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67-570: The chemical is an alkylating agent, and acts by transferring the ethyl group of ENU to nucleobases (usually thymine ) in nucleic acids . Its main targets are the spermatogonial stem cells , from which mature sperm are derived. Bill Russell (1951) created a landmark in the field of mouse genetics by creating a specifically designed mouse strain, the T (test) stock that was used in genetic screens for testing mutagens such as radiations and chemicals. The T -stock mouse harbors 7 recessive, viable mutations affecting easily recognizable traits. At

134-500: A carbonyl group . Nucleophilic alkylating agents can displace halide substituents on a carbon atom through the SN2 mechanism. With a catalyst , they also alkylate alkyl and aryl halides, as exemplified by Suzuki couplings . The SN2 mechanism is not available for aryl substituents, where the trajectory to attack the carbon atom would be inside the ring. Thus, only reactions catalyzed by organometallic catalysts are possible. C-alkylation

201-486: A chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation , a free radical , a carbanion , or a carbene (or their equivalents). Alkylating agents are reagents for effecting alkylation. Alkyl groups can also be removed in a process known as dealkylation . Alkylating agents are often classified according to their nucleophilic or electrophilic character. In oil refining contexts, alkylation refers to

268-520: A balancer are crossed with each other. Offspring that carry the balancer, identified by the dominant marker, can be crossed with littermates. Any such cross that does not produce marker-negative animals is likely the result of a recessive lethal mutation in the non-balancer chromosome. Of course, only the genomic interval covered by the inversions in the balancer can be screened in this way, with recessive lethal mutations in other intervals and on other chromosomes being lost. Balancer chromosomes are named for

335-402: A balancer. In this capacity, balancers are crucial for genetics research on model organisms such as Drosophila melanogaster , the common fruit fly, for which stocks cannot be archived (e.g. frozen). They can also be used in forward genetics screens to specifically identify recessive lethal (or sterile) mutations. For that reason, balancers are also used in other model organisms, most notably

402-444: A constant line. They achieved this by using the FLP recombinase gene, isolated from yeast, which causes large chromosomal inversions . Through trial and error they found that the chromosomes could be recombined such that each had the recessive mutation while the other half contained half of a balancer chromosome with a physical marker and a lethal recessive. The other homolog did not contain

469-638: A curly coat and are discarded. The ENU mutant + rex mutant mice are discarded in order to prevent recombination between those two chromosomes during the next breeding step, which is generating homozygous mutants. Mice that are compound heterozygotes for the balancer and the ENU-induced mutation are brother-sister mated to obtain homozygotes for the ENU-induced mutation in G 3 . Genome-wide screens are most often useful for studying genetic diseases in which multiple genetic and biochemical pathways may be involved. Thus with this approach, candidate genes or regions across

536-412: A deletion of the region of interest. The G 1 progeny are compound heterozygotes for the ENU-induced mutation (Figure 4). Also, they are haploid with respect to the genes in the deleted region and thus loss-of-function or gain-of-function due to the ENU-induced mutation is expressed dominantly. Thus deletion screens have an advantage over other recessive screens due to the identification of the mutation in

603-455: A different strategy is used to identify the mutation. An ENU-treated male is crossed with a wild type female. From the pool of G 1 individuals, a heterozygous male is crossed to a female carrying the mutant allele ( a ). If the G 2 progeny are infertile or non-viable, they can be recovered again from the G 1 male. Deletions on chromosomes can be spontaneous or induced. In this screen, ENU-treated males are crossed to females homozygous for

670-531: A dominant modifier screen using ENU-induced mice to identify modifiers of the Notch signaling pathway. Delta 1 is a ligand for the Notch receptor. A homozygous loss-of-function of Delta 1 ( Dll1 ) is embryonically lethal. ENU-treated mice were crossed to Dll1 heterozygotes. 35 mutant lines were generated in G 1 of which 7 revealed modifiers of the Notch signaling pathway. In the case of genetic diseases involving multiple genes, mutations in multiple genes contributes to

737-509: A double-stranded state; i.e. if RNA remains in a double-stranded state, then the RNAi mechanism of gene silencing is effectively disabled. The authors speculated that this response was an evolutionary trend toward a redundant immune response against RNA viruses. If one cell is already undergoing cell death to attempt to stop the spread of a virus, then the RNAi immune response has been ineffective. This causes another immune response that attempts to stop

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804-567: A laboratory scale the Friedel–Crafts reaction uses alkyl halides , as these are often easier to handle than their corresponding alkenes, which tend to be gasses. The reaction is catalysed by aluminium trichloride . This approach is rarely used industrially as alkyl halides are more expensive than alkenes. N-, P-, and S-alkylation are important processes for the formation of carbon-nitrogen, carbon-phosphorus, and carbon-sulfur bonds, Amines are readily alkylated. The rate of alkylation follows

871-426: A male mouse with ENU. This is followed by systematic phenotypic analysis of the progeny. The progeny are assessed for behavioral, physiological or dysmorphological changes. The abnormal phenotype is identified. Identification of the candidate gene is then achieved by positional cloning of the mutant mice with the phenotype of interest. ENU is used as a genetic tool by designing a variety of genetic screens suitable to

938-401: A mixture of propene and butene ) in the presence of a Brønsted acid catalyst, which can include solid acids (zeolites). The catalyst protonates the alkenes (propene, butene) to produce carbocations , which alkylate isobutane. The product, called "alkylate", is composed of a mixture of high- octane , branched-chain paraffinic hydrocarbons (mostly isoheptane and isooctane ). Alkylate is

1005-412: A mutant [e.g. s / s mutant male] to a wild type female [ + / + ]). Thus with any progeny carrying a mutation induced by radiation at one of the 7 loci, would exhibit the mutant phenotype in the first generation itself. This approach, the specific locus test (SLT) allowed Russell to study a wide range of specific mutations and to calculate the mutation rates induced by radiations. In addition to studying

1072-404: A new covalent bond between the alkyl group and the electrophile. The counterion, which is a cation such as lithium, can be removed and washed away in the work-up . Examples include the use of organometallic compounds such as Grignard (organomagnesium) , organolithium , organocopper , and organosodium reagents. These compounds typically can add to an electron-deficient carbon atom such as at

1139-534: A particular alkylation of isobutane with olefins . For upgrading of petroleum , alkylation produces a premium blending stock for gasoline. In medicine, alkylation of DNA is used in chemotherapy to damage the DNA of cancer cells. Alkylation is accomplished with the class of drugs called alkylating antineoplastic agents . Nucleophilic alkylating agents deliver the equivalent of an alkyl anion ( carbanion ). The formal "alkyl anion" attacks an electrophile , forming

1206-431: A premium gasoline blending stock because it has exceptional antiknock properties and is clean burning. Alkylate is also a key component of avgas . By combining fluid catalytic cracking , polymerization, and alkylation, refineries can obtain a gasoline yield of 70 percent. The widespread use of sulfuric acid and hydrofluoric acid in refineries poses significant environmental risks. Ionic liquids are used in place of

1273-528: A sensitized screen of mouse mutants predisposed to Diabetic nephropathy. Mice were treated with ENU on a sensitized background of type-1 diabetes. These diabetic mice had a dominant Akita mutation in the insulin-2 gene ( Ins2 ). These mice developed albuminuria, a phenotype that was not observed in the non-diabetic offsprings. Generally speaking, ENU is fairly unstable, which makes it easier to inactivate when used as an experimental mutagen, compared to moderately more stable mutagens like EMS . Pure crystalline ENU

1340-595: Is a process for the formation of carbon-carbon bonds. The largest example of this takes place in the alkylation units of petrochemical plants, which convert low-molecular-weight alkenes into high octane gasoline components. Electron-rich species such as phenols are also commonly alkylated to produce a variety of products; examples include linear alkylbenzenes used in the production of surfactants like LAS , or butylated phenols like BHT , which are used as antioxidants . This can be achieved using either acid catalysts like Amberlyst , or Lewis acids like aluminium. On

1407-516: Is a region which prevents recombination between homologous chromosomes during meiosis. This is possible due to the presence of an inverted region or a series of inversions. Balancer chromosome was primarily used for studies in Drosophila melanogaster genetics. Monica Justice et al. (2009) efficiently carried out a balancer screen using a balancer chromosome constructed by Allan Bradley et al. on mouse chromosome 11. In this screen, an ENU-induced male

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1474-433: Is crossed with a female heterozygous for the balancer chromosome. The mice carrying the balancer chromosome have yellow ears and tail. The G 1 heterozygotes are (Figure 5) are crossed to females carrying the rex mutation ( Rex in figure 5), which confers a curly coat. In G 2 , homozygotes for the balancer are non-viable and are not recovered. Mice carrying the rex mutation trans to the balancer or ENU-induced mutation have

1541-530: Is explored in the paper "The Autosomal Flp-Dfs Technique for Generating Germline Mosaics in Drosophila Melanogaster" , which showed for the first time that it is possible to screen for a recessive mutation that only shows a phenotype when homozygous. Using old balancer chromosome methods, genetic screening only allowed for the selection of heterozygous dominant mutations. This experiment uses clonal screening to detect homozygous individuals and keep them in

1608-405: Is in strong linkage disequilibrium with it), recombination resulting in a wild-type chromosome is very unlikely, regardless of recombination suppressive inversions. In addition to simply maintaining an isolated recessive lethal (or sterile) mutation, balancer chromosomes are also useful in forward genetic screens to identify such mutations. In such screens randomly mutagenized organisms carrying

1675-521: Is intermediate in electrophilicity. Diazomethane is a popular methylating agent in the laboratory, but it is too hazardous (explosive gas with a high acute toxicity) to be employed on an industrial scale without special precautions. Use of diazomethane has been significantly reduced by the introduction of the safer and equivalent reagent trimethylsilyldiazomethane . Electrophilic, soluble alkylating agents are often toxic and carcinogenic, due to their tendency to alkylate DNA. This mechanism of toxicity

1742-563: Is one step in the Cativa process for the synthesis of acetic acid from methyl iodide . Many cross coupling reactions proceed via oxidative addition as well. Electrophilic alkylating agents deliver the equivalent of an alkyl cation . Alkyl halides are typical alkylating agents. Trimethyloxonium tetrafluoroborate and triethyloxonium tetrafluoroborate are particularly strong electrophiles due to their overt positive charge and an inert leaving group (dimethyl or diethyl ether). Dimethyl sulfate

1809-474: Is relevant to the function of anti-cancer drugs in the form of alkylating antineoplastic agents . Some chemical weapons such as mustard gas (sulfide of dichloroethyl) function as alkylating agents. Alkylated DNA either does not coil or uncoil properly, or cannot be processed by information-decoding enzymes. Electrophilic alkylation uses Lewis acids and Brønsted acids , sometimes both. Classically, Lewis acids, e.g., aluminium trichloride , are employed when

1876-542: Is said to be "double-balanced" if it is heterozygous for two different balancer chromosomes (for example, TM6, Tb/TM3, Ser ) on one chromosome and a homozygous-lethal, heterozygous-visible mutant on the other, wild-type chromosome (for example, D/TM3, Ser ). Most balancer chromosomes also carry a recessive allele such as the "ebony" mutation that is only manifest in these stocks with two balancer chromosomes. Such stocks are often used to provide sources of easily traceable traits when breeding two different lines together, so that

1943-399: Is sensitive to light and moisture, so should be stored at in cold and dry conditions, and freshly prepared into solutions when needed. In aqueous solutions, ENU rapidly degrades at a basic pH, and protocols call for inactivation of ENU solutions with an equal volume of 0.1M KOH for 24 hours, with or without ambient light exposure to supplement inactivation. Alkylation Alkylation is

2010-421: Is then followed by an M for "multiply inverted". The M is followed by a number to distinguish balancers of the same chromosome. Additionally, the genetic marker or markers within the balancer are listed after the name and separated by a comma. Generally, mutations with easily observable dominant phenotypic traits that are often homozygous lethal are used to ensure that all progeny are heterozygous. For example,

2077-479: The Base Excision Repair (BER) pathway. Several commodity chemicals are produced by alkylation. Included are several fundamental benzene-based feedstocks such as ethylbenzene (precursor to styrene ), cumene (precursor to phenol and acetone ), linear alkylbenzene sulfonates (for detergents). In a conventional oil refinery , isobutane is alkylated with low-molecular-weight alkenes (primarily

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2144-474: The Oak Ridge National Laboratory , Russell's initial goal was to determine the rate of inheritable gene mutations in the germ line induced by radiations. Thus he decided to use T -stock mice in order to define how often a set of loci could be mutated with radiations. Since the mutations in the T -stock mouse were recessive , the progeny would have a wild type phenotype (as a result of crossing

2211-717: The Department of Neurobiology and Physiology at Northwestern University, Illinois, USA; the Oak Ridge National Laboratory, Tennessee, USA; the Medical Research Council (MRC) Harwell, Oxfordshire, United Kingdom; the Department of Genetics at The Scripps Research Institute, California, USA; the Mouse Mutagenesis Center for Developmental Defects at Baylor College of Medicine, Texas, USA; and others. A modifier such as an enhancer or suppressor can alter

2278-663: The G 1 males in two ways: A number of organizations around the world are performing genome-wide mutagenesis screens using ENU. Some of them include the Institute of Experimental Genetics at the German Research Center for Environmental Health (GSF), Munich, Germany; The Jackson Laboratory, Maine, USA; the Australian Phenomics Facility at the Australian National University, Canberra, Australia;

2345-403: The G 1 progeny itself. Rinchik et al . performed a deletion screen and complementation analysis and were able to isolate 11 independent recessive loci, which were grouped into seven complementation groups on chromosome 7, a region surrounding the albino ( Tyr ) gene and the pink-eyed dilution ( p ) gene. A chromosome carrying a balancer region is termed as a balancer chromosome . A balancer

2412-464: The SLT. However, DEN needs to be enzymatically converted into an alkylating agent in order to be mutagenic and probably this enzymatic activation was not sufficient in mammals. This could be illustrated by the extremely low mutation rate in mice given by DEN (3 in 60,179 offspring). To overcome this problem, a new mutagen, N -ethyl N -nitrosourea (ENU), an alkylating agent, which does not need to be metabolised,

2479-403: The adults into which they develop) are then screened for mutations. When a phenotype of interest is observed, the line expressing the mutation is crossed with another line containing balancer chromosomes in order to maintain their lineage. In one instance, balancers were used to genetically screen a population of Caenorhabditis elegans . By this point in time, scientists had already realized

2546-600: The alkyl halide are used. Brønsted acids are used when alkylating with olefins. Typical catalysts are zeolites, i.e. solid acid catalysts, and sulfuric acid. Silicotungstic acid is used to manufacture ethyl acetate by the alkylation of acetic acid by ethylene : Alkylation in biology causes DNA damage . It is the transfer of alkyl groups to the nitrogenous bases . It is caused by alkylating agents such as EMS (Ethyl Methyl Sulphonate). Bifunctional alkyl groups which have two alkyl groups in them cause cross linking in DNA. Alkylation damaged ring nitrogen bases are repaired via

2613-923: The balancer and the homolog containing the mutated allele may also result in the de novo creation of a wild-type chromosome. To suppress recombination, balancers usually harbor multiple, nested chromosomal inversions so that synapsis between the homologous chromosomes is disrupted. If crossing over does occur, it is often unbalanced, with each resulting chromatid lacking some genes and carrying two copies of others. The process can also lead to dicentric or acentric chromosomes (chromosomes with two centromeres or no centromere), which are inherently unstable and usually end up breaking up and mutating or being lost during subsequent mitosis. All of these outcomes are very likely to be lethal. Finally, flies with balancer chromosomes are easily identified by genetic marker mutations. For example, curly wings or stubbled hair. These phenotypes allow researchers to easily recognize flies that carry

2680-429: The balancer. In the unlikely case of viable recombination, the marker may be lost, thus alerting researchers to the event. Importantly, suppression of recombination by nested inversions only occurs at the inverted intervals, while other regions (usually peri-centromeric and sub-telomeric regions) are free to recombine. Likewise, if the desired mutation is in the same locus as the balancer's recessive lethal mutation (i.e.

2747-429: The benefits of being able to genetically screen populations of organisms for genetic study. Equally as important, they also realized that they could limit crossing over in these populations as well as give them very consistent genetic compositions. The use of balancer chromosomes has since evolved into a well known and widely used method for genetic screening of model organisms. They are even being used to investigate

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2814-476: The chromosome they serve to stabilize and for the phenotypic or genetic marker the balancer carries. The naming of balancer chromosomes in D. melanogaster has been standardized as follows: the first letter of the chromosome's name represents the number of the chromosome it stabilizes. F stands for the first chromosome, S for second, and T for third. The small fourth chromosome does not undergo recombination and therefore does not require balancing. This letter

2881-454: The commonly used TM3, Sb balancer stabilizes the third chromosome and carries a mutant Sb ("stubble") gene as a dominant marker. All flies containing the TM3, Sb balancer will have shortened or stubbly hairs on the back of their abdomens, which are easily seen when viewed through a microscope. The 3 distinguishes this balancer from other third-chromosome balancers such as TM1 and TM2 . A line

2948-411: The correct progeny of each cross can be selected. Stocks double-balanced at both the second and third chromosomes in Drosophila are widely available from fly stock repositories. Balancer chromosomes give geneticists a reliable method for genetically screening organisms for a specific mutation and maintaining that mutation consistently in subsequent generations. A new technique using balancer chromosomes

3015-459: The effect of radiation for SLT, Russell et al. were also interested in studying the effect of chemical mutagens such as procarbazine and ethylnitrosourea for SLT. At that time, procarbazine was the most potent chemical mutagen known to cause a significant spermatogonial mutagenesis in an SLT, although at a rate one-third of that of X-rays. Russell's earlier mutagenesis work on Drosophila using diethylnitrosoamine (DEN) triggered them to use DEN for

3082-406: The fruit fly by Hermann Muller , who pioneered the use of radiation for organismal mutagenesis . In the modern usage of balancer chromosomes, random mutations are first induced by exposing living organisms with otherwise normal chromosomes to substances which cause DNA damage; in flies and nematodes, this usually occurs by feeding larvae ethyl methanesulfonate (EMS). The DNA-damaged larvae (or

3149-436: The function of a gene. In a modifier screen, an organism with a pre-existing phenotype is selected. Thus, any mutations caused by the mutagen (ENU) can be assessed for their enhancive or suppressive activity. Screening for dominant and recessive mutations is performed in a way similar to the conventional genome-wide screen (Figure 7). A number of modifier screens have been performed on Drosophila . Recently, Aliga et al. performed

3216-439: The gene, then this functional copy is capable of complementing the mutated or the lost copy of the gene. In contrast, if both the copies of the gene are mutated or lost, then this will lead to allelic non-complementation (Figure 3) and thus manifestation of the phenotype. The phenomenon of redundancy explains that often multiple genes are able to compensate for the loss of a particular gene. However, if two or more genes involved in

3283-415: The genome, that are associated with the phenotype can be identified. These screens can be designed to identify simple dominant and recessive phenotypes. (Figure 6). Thus an ENU-induced G 0 male is crossed with a wild type female. The G 1 progeny can be screened to identify dominant mutations. However, if the mutation is recessive, then G 3 individuals homozygous for the mutation can be recovered from

3350-501: The lethal recessive in the lines that survived. Figure one in the paper illustrates the screen. This new technique allowed recessive screening in 95% of the Drosophila genome. It also greatly improved yields in germ-line mutations. Another published paper that employed the use of balancer chromosomes is "Inhibition of RNA Interference and Modulation of Transposable Element Expression by Cell Death in Drosophila" . This paper demonstrates

3417-402: The maintenance of recessive lethal (or sterile) mutations within living organisms without interference from natural selection . Since such mutations are viable only in heterozygotes , they cannot be stably maintained through successive generations and therefore continually lead to production of wild-type organisms, which can be prevented by replacing the homologous wild-type chromosome with

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3484-575: The mutation in heterozygous organisms instead (in which a chromosome containing a recessive lethal/sterile mutation is complemented by a homolog that functions as wild-type at the same locus, allowing the organism to survive and reproduce more or less normally). Crosses between heterozygotes yield wild-type organisms in addition to heterozygotes and the non-viable homozygotes. To maintain a purely heterozygous line, wild-type offspring must be identified and prevented from mating. This can be prohibitively resource-intensive, especially if long-term maintenance of

3551-469: The mutation rate was averaged across all 7 loci, ENU was found to induce mutations at a frequency of one per locus in every 700 gametes. Ever since the discovery of ENU as the most potent mutagen by Russell et al. it has been used in forward (phenotype based) genetic screens with which one can identify and study a phenotype of interest. As illustrated in Figure 1, the screening process begins with mutagenising

3618-506: The nematode worm Caenorhabditis elegans and the mouse. Typical balancer chromosomes are designed to (1) carry recessive lethal mutations themselves, eliminating homozygotes which do not carry the desired mutation; (2) suppress meiotic recombination with their homologs, which prevents de novo creation of wild-type chromosomes; and (3) carry dominant genetic markers , which can help identify rare recombinants and are useful for screening purposes. Balancer chromosomes were first used in

3685-431: The older generation of strong Bronsted acids. Complementing alkylation reactions are the reverse, dealkylations. Prevalent are demethylations , which are prevalent in biology, organic synthesis, and other areas, especially for methyl ethers and methyl amines . Balancer chromosome Balancer chromosomes (or simply balancers ) are a type of genetically engineered chromosome used in laboratory biology for

3752-561: The order tertiary amine < secondary amine < primary amine. Typical alkylating agents are alkyl halides. Industry often relies on green chemistry methods involving alkylation of amines with alcohols, the byproduct being water. Hydroamination is another green method for N-alkylation. In the Menshutkin reaction , a tertiary amine is converted into a quaternary ammonium salt by reaction with an alkyl halide . Similar reactions occur when tertiary phosphines are treated with alkyl halides,

3819-485: The power of balancer chromosomes and what can be accomplished with genetically stable lines. A line was established that exhibited low levels of cell death and was named EGFPir hs-hid. When the RNAi levels were analyzed, the authors found interesting results in the cells undergoing low levels of cell death and the surrounding cells in the tissue. They found that these cells would shut down their RNAi mechanism via maintaining RNA in

3886-508: The presence of suitable acid catalysts. For example, most methyl amines are prepared by alkylation of ammonia with methanol. The alkylation of phenols is particularly straightforward since it is subject to fewer competing reactions. More complex alkylation of a alcohols and phenols involve ethoxylation . Ethylene oxide is the alkylating group in this reaction. In the process called oxidative addition , low-valent metals often react with alkylating agents to give metal alkyls. This reaction

3953-450: The presence of the recessive lethal allele on both chromosomal homologs causes the organism to die early in development; an organism that is homozygous for a recessive mutation that causes sterility yields essentially the same result (i.e. its genetic material cannot be passed on to progeny, even if the sterile individual itself survives to maturity). This problem forces geneticists wanting to study recessive lethal/sterile mutations to maintain

4020-527: The products being phosphonium salts. Thiols are readily alkylated to give thioethers via the thiol-ene reaction . The reaction is typically conducted in the presence of a base or using the conjugate base of the thiol. Thioethers undergo alkylation to give sulfonium ions . Alcohols alkylate to give ethers : When the alkylating agent is an alkyl halide, the conversion is called the Williamson ether synthesis . Alcohols are also good alkylating agents in

4087-455: The progression of a disease. Mutation in just one of these genes however, might not contribute significantly to any phenotype. Such "predisposing genes" can be identified using sensitized screens. In this type of a screen, the genetic or environmental background is modified so as to sensitize the mouse to these changes. The idea is that the predisposing genes can be unraveled on a modified genetic or environmental background. Rinchik et al. performed

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4154-437: The recessive mutation is the goal. Substituting a balancer chromosome for the wild-type homolog of the chromosome carrying the recessive mutation prevents the establishment of wild-type organisms in various ways. First, a balancer carries its own independent recessive lethal mutation, which makes the organism non-viable if two copies of balancer are inherited (i.e. no copy of the desired mutation). However, recombination between

4221-399: The researchers' interests. Depending on the region being assessed, forward genetic screens can be classified as illustrated in Figure 2 as: Region specific can be classified as follows: Complementation is the phenomenon which enables generation of the wild type phenotype when organisms carrying recessive mutations in different genes are crossed. Thus if an organism has one functional copy of

4288-424: The role of heterochromatin packing and the effect it has on genes, as well as studies of the effects that telomeres have on gene silencing . In diploid organisms, mutations without recessive lethal (or sterile) phenotypes can simply be bred to homozygosity and maintained stably and indefinitely by crossing homozygotes. However, homozygotes for recessive lethal mutations are by definition non-viable, because

4355-399: The same biological processes or pathways are lost, then this leads to non-allelic non-complementation. In a non-complementation screen, an ENU-induced male is crossed with a female carrying a mutant allele ( a ) of the gene of interest (A). If the mutation is dominant, then it will be present in every generation. However, if the mutation is recessive or if the G 1 progeny are non-viable, then

4422-558: Was also 15 times higher to that obtained with procarbazine (600 mg/kg). To overcome the problem of initial period of sterility, the Russell group showed that instead of injecting one large dose of ENU, a fractionated dose (100 mg/kg) on a weekly schedule permitted a total higher dose (300–400 mg/kg) to be tolerated. This further showed that the mutation frequency improved to be 12 times that of X-rays, 36 times that of procarbazine and over 200 times that of spontaneous mutations. When

4489-443: Was suggested to be used by Ekkehart Vegel to Russell et al. The ENU (250 mg/kg) induced mice underwent a period of sterility for 10 weeks. After recovery, 90 males were crossed to the T -stock females and 7584 pups were obtained. Their results showed that a dose of 250 mg/kg of ENU was capable of producing a mutation rate 5 times higher than that obtained with 600R (1R = 2.6 x10^-4 coulombs/kg) of acute X-irradiation. This rate

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