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199 Cards in this Set
- Front
- Back
R plasmid
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a plasmid containing one or several transposons that bear resistance genes
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random genetic drift
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changes in allele frequency that result because the genes appearing in offspring do not represent a perfectly representative sampling of the parental genes
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random mating
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mating between individuals where the choice of a partner is not influenced by the genotypes (with respect to specific genes under study)
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reading frame
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the codon sequence that is determined by reading nucleotides in groups of three from some specific start codon
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realized heritability
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the ratio of the single-generation progress of selection to the selection differential of the parents
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reannealing
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spontaneous realignment of two single DNA strands to re-form a DNA double helix that had been denatured
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receptor element
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a controlling element that can insert into a gene (making it a mutant) and can also exist (thus making the mutation unstable); both functions under the influence of the regulator element
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recessive allele
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an allele whose phenotype effect is not expressed in a heterozygote
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recessive phenotype
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the phenotype of a homozygote for the recessive allele; the parental phenotype that is not expressed in a heterozygote
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reciprocal translocation
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a translocation in which part of one chromosome is exchanged with a part of a separate nonhomologous chromosome
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recombinant
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an individual or cell with a genotype produced by recombination
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recombinant DNA
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a novel DNA sequence formed by the combination of two nonhomologous DNA molecules
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RF
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recombinant frequency
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recombinant frequency (RF)
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the proportion (or percentage) of recombinant cells or individuals
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recombination (in general)
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any process in a diploid or partially diploid cell that generates new gene or chromosomal combinations not found in that cell or in its progenitors
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recombination (at meiosis)
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the process that generates a haploid product of meiosis whose genotype is different from either of the two haploid genotypes that constituted the meiotic diploid
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recombinational repair
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the repair of a DNA lesion through a process, similar to recombination, that uses recombination enzymes
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recon
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a region of a gene within which there can be crossing-over; now known to be a nucleotide pair
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reduction division
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a nuclear division that produces daughter nuclei each having one-half as many centromeres as the parental nucleus
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regression
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a term coined by Galton for the tendency of the quantitative traits of offspring to be closer to the population mean than are their parents' traits
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regression
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it arises from dominance, gene interaction, and nongenetic influences on traits
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regression coefficient
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the slope of the straight line that most closely relates two correlated variables
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regulatory genes
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genes that are involved in turning on or off the transcription of structural genes
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another name for repetitive DNA
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redundant DNA
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redundant (repetitive) DNA
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DNA sequences that are present in many copies per chromosome set
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replication fork
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the point at which the two strands of DNA are separated to allow replication of each strand
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replicon
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a chromosomal region under the influence of one adjacent replication-initiation locus
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reporter gene
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a gene whose phenotypic expression is easy to monitor
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repressor protein
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a molecule that binds to the operator and prevents transcription of an operon
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repulsion conformation
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two linked heterozygous gene pairs in the arrangement A b/ a B
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resolving power
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the ability of an experimental technique to distinguish between two genetic conditions
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restriction enzyme
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an endonuclease that will recognize specific target nucleotide sequences in DNA and break the DNA chain at those points
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restrictive conditions
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environmental conditions under which a conditional mutant shows the mutant phenotype
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retrovirus
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an RNA virus that replicates by first being converted into double-stranded DNA
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reverse transcriptase
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an enzyme that catalyzes the synthesis of a DNA strand from an RNA template
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reversion
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the production of a wild-type gene from a mutant gene
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RFLP mapping
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a technique in which DNA restriction fragment length polymorphisms are used as reference loci for mapping in relation to known genes or other RFLP loci
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RNA
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ribonucleic acid
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rRNA
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ribosomal RNA
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ribosome
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a complex organelle that catalyzes translation of messenger RNA into an amino-acid sequence
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ribosome
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composed of proteins plus rRNA
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ribonucleic acid (RNA)
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a single-stranded nucleic acid similar to DNA but having ribose sugar rather than deoxyribose sugar and uracil rather than thymine as one of the bases
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RNA polymerase
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an enzyme that catalyzes the synthesis of an RNA strand from a DNA template
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ribosomal RNA (rRNA)
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a class of RNA molecules, coded in the nucleolar organizer, that have an integral (but poorly understood) role in ribosome structure and function
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S
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Svedberg unit
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Svedberg unit (S)
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a unit of sedimentation velocity, commonly used to describe molecular units of various sizes
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satellite
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a terminal section of a chromosome separated from the main body of the chromosome by a narrow constriction
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satellite chromosomes
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chromosomes that seem to be additions to the normal genome
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satellite DNA
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DNA that forms a separate band in a density gradient because of its different nucleotide composition
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scaffold
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the central core of a eukaryotic nuclear chromosome, from which DNA loops extend
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SCE
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sister-chromatid exchange
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sister-chromatid exchange (SCE)
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an event similar to crossing-over that can occur between sister chromatids at mitosis or at meiosis; detected in harlequin chromosomes
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secondary structure of a protein
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a spiral or zigzag arrangement of the polypeptide chain
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second-division segregation pattern
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a pattern of ascospore genotypes for a gene pair showing that the two alleles separate into different nuclei only at the second meiotic division as a result of a crossover between that gene pair and its centromere
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second-site mutation
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the second mutation of a double mutation within a gene
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sector
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an area of tissue whose phenotype is detectably different from the surrounding tissue phenotype
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sector
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an area of tissue whose phenotype is detectably different from the surrounding tissue phenotype
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sedimentation
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the sinking of a molecule under the opposing forces of gravitation and buoyancy
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cytological segregation
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the separation of homologous structures
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genetic segregation
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the production of two separate phenotypes corresponding to two alleles of a gene either in meiotic or mitotic segregation
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segregational petite
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a petite that in a cross with wild-type produces ½ wild-type progeny; caused by a nuclear mutation
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selection coefficient (s)
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the proportional excess or deficiency of a population and the mean of the individuals selected to be parents of the next generation
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selection differential
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the difference between the mean of a population and the mean of the individuals selected to be parents of the next generation
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selection progress
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the difference between the mean of a population and the mean of the offspring in the next generation born to selected parents
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selective neutrality
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a situation in which different alleles of a certain gene confer equal fitness
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selective system
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an experimental technique that enhances the recovery of specific (usually rare) genotypes
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self
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to fertilize eggs with sperms from the same individual
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self-assembly
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the ability of certain multimeric biological structures to assemble from their component parts through random movements of the molecules and formation of weak chemical bonds
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semiconservative replication
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the established model of DNA replication in which each double-stranded molecule is composed of one parental strand and one newly polymerized strand
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semisterility
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the phenotype of individuals heterozygotic for certain types of chromosome aberration; expressed as a reduced number of viable gametes and hence reduced fertility
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senDNA
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an amplified section of mtDNA found in senescent Podospora cultures; circular and plasmid-like in nature
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sex chromosome
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a chromosome whose presence or absence is correlated with the sex of the bearer; a chromosome that plays a role in sex determination
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sex linkage
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the location of a gene on a sex chromosome
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sexduction
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sexual transmission of a donor E. coli chromosomal genes on the fertility factor
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shotgun technique
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cloning a large number of different DNA fragments as a prelude to selecting one particular clone type for intensive study
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shuttle vector
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a vector constructed in such a way that it can replicate in at least two different host species, allowing a DNA segment to be tested or manipulated in several cellular settings
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signal sequence
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the N-terminal sequence of a secreted protein, which is required for transport through the cell membrane
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silent mutation
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mutation in which the function of the protein product of the gene is unaltered
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sister-chromatid exchange (SCE)
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an event similar to crossing-over that can occur between sister chromatids at mitosis or at meiosis; detected in harlequin chromosomes
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SCE
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sister-chromatid exchange
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site-specific recombination
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recombination occurring between two specific sequences that need not be homologous, and mediated by a specific recombination system
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S-9 mix
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a liver-derived supernatant used in the Ames test to activate or inactivate mutagens
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solenoid structure
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the supercoiled arrangement of DNA in eukaryotic nuclear chromosomes
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somatic cell
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a cell that is not destined to become a gamete; a "body cell," whose genes will not be passed on to future generations
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somatic mutation
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a mutation occurring in a somatic cell
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somatic-cell genetics
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asexual genetics, involving study of somatic mutation, assortment, and crossing-over, and of cell fusion
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somatostatin
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a human growth hormone
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SOS repair
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the error-prone process whereby gross structural DNA damage is circumvented by allowing replication to proceed past the damage through imprecise polymerization
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spacer DNA
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repetitive DNA found between genes; its function is unknown
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specialized (restricted) transduction
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the situation in which a particular phage will transduce only specific regions of the bacterial chromosome
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specific-locus test
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a system for detecting recessive mutations in diploids; normal individuals treated with mutagen are mated to testers that ar homozygous for the recessive alleles at a number of specific loci; the progeny are then screened for recessive phenotypes
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spindle
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the set of microtubular fibers that appear to move eukaryotic chromosomes during division
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splicing
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the reaction that removes introns and joins together exons in RNA
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spontaneous mutation
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a mutation occurring in the absence of mutagens, usually due to errors in the normal functioning of cellular enzymes
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spore
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in plants and fungi, the haploid cells produced by meiosis
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spore
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in fungi, somatic cells that are cast off to act either as gametes or as the initial cells for new haploid individuals
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sporophyte
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the diploid sexual-spore-producing generation in the life cycle of plants, i.e. the stage in which meiosis occurs
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stacking
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the packing of the flattish nitrogen bases at the center of the DNA double helix
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staggered cuts
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the cleavage of two opposite strands of duplex DNA at points near one another
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standard deviation
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the square root of the variance
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statistic
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a computed quantity characteristic of a population, such as the mean
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statistical distribution
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the array of frequencies of different quantitative or qualitative classes in a population
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strain
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a pure-breeding lineage, usually of haploid organisms, bacteria, or viruses
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structural gene
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a gene encoding the amino-acid sequence of a protein
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subvital gene
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a gene that causes the death of some proportion (but not all) of the individuals that express it
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sum rule
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the probability that one or the other of two mutually exclusive events will occur is the sum of their individual probabilities
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supercoil
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a closed double-stranded DNA molecule that is twisted on itself
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superinfection
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phage infection of a cell that already harbors a prophage
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supersuppressor
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a mutation that can suppress a variety of other mutations; typically a nonsense suppressor
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suppressive petite
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a petite that in a cross with wild-type produces progeny of which variable non-Mendelian proportions are petite
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suppressor mutation
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a mutation that counteracts the effects of another mutation; maps at a different site than the mutation it counteracts, either within the gene or at a more distant locus
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synapsis
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close pairing of homologs at meiosis
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synaptonemal complex
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a complex structure that unites homologs during the prophase of meiosis
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syncytium
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a single cell with many nuclei
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T
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thymine, or thymidine
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tandem duplication
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adjacent identical chromosome segments
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tautomeric shift
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the spontaneous isomerization of a nitrogen base to an alternative hydrogen-bonding condition, possibly resulting in a mutation
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T-DNA
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a portion of the Ti plasmid that is inserted into the genome of the host plant cell
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telocentric chromosome
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a chromosome having the centromere at one end
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telophase
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the late stage of nuclear division when daughter nuclei re-form
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temperate phage
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a phage that can become a prophage
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temperature-sensitive mutation
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a conditional mutation that produces the mutant phenotype in one temperature range and the wild-type phenotype in another temperature range
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template
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a molecular "mold" that shapes the structure or sequence of another molecule
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teratogen
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an agent that interferes with normal development
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teratoma
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a tumor composed of a chaotic array of different tissue types
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terminal redundancy
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in phage, a linear DNA molecule with single-stranded ends that are longer than is necessary to close the DNA circle
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tertiary structure of a protein
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the folding or coiling of the secondary structure to form a globular molecule
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testcross
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a cross of an individual of unknown genotype or a heterozygote (or a multiple heterozygote) to a tester individual
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tester
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an individual homozygous for one or more recessive alleles; used in a testcross
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testicular feminization
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the creation of an apparent female phenotype in an XY individual as a result of an X-linked mutation
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tetrad
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four homologous chromatids in a bundle in the first meiotic prophase and metaphase
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tetrad
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the four haploid product cells from a single meiosis
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tetrad analysis
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the use of tetrads to study the behavior of chromosomes and genes during meiosis
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tetraparental mouse
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a mouse that develops from an embryo created by the experimental fusion of two separate blastulas
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tetraploid
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a cell having four chromosome sets; an organism composed of such cells
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tetratype (T)
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a tetrad type containing four different genotypes, two parental two and two recombinant
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Thr
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threonine (an amino acid)
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three-point testcross
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a testcross involving one parent with three heterozygous gene pairs
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thymidine
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the nucleoside having thymine as its base
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thymine dimer
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a pair of chemically bonded adjacent thymine bases in DNA; the cellular processes that repair this lesion often make errors that create mutations
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Ti plasmid
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a circular plasmid of Agrobacterium tumifaciens that enables the bacterium to infect plant cells and produce a tumor (crown gall tumor)
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totipotency
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the ability of a cell to proceed through all the stages of development and thus produce a normal adult
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trans conformation
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in a heterozygote involving two mutant sites within a gene or gene cluster
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transcription
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the synthesis of RNA using a DNA template
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transdetermination
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a specific change in the fate of an imaginal disk that can occur when the disk is cultured
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transduction
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the movement of genes from a bacterial donor to a bacterial recipient using a phage as the vector
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transformation (first definition)
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the directed modification of a genome by the external application of DNA from a cell of different genotype
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transformation (second definition)
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conversion of normal higher eukaryotic cells in tissue culture to a cancer-like state of uncontrolled division
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transgenic organism
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one whose genome has been modified by externally-applied new DNA
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transient diploid
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the stage of the life cycle of predominantly haploid fungi (and algae) during which meiosis occurs
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transition
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a type of nucleotide-pair substitution involving the replacement of a purine with another purine, or of a pyrimidine with another pyrimidine
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transition
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for example, GC -> AT
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translation
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the ribosome-mediated production of a polypeptide chain whose amino-acid sequence is derived from the codon sequence of an mRNA molecule
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translocation
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the relocation of a chromosomal segment in a different position in the genome
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transmission genetics
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the study of the mechanisms involved in the passage of a gene from one generation to the next
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transposable genetic element
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a general term for any genetic unit that can insert into a chromosome, exit, and relocate; includes insertion sequences, transposons, some phages, and controlling elements
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transposon
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a mobile piece of DNA that is flanked by terminal repeat sequences and typically bears genes coding for transposition functions
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transversion
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a type of nucleotide-pair substitution involving the replacement of a purine with a pyrimidine, or vice versa
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transversion
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for example, GC -> TA
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triplet
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the three nucleotide pairs that compose a codon
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triploid
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a cell having three chromosome sets, or an organism composed of such cells
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trisomic
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basically, a diploid with an extra chromosome of one type, producing a chromosome number of the form 2n + 1
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tritium
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a radioactive isotope of hydrogen
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tRNA
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transfer RNA
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transfer RNA (tRNA)
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a class of small RNA molecules that bear specific amino acids to the ribosome during translation
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Trp
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tryptophan (an amino acid)
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truncation selection
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a breeding technique in which individuals in whom quantitative expression of a phenotype is above or below a certain value are selected as parents for the next generation
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Turner's syndrome
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an abnormal human female phenotype produced by the presence of only one X chromosome (XO)
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twin spot
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a pair of mutant sectors within wild-type tissue, produced by a mitotic crossover in an individual of appropriate heterozygous genotypye
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2 µ ( 2 micron) plasmid
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a naturally-occurring extragenomic circular DNA molecule; engineered to form the basis for several types of gene vectors in yeast
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found in some yeast cells with a circumferance of 2µ
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2µ (2 micron) plasmid
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Tyr
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tyrosine (an amino acid)
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unequal crossover
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a crossover between homologs that are not perfectly aligned
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uniparental inheritance
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the transmission of certain phenotypes from one parental type to all the progeny; such inheritance is generally produced by organelle genes
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unstable mutation
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a mutation that has a high frequency of reversion; a mutation caused by the insertion of a controlling element, whose subsequent exit produces a reversion
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uracil
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a pyrimidine base that appears in RNA in place of thymine found in DNA
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URF (unassigned reading frame)
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a DNA region, identified by nucleotide sequencing studies, that has an initiation and a termination codon, and therefore presumably represents a gene, but for which no phenotype or function is known
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uridine
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the nucleoside having uracil as its base
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Val
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valine (an amino acid)
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variable
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a property that may have different values in various cases
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variance
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a measure of the variation around the central class of a distribution; the average squared deviation of the observations from their mean value
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variable region
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a region in an immunoglobin molecule that shows many sequence differences between antibodies of different specificities
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variable region
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the part of the antibody that binds to the antigen
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variant
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an individual organism that is recognizably different from an arbitrary standard type in that species
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variate
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a specific numerical value of a variable
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variation
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the differences among parents and their offspring or among individuals in a population
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variegation
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the occurrence within a tissue of sectors with differing phenotypes
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vector
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in cloning, the plasmid or phage chromosome used to carry the cloned DNA segment
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viability
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the probability that a fertilized egg will survive and develop into an adult organism
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virulent phage
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a phage that cannot become a prophage; infection by such a phage always leads to lysis of the host cell
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wild-type
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the genotype or phenotype that is found in nature or in the standard laboratory stock for a given organism
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wobble
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the ability of certain bases at the third position of an anticodon in tRNA to form hydrogen bonds in various ways, causing alignment with several possible codons
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X linkage
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the presence of a gene on the X chromosome but not on the Y
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X-and-Y linkage
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the presence of a gene on both the X and Y chromosomes (rare)
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X-ray crystallography
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a technique for deducing molecular structure by aiming a beam of X rays at a crystal of the test compound and measuring the scatter of rays
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Y linkage
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the presence of a gene on the Y chromosome but not on the X (rare)
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zygote
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the cell formed by the fusion of an egg and a sperm
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zygote
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the unique diploid cell that will divide mitotically to create a differentiated diploid organism
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zygotic induction
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the sudden release of a lysogenic phage from an Hfr chromosome when the prophage enters the F¯ cell, and the subsequent lysis of the recipient cell
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