夏 Back to bto home page Jump to Terms beginning with A DEF= LMNO P-RS TUy J Co-Cz G K 2μ(2 micron) plasmid A naturally occurring extragenomic (not part of the genome) circular DNA molecule found in some yeast cells, with a circumference of 2u. Engineered to form the basis for veral types of gene vectors in yeast Adenine or adenosine A(aminoacyl) site The site on the ribosome occupied by an aminoacvl-trna just prior to peptide bond formation A form dna The form of DNA at high humidity; it has tilted base pairs and more base pairs per turn han does b dna abortive transduction The failure of a transducing DNA segment to be incorporated into the recipient acentric chromosome chromosome having no centromere acentric fragment A chromosomal piece without a centromere achondroplasia A type of dwarfism in humans inherited as an autosomal dominant phenoty acrocentric chromosome a chromosome whose centromere lies very near one end. See also metacentric activation energy(delta) Energy needed to initiate a chemical reaction
¤ B a ck t o B TO h ome p age Jump to Terms beginning with: A B Ca-Cn Co-Cz D E F G H I J K L M N O P Q R S T U V W X Y Z 2µ (2 micron) plasmid A naturally occurring extragenomic (not part of the genome) circular DNA molecule found in some yeast cells, with a circumference of 2µ. Engineered to form the basis for several types of gene vectors in yeast. A Adenine or adenosine. A (aminoacyl) site The site on the ribosome occupied by an aminoacyl-tRNA just prior to peptide bond formation. A form DNA The form of DNA at high humidity; it has tilted base pairs and more base pairs per turn than does B DNA. abortive transduction The failure of a transducing DNA segment to be incorporated into the recipient chromosome. acentric chromosome A chromosome having no centromere. acentric fragment A chromosomal piece without a centromere. achondroplasia A type of dwarfism in humans inherited as an autosomal dominant phenotype. acrocentric chromosome A chromosome whose centromere lies very near one end. See also metacentric chromosome activation energy (deltaG) Energy needed to initiate a chemical reaction
active site The part of a protein that must be maintained in a specific shape if the protein is to be functional, for example, the part to which the substrate binds in an enzyme. The part of an enzyme where the actual enzymatic function is performed adaptation In the evolutionary sense, some heritable feature of an individuals phenotype that improves its chances of survival and reproduction in the existing environment adaptive landscape The surface plotted in a three-dimensional graph; with all possible combinations of allele frequencies for different loci plotted in the plane; and mean fitness for each combination plotted in the third dimension adaptive peak a high point(perhaps one of several)on an adaptive landscape; selection tends to drive the genotype composition of the population toward a combination corresponding to an adaptive surface See adaptive landscape adaptive value See fitness additive genetic variance Genetic variance associated with the average effects of substituting one allele for another additive model A mechanism of quantitative inheritance in which alleles at different loci either add a fixed amount to the phenotype or add nothing adenine A purine base that pairs with thymine in the dNa double helix. See purines adenosine The nucleoside containing adenine as its base adenosine triphosphate See atp adjacent segregation In a reciprocal translocation heterozygote during meiosis the segregation of a translocated
active site The part of a protein that must be maintained in a specific shape if the protein is to be functional, for example, the part to which the substrate binds in an enzyme. The part of an enzyme where the actual enzymatic function is performed. adaptation In the evolutionary sense, some heritable feature of an individual's phenotype that improves its chances of survival and reproduction in the existing environment. adaptive landscape The surface plotted in a three-dimensional graph; with all possible combinations of allele frequencies for different loci plotted in the plane; and mean fitness for each combination plotted in the third dimension. adaptive peak A high point (perhaps one of several) on an adaptive landscape; selection tends to drive the genotype composition of the population toward a combination corresponding to an adaptive peak. adaptive surface See adaptive landscape. adaptive value See fitness. additive genetic variance Genetic variance associated with the average effects of substituting one allele for another. additive model A mechanism of quantitative inheritance in which alleles at different loci either add a fixed amount to the phenotype or add nothing. adenine A purine base that pairs with thymine in the DNA double helix. See purines. adenosine The nucleoside containing adenine as its base. adenosine triphosphate See ATP. adjacent segregation In a reciprocal translocation heterozygote during meiosis the segregation of a translocated
and a normal chromosome together, giving unbalanced gametes with duplications and deficiencies leading to non-viable zygotes. Adjacent segregation is of two kinds depending on whether non-homologous (adjacent-1)or homologous (adjacent-2) centromeres segregate together. Adiacent-l segregation is the usual type of adjacent gregation, adjacent-2 segregation is rare adjacent-l segregation segregation of non-homologous centromeres during meiosis in a reciprocal translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced. See alternate segregation and adiacent-2 segregation adjacent-2 segregation segregation of homologous centromeres during meiosis in a translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced. See alternate segregation and adiacent-I segregation ADP Adenosine diphosphate affected Individuals in a pedigree that exhibit the specific phenotype under study Ala Alanine(an amino acid) albino a pigmentless white phenotype, determined by a mutation in a gene coding for a pigment-synthesizing enzyme alkylating agent A chemical agent that can add alkyl groups(for example, ethyl or methyl groups)to another molecule; many mutagens act through alkylation allele Alternative form of a gene. One of the different forms of a gene that can exist at a single allele frequency Often called gene frequency. A measure of how common an allele is in a population; the proportion of all alleles at one gene locus that are of one specific type in a population allelic exclusion a process whereby only one immunoglobulin light chain and one heavy chain gene are transcribed in any one cell; the other genes are repressed
and a normal chromosome together, giving unbalanced gametes with duplications and deficiencies leading to non-viable zygotes. Adjacent segregation is of two kinds depending on whether non-homologous (adjacent-1) or homologous (adjacent-2) centromeres segregate together. Adjacent-1 segregation is the usual type of adjacent segregation, adjacent-2 segregation is rare. adjacent-1 segregation segregation of non-homologous centromeres during meiosis in a reciprocal translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced. See alternate segregation and adjacent-2 segregation. adjacent-2 segregation segregation of homologous centromeres during meiosis in a translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced. See alternate segregation and adjacent-1 segregation. ADP Adenosine diphosphate. affected Individuals in a pedigree that exhibit the specific phenotype under study. Ala Alanine (an amino acid). albino A pigmentless white phenotype, determined by a mutation in a gene coding for a pigment-synthesizing enzyme. alkylating agent A chemical agent that can add alkyl groups (for example, ethyl or methyl groups) to another molecule; many mutagens act through alkylation. allele Alternative form of a gene. One of the different forms of a gene that can exist at a single locus. allele frequency Often called gene frequency. A measure of how common an allele is in a population; the proportion of all alleles at one gene locus that are of one specific type in a population. allelic exclusion A process whereby only one immunoglobulin light chain and one heavy chain gene are transcribed in any one cell; the other genes are repressed
allopatric speciation speciation in which the evolution of reproductive isolating mechanisms occurs during physical separation of the populations allopolyploid polyploid produced by the hybridization of two species. See amphidiploid allosteric protein a protein whose shape is changed when it binds a particular molecule. In the new shape the protein's ability to react to a second molecule is altered allosteric transition A change from one conformation of a protein to another allotype The protein product (or the result of its activity of an allele which may be detected as an antigen in another member of the same species (eg histocompatibility antigens, immunoglobulins), obeying the rules of simple Mendelian inheritance allozygosity homozygosity in which the two alleles are alike but unrelated. See autozygosity allozyme Form of an enzvme that differs in amino acid sequence, as shown by electrophoretic mobility or some other property, from other forms of the same enzyme and is encoded by one allele at a single locus. See isozymes alternate segregation At meiosis in a reciprocal translocation heterozygote, the passage(segregation) of both normal chromosomes to one pole and both translocated chromosomes to the other pole giving genetically balanced gametes. Segregation of centromeres during meiosis in a reciprocal translocation heterozygote such that genetically balanced gametes are alternation of generations The alternation of gametophyte and sporophyte stages in the life cycle of a plant alternative splicing Various ways of splicing out introns in eukaryotic pre-mRNAs resulting in one gene producing several different mRNAs and protein products altruism a form of behaviour in which an individual risks lowering its fitness for the benefit of
allopatric speciation speciation in which the evolution of reproductive isolating mechanisms occurs during physical separation of the populations. allopolyploid polyploid produced by the hybridization of two species. See amphidiploid. allosteric protein A protein whose shape is changed when it binds a particular molecule. In the new shape the protein's ability to react to a second molecule is altered. allosteric transition A change from one conformation of a protein to another. allotype The protein product (or the result of its activity) of an allele which may be detected as an antigen in another member of the same species.(eg histocompatibility antigens, immunoglobulins), obeying the rules of simple Mendelian inheritance. allozygosity homozygosity in which the two alleles are alike but unrelated. See autozygosity. allozyme Form of an enzyme that differs in amino acid sequence, as shown by electrophoretic mobility or some other property, from other forms of the same enzyme and is encoded by one allele at a single locus. See isozymes. alternate segregation At meiosis in a reciprocal translocation heterozygote, the passage (segregation) of both normal chromosomes to one pole and both translocated chromosomes to the other pole, giving genetically balanced gametes. Segregation of centromeres during meiosis in a reciprocal translocation heterozygote such that genetically balanced gametes are produced. alternation of generations The alternation of gametophyte and sporophyte stages in the life cycle of a plant. alternative splicing Various ways of splicing out introns in eukaryotic pre-mRNAs resulting in one gene producing several different mRNAs and protein products. altruism A form of behaviour in which an individual risks lowering its fitness for the benefit of
another Alu famil a dispersed intermediately repetitive DNA sequence found in the human genome in about three hundred thousand copies. The sequence is about 300 bp long. The name Alu comes from the restriction endonuclease alul that cleaves it amber codon The codon UAG, a nonsense codon amber suppressor a mutant allele coding for a tRNa whose anticodon is altered in such a way that the suppressor tRNA inserts an amino acid at an amber codon in translation suppressing (preventing)termination Ames test A widely used test to detect possible chemical carcinogens based on mutagenicity in the bacterium Salmonella amino acid The basic building block of proteins (or polypeptides). Containing a basic amino(NH2) group, an acidic carboxyl( COOH) group and a side chain(R-of a number of different kinds)attached to an alpha carbon atom. Thus NH2-C-CO0H aminoacyl-tRNA Transfer RNA (tRNA) molecule with its cognate amino acid attached aminoacyl-tRNA synthetase enzyme that attaches an amino acid to its cognate tRNA(S) amniocentesis a technique for testing the genotype of an embryo or fetus in utero with minimal risk to the mother or the child amorph A mutant showing the complete lack of some normal substance or structure AMP Adenosine monophosphate
another. Alu family A dispersed intermediately repetitive DNA sequence found in the human genome in about three hundred thousand copies. The sequence is about 300 bp long. The name Alu comes from the restriction endonuclease AluIthat cleaves it. amber codon The codon UAG, a nonsense codon. amber suppressor A mutant allele coding for a tRNA whose anticodon is altered in such a way that the suppressor tRNA inserts an amino acid at an amber codon in translation suppressing (preventing) termination. Ames test A widely used test to detect possible chemical carcinogens; based on mutagenicity in the bacterium Salmonella. amino acid The basic building block of proteins (or polypeptides). Containing a basic amino (NH2) group, an acidic carboxyl (COOH) group and a side chain (R - of a number of different kinds) attached to an alpha carbon atom. Thus: R | NH2-C-COOH | H aminoacyl-tRNA Transfer RNA (tRNA) molecule with its cognate amino acid attached. aminoacyl-tRNA synthetase enzyme that attaches an amino acid to its cognate tRNA(s). amniocentesis A technique for testing the genotype of an embryo or fetus in utero with minimal risk to the mother or the child. amorph A mutant showing the complete lack of some normal substance or structure. AMP Adenosine monophosphate