), whose relationship to each other can be established by physical mapping. Compare genomic library, arrayed library.

linkage
The proximity of two or more markers (e.g., genes, RFLP markers) on a chromosome; the closer together the markers are, the lower the probability that they will be separated during DNA repair or replication processes (binary fission in prokaryotes, mitosis or meiosis in eukaryotes), and hence the greater the probability that they will be inherited t...

kb
Unit of length for DNA fragments equal to 1000 nucleotides.

in vitro
Outside a living organism.

karyotype
A photomicrograph of an individuals chromosomes arranged in a standard format showing the number, size, and shape of each chromosome type; used in low- resolution physical mapping to correlate gross chromosomal abnormalities with the characteristics of specific diseases.

introns
The DNA base sequences interrupting the protein- coding sequences of a gene; these sequences are transcribed into RNA but are cut out of the message before it is translated into protein. Compare exons.

interphase
The period in the cell cycle when DNA is replicated in the nucleus; followed by mitosis.

in situ hybridization
Use of a DNA or RNA probe to detect the presence of the complementary DNA sequence in cloned bacterial or cultured eukaryotic cells.

informatics
The study of the application of computer and statistical techniques to the management of information. In genome projects, informatics includes the development of methods to search databases quickly, to analyze DNA sequence information, and to predict protein sequence and structure from DNA sequence data.

hybridization
The process of joining two complementary strands of DNA or one each of DNA and RNA to form a double- stranded molecule.

human genome initiative
Collective name for several projects begun in 1986 by DOE to (1) create an ordered set of DNA segments from known chromosomal locations, (2) develop new computational methods for analyzing genetic map and DNA sequence data, and (3) develop new techniques and instruments for detecting and analyzing DNA. This DOE initiative is now known as the Human ...

human gene therapy
Insertion of normal DNA directly into cells to correct a genetic defect.

homologous chromosomes
A pair of chromosomes containing the same linear gene sequences, each derived from one parent.

homologies
Similarities in DNA or protein sequences between individuals of the same species or among different species.

homeobox
A short stretch of nucleotides whose base sequence is virtually identical in all the genes that contain it. It has been found in many organisms from fruit flies to human beings. In the fruit fly, a homeobox appears to determine when particular groups of genes are expressed during development.

heterozygosity
The presence of different alleles at one or more loci on homologous chromosomes.

haploid
A single set of chromosomes (half the full set of genetic material), present in the egg and sperm cells of animals and in the egg and pollen cells of plants. Human beings have 23 chromosomes in their reproductive cells. Compare diploid.

gene disorder
Hereditary disorder caused by a mutant allele of a single gene (e.g., Duchenne muscular dystrophy, retinoblastoma, sickle cell disease). Compare polygenic disorders.

genomic library
A collection of clones made from a set of randomly generated overlapping DNA fragments representing the entire genome of an organism. Compare library, arrayed library.

genome projects
Research and technology development efforts aimed at mapping and sequencing some or all of the genome of human beings and other organisms.

genome
All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs.

genetics
The study of the patterns of inheritance of specific traits.

genetic engineering technologies
See recombinant DNA technologies.

genetic code
The sequence of nucleotides, coded in triplets (codons) along the mRNA, that determines the sequence of amino acids in protein synthesis. The DNA sequence of a gene can be used to predict the mRNA sequence, and the genetic code can in turn be used to predict the amino acid sequence.

gene product
The biochemical material, either RNA or protein, resulting from expression of a gene. The amount of gene product is used to measure how active a gene is; abnormal amounts can be correlated with disease- causing alleles.

gene mapping
Determination of the relative positions of genes on a DNA molecule (chromosome or plasmid) and of the distance, in linkage units or physical units, between them.

gene families
Groups of closely related genes that make similar products.

gene expression
The process by which a genes coded information is converted into the structures present and operating in the cell. Expressed genes include those that are transcribed into mRNA and then translated into protein and those that are transcribed into RNA but not translated into protein (e.g., transfer and ribosomal RNAs).

gamete
Mature male or female reproductive cell (sperm or ovum) with a haploid set of chromosomes (23 for humans).

flow karyotyping
Use of flow cytometry to analyze and/or separate chromosomes on the basis of their DNA content.

flow cytometry
Analysis of biological material by detection of the light- absorbing or fluorescing properties of cells or subcellular fractions (i.e., chromosomes) passing in a narrow stream through a laser beam. An absorbance or fluorescence profile of the sample is produced. Automated sorting devices, used to fractionate samples, sort successive droplets of the...

fluorescence in situ hybridization
A physical mapping approach that uses fluorescein tags to detect hybridization of probes with metaphase chromosomes and with the less- condensed somatic interphase chromatin.

exonuclease
An enzyme that cleaves nucleotides sequentially from free ends of a linear nucleic acid substrate.

exons
The protein- coding DNA sequences of a gene. Compare introns.

evolutionarily conserved
See conserved sequence.

exogenous dna
DNA originating outside an organism.

eukaryote
Cell or organism with membrane- bound, structurally discrete nucleus and other well- developed subcellular compartments. Eukaryotes include all organisms except viruses, bacteria, and blue- green algae. Compare prokaryote. See chromosomes.

est
Expressed sequence tag. See sequence tagged site.