Genetics M - Q
Terms
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- macromolecule
- a large polymer such as DNA, a protein, or a polysaccharide
- map unit (m.u.)
- the "distance" between two linked gene pairs where 1 percent of the products of meiosis are recombinant; a unit of distance in a linkage map
- mapping function
- a formula expressing the relationship between distance in a linkage map and recombinant frequency
- marker retention
- a technique used in yeast to test the degree of linkage between two mitochondrial mutations
- maternal effect
- the environmental influence of the mother's tissues on the phenotype of the offspring
- maternal inheritance
- a type of uniparental inheritance in which all progeny have the genotype and phenotype of the parent acting as the female
- mating types
- the equivalent in lower organisms of the sexes in higher organisms; the mating types typically differ only physiologically and not in physical form
- matroclinous inheritance
- inheritance in which all offspring have the nucleus-determined phenotype of the mother
- mean
- the arithmetic average
- medium
- any material on (or in) which experimental cultures are grown
- meiocyte
- cell in which meiosis occurs
- meiosis
- two successive nuclear divisions (with corresponding cell divisions) that produce gametes (in animals) or sexual spores (in plants and fungi) having one-half of the genetic material of the original cell
- meiospore
- cell that is one of the products of meiosis in plants
- melting
- denaturation of DNA
- Mendelian ratio
- a ratio of progeny phenotypes reflecting the operation of Mendel's laws
- Mendel's first law
- the two members of a gene pair segregate from each other during meiosis; each gamete has an equal probability of obtaining either member of the gene pair
- Mendel's second law
- the law of independent assortment; unlinked or distantly linked segregating gene pairs assort independently at meiosis
- merozygote
- a partially diploid E. coli cell formed from a complete chromosome (the endogenote) plus a fragment (the exogenote)
- mRNA
- messenger RNA
- Met
- methionine (an amino acid)
- metabolism
- the chemical reactions that occur in a living cell
- metacentric chromosome
- a chromosome having its centromere in the middle
- metaphase
- an intermediate stage of nuclear division when chromosomes align along the equatorial plane of the cell
- midparent value
- the mean of the values of a quantitative phenotype for two specific parents
- minimal medium
- a medium containing only inorganic salts, a carbon source, and water
- missense mutation
- a mutation that alters a codon so that it encodes a different amino acid
- mitochondrion
- a eukaryotic organelle that is the site of ATP synthesis and of the citric acid cycle
- mitosis
- a type of nuclear division (occurring at cell division) that produces two daughter nuclei identical to the parent nucleus
- mitotic crossover
- a crossover resulting from the pairing of homologs in a mitotic diploid
- mode
- the single class in a statistical distribution having the greatest frequency
- modifier gene
- a gene that affects the phenotypic expression of another gene
- molecular genetics
- the study of the molecular processes underlying gene structure and function
- monocistronic mRNA
- an mRNA that codes for one protein
- monoecious plant
- a plant species in which male and female organs are found on the same plant but in different flowers (for example, corn)
- monohybrid cross
- a cross between two individuals identically heterozygous at one gene pair -- for example, Aa X Aa
- monoploid
- a cell having only one chromosome set (usually an aberration), or an organism composed of such cells
- monosomic
- a cell or individual that is basically diploid but that has only one copy of one particular chromosome type and thus has chromosome number 2n - 1
- mosaic
- a chimera; a tissue containing two or more genetically distinct cell types, or an individual composed of such tissues
- messenger RNA (mRNA)
- an RNA molecule transcribed from the DNA of a gene, and from which a protein is translated by the action of ribosomes
- mtDNA
- mitochondrial DNA
- mu phage
- a kind ("species") of phage with properties similar to those of insertion sequences, being able to insert, transpose, inactivate, and cause rearrangements
- multimeric structure
- a structure composed of several identical or different subunits held together by weak bonds
- multiple allelism
- the existence of several known alleles of a gene
- multiple-factor hypothesis
- a hypothesis to explain quantitative variation by assuming the interaction of a large number of genes (polygenes), each with a small additive effect on the character
- multiplicity of infection
- the average number of phage particles that infect a single bacterial cell in a specific experiment
- mutagen
- an agent that is capable of increasing the mutation rate
- mutant
- an organism or cell carrying a mutation
- mutant allele
- an allele differing from the allele found in the standard, or wild-type
- mutant hunt
- the process of accumulating different mutants showing abnormalities in a certain structure or function, as a preparation for mutational dissection of that function
- mutant site
- the damaged or altered area within a mutated gene
- mutation
- the process that produces a gene or a chromosome set differing from the wild-type; the gene or chromosome set that results from such a process
- mutation breeding
- use of mutagens to develop variants that can increase agricultural yield
- mutation event
- the actual occurrence of a mutation in time and space
- mutation frequency
- the frequency of mutants in a population
- mutation rate
- the number of mutation events per gene per unit of time (for example, per cell generation)
- mutational dissection
- the study of the components of a biological function through a study of mutations affecting that function
- muton
- the smallest part of a gene that can be involved in a mutation event; now known to be a nucleotide pair
- myeloma
- a cancer of the bone marrow
- negative assortative mating
- preferential mating between phenotypically unlike partners
- negative control
- regulation mediated by factors that block or turn off transcription
- Neurospora
- a pink mold commonly found growing on old food
- neutral mutation
- a mutation that has no effect on the Darwinian fitness of its carriers; a mutation that has no phenotype effect
- neutral petite
- a petite that produces all wild-type progeny when crossed with wild-type
- nicking
- nuclease action to sever the sugar-phosphate backbone in one DNA strand at one specific site
- nitrocellulose filter
- a type of filter used to hold DNA for hybridization
- nitrogen bases
- purine and pyrimidine
- nondisjunction
- the failure of homologs (at meiosis) or sister chromatids (at mitosis) to separate properly to opposite poles
- nonlinear tetrad
- a tetrad in which the meiotic products are in no particular order
- non-Mendelian ratio
- an unusual ration of progeny phenotypes that does not reflect the simple operation of Mendel's laws; for example, mutant: wild ratios of 3:5, 5:3, 6:2, or 2:6 in tetrads indicate that gene conversion has occurred
- NPD
- nonparental ditype
- nonparental ditype (NPD)
- a tetrad type containing two different genotypes, both of which are recombinant
- nonsense codon
- a codon for which no normal tRNA molecule exists; the presence of a nonsense codon causes termination of translation (the end of the polypeptide chain)
- the three nonsense codons
- amber, ocher, opal
- nonsense mutation
- a mutation that alters a gene so as to produce a nonsense codon
- nonsense suppressor
- a mutation that produces an altered tRNA that will insert an amino acid during translation in response to a nonsense codon
- norm of reaction
- the pattern of phenotypes produced by a given genotype under different environmental conditions
- nuclease
- an enzyme that can degrade DNA by breaking its phosphodiester bonds
- nucleoid
- a DNA mass within a chloroplast or mitochondrion
- nucleolar organizer
- a region or regions of the chromosome set physically associated with the nucleolus and containing rRNA genes
- nucleolus
- an organelle found in the nucleus, containing rRNA and amplified multiple copies of the genes coding for RNA
- nucleoside
- a nitrogen base bound to a sugar molecule
- nucleosome
- a nu body; the basic unit of eukaryotic chromosome structure; a ball of eight histone molecules wrapped about by two coils of DNA
- nucleotide
- a molecule composed of a nitrogen base, a sugar, and a phosphate group; the basic building block of nucleic acids
- nucleotide pair
- a pair of nucleotides (one in each strand of DNA) that are joined by hydrogen bonds
- nucleotide-pair substitution
- the replacement of a specific nucleotide pair by a different pair; often mutagenic
- null allele
- an allele whose effect is either an absence of normal gene product at the molecular level or an absence of normal function at the phenotypic level
- nullisomic
-
a cell or individual with one chromosomal type missing, with a chromosome number such as n - 1 or
2n - 2 - ocher codon
- the codon UAA, a nonsense codon
- octad
- an ascus containing eight ascospores, produced in species in which the tetrad normally undergoes a post-meiotic mitotic division
- oncogene
- a gene that causes cancer
- opal codon
- the codon UGA, a nonsense codon
- open reading frame
- a nucleotide sequence with no stop codons, discovered by sequencing
- operator
- a DNA region at one end of an operon that acts as the binding site for repressor protein
- operon
- a set of adjacent structural genes whose mRNA is synthesized in one piece, plus the adjacent regulatory signals that affect transcription on the structural genes
- ORF
- open reading frame
- open reading frame (ORF)
- generally synonymous with URF
- organelle
- a subcellular structure having a specialized function -- for example, the mitochondrion, the chloroplast, or the spindle apparatus
- origin of replication
- the point of specific sequence at which DNA replication is initiated
- overdominance
- a phenotypic relation in which the phenotypic expression of the heterozygote is greater than that of either homozygote
- palindrome
- a sequence of DNA that is the same when each strand is read in the same direction
- paracentric inversion
- an inversion not involving the centromere
- parental ditype (PD)
- a tetrad type containing two different genotypes, both of which are parental
- particulate inheritance
- the model proposing that genetic information is transmitted from one generation to the next in discrete units ("particles"), so that the character of the offspring is not a smooth blend of essences from the parents
- pathogen
- an organism that causes disease in another organism
- patroclinous inheritance
- inheritance in which all offspring have the nucleus-based phenotype of the father
- pedigree
- a "family tree" drawn with standard genetic symbols, showing inheritance patterns for specific phenotypic characters
- peptide bond
- a bond joining two amino acids
- penetrance
- the proportion of individuals with a specific genotype who manifest that genotype at the phenotype level
- pericentric inversion
- an inversion that involves the centromere
- permissive conditions
- those environmental conditions under which a conditional mutant shows the wild-type phenotype
- petite
- a yeast mutation producing small colonies and altered mitochondrial functions
- cytoplasmic petites
- neural and suppressive petites; the mutation is a deletion in mitochondrial DNA
- segregational petites
- the mutation occurs in nuclear DNA
- Phe
- phenylalanine (an amino acid)
- phenocopy
- an environmentally induced phenotype that resembles the phenotype produced by a mutation
- phenotype
- the form taken by some character or group of characters in a specific individual; the detectable outward manifestations of a specific genotype
- phenotypic sex determination
- sex determination by nongenetic means
- Philadelphia chromosome
- a translocation between the long arms of chromosomes 9 and 22, often found in the white blood cells of patients with chronic myeloid leukemia
- phosphodiester bond
- a bond between a sugar group and a phosphate group
- phosphodiester bonds
- form the sugar-phosphate backbone of DNA
- pilus (plural, pili)
- a conjugation tube; a hollow hairlike appendage of a donor E. coli cell that acts as a bridge for transmission of donor DNA to the recipient cell during conjugation
- plant breeding
- the application of genetic analysis to development of plant lines better suited for human purposes
- plaque
- a clear area on a bacterial lawn, left by lysis of the bacteria through progressive infections by a phage and its descendants
- plasmid
- autonomously replicating extrachromosomal DNA molecule
- plate
- a flat dish used to culture microbes; to spread cells over the surface of solid medium in a flat dish
- pleiotropic mutation
- a mutation that has effects on several different characters
- point mutation
- a mutation that can be mapped to one specific locus
- Poisson distribution
- a mathematical expression giving the probability of observing various numbers of a particular event in a sample when the probability of an event on any one trial is very small, but on which large numbers of trials have been made
- poky
- a slow-growing mitochondrial mutant in Neurospora
- polar gene conversion
- a gradient of conversion frequency along the length of a gene
- polar granules
- granules at the anterior end of the cytoplasm of a Drosophila egg
- polar mutation
- a mutation that affects the transcription or translation of the part of the gene or operon only on one side of the mutant site -- for example, nonsense mutations, frame-shift mutations, and IS-induced mutations
- poly-A tail
- a string of adenine nucleotides added to mRNA after transcription
- polyacrilamide
- a material used to make electrophoretic gels for separation of mixtures of macromolecules
- polycistronic mRNA
- an mRNA that codes for more than one protein
- polymorphism
- the occurrence in a population (or among populations) of several phenotypic forms associated with alleles of one gene or homologs of one chromosome
- polypeptide
- a chain of linked amino acids; a protein
- polyploid
- a cell having three or more chromosome sets, or an organism composed of such cells
- polysaccharide
- a biological polymer composed of sugar subunits--for example, starch or cellulose
- polytene chromosome
- a giant chromosome produced by an endomitotic process in which multiple DNA sets remain bound in a haploid number of chromosomes
- position effect
- used to describe a situation where the phenotypic influence of a gene is altered by changes in the position of the gene within the genome
- position-effect variegation
- variegation caused by the inactivation of a gene in some cells through its abnormal juxtaposition with heterochromatin
- positive assortative mating
- a situation in which like phenotypes mate more commonly than expected by chance
- positive control
- regulation mediated by a protein that is required for the activation of a transcription unit
- primary structures of a protein
- the sequence of amino acids in the polypeptide chain
- Pro
- proline (an amino acid)
- probe
- defined nucleic acid segment that can be used to identify specific DNA molecules bearing the complementary sequence, usually through autoradiography
- product of meiosis
- one of the (usually four) cells formed by the two meiotic divisions
- product rule
- the probability of two independent events occurring simultaneously is the product of the individual probabilities
- proflavin
- a mutagen that tends to produce frame-shift mutations
- prokaryote
- an organism composed of a prokaryotic cell, such as bacteria and blue-green algae
- prokaryotic cell
- a cell having no nuclear membrane and hence no separate nucleus
- promoter
- a regulatory region a short distance from the 5' end of a gene that acts as the binding site for RNA polymerase
- prophage
- a phage "chromosome" inserted as part of the linear structure of the DNA chromosome of a bacterium
- prophase
- the early stage of nuclear division during which chromosomes condense and become visible
- propositus
- in a human pedigree, the individual who first came to the attention of the geneticist
- proto-oncogene
- a gene that, when mutated or otherwise affected, becomes an oncogene
- protoplast
- a plant cell whose wall has been removed
- prototroph
- a strain of organisms that will proliferate on minimal medium
- provirus
- a virus "chromosome" integrated into the DNA of the host cell
- pseudodominance
- the sudden appearance of a recessive phenotype in a pedigree, due to deletion of a masking dominant gene
- pseudogene
- an inactive gene derived from an ancestral active gene
- pulse-chase experiment
- an experiment in which cells are grown in radioactive medium for a brief period and then transferred to nonradioactive medium for a longer period
- pulsed-field gel electrophoresis
- an technique in which gel is subjected to electrical fields alternating between different angles, allowing very large DNA fragments to "snake" through the gel, and hence permit efficient separation of mixtures of such large fragments
- Punnett square
- a grid used as a graphic representation of the progeny zygotes resulting from different gamete fusions in a specific cross
- pure-breeding line or strain
- a group of identical individuals that always produce offspring of the same phenotype when intercrossed
- purine
- a type of nitrogen base
- purine bases in DNA
- adenine and guanine
- pyrimidine bases in DNA
- cytosine and thymine
- quantitative variation
- the existence of a range of phenotypes for a specific character, differing by degree rather than by distinct qualitative differences
- quaternary structure of a protein
- the multimeric constitution of the protein