who discovered that dna can be transferred from one bacterium to another

Transformation in bacteria was first demonstrated in 1928 by British bacteriologist Frederick Griffith.[3] Griffith discovered that a strain of Streptococcus pneumoniae could be made virulent after being exposed to heat-killed virulent strains. Griffith hypothesized that some "transforming principle" from the heat-killed strain was responsible for making the harmless strain virulent. In 1944 this "transforming principle" was identified as being genetic by Oswald Avery, Colin MacLeod, and Maclyn McCarty. They isolated DNA from a virulent strain of S. pneumoniae and using just this DNA were able to make a harmless strain virulent. They called this uptake and incorporation of DNA by bacteria "transformation" (See Avery-MacLeod-McCarty experiment). The results of Avery et al.'s experiments were at first skeptically received by the scientific community and it was not until the development of genetic markers and the discovery of other methods of genetic transfer (conjugation in 1947 and transduction in 1953) by Joshua Lederberg that Avery's experiments were accepted.[4]

Transformation (genetics)

In molecular biology, transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material from its surroundings through the cell membrane(s). For transformation to take place, the recipient bacteria must be in a state of competence, which might occur in nature as a time-limited response to environmental conditions such as starvation and cell density, and may also be induced in a laboratory.[1]

Transformation is one of three processes for horizontal gene transfer, in which exogenous genetic material passes from bacterium to another, the other two being conjugation (transfer of genetic material between two bacterial cells in direct contact) and transduction (injection of foreign DNA by a bacteriophage virus into the host bacterium).[1] In transformation, the genetic material passes through the intervening medium, and uptake is completely dependent on the recipient bacterium.[1]

As of 2014 about 80 species of bacteria were known to be capable of transformation, about evenly divided between Gram-positive and Gram-negative bacteria; the number might be an overestimate since several of the reports are supported by single papers.[1]

"Transformation" may also be used to describe the insertion of new genetic material into nonbacterial cells, including animal and plant cells; however, because "transformation" has a special meaning in relation to animal cells, indicating progression to a cancerous state, the process is usually called "transfection".[2]

It was originally thought that Escherichia coli, a commonly used laboratory organism, was refractory to transformation. However, in 1970, Morton Mandel and Akiko Higa showed that E. coli may be induced to take up DNA from bacteriophage Î» without the use of helper phage after treatment with calcium chloride solution.[5] Two years later in 1972, Stanley Norman Cohen, Annie Chang and Leslie Hsu showed that CaCl
2 treatment is also effective for transformation of plasmid DNA.[6] The method of transformation by Mandel and Higa was later improved upon by Douglas Hanahan.[7] The discovery of artificially induced competence in E. coli created an efficient and convenient procedure for transforming bacteria which allows for simpler molecular cloning methods in biotechnology and research, and it is now a routinely used laboratory procedure.

Transformation using electroporation was developed in the late 1980s, increasing the efficiency of in-vitro transformation and increasing the number of bacterial strains that could be transformed.[8] Transformation of animal and plant cells was also investigated with the first transgenic mouse being created by injecting a gene for a rat growth hormone into a mouse embryo in 1982.[9] In 1907 a bacterium that caused plant tumors, Agrobacterium tumefaciens, was discovered and in the early 1970s the tumor-inducing agent was found to be a DNA plasmid called the Ti plasmid.[10] By removing the genes in the plasmid that caused the tumor and adding in novel genes, researchers were able to infect plants with A. tumefaciens and let the bacteria insert their chosen DNA into the genomes of the plants.[11] Not all plant cells are susceptible to infection by A. tumefaciens, so other methods were developed, including electroporation and micro-injection.[12] Particle bombardment was made possible with the invention of the Biolistic Particle Delivery System (gene gun) by John Sanford in the 1980s.[13][14][15]

Transformation is one of three forms of horizontal gene transfer that occur in nature among bacteria, in which DNA encoding for a trait passes from one bacterium to another and is integrated into the recipient genome by homologous recombination; the other two are transduction, carried out by means of a bacteriophage, and conjugation, in which a gene is passed through direct contact between bacteria.[1] In transformation, the genetic material passes through the intervening medium, and uptake is completely dependent on the recipient bacterium.[1]

Competence refers to a temporary state of being able to take up exogenous DNA from the environment; it may be induced in a laboratory.[1]

It appears to be an ancient process inherited from a common prokaryotic ancestor that is a beneficial adaptation for promoting recombinational repair of DNA damage, especially damage acquired under stressful conditions. Natural genetic transformation appears to be an adaptation for repair of DNA damage that also generates genetic diversity.[1][16]

Transformation has been studied in medically important Gram-negative bacteria species such as Helicobacter pylori, Legionella pneumophila, Neisseria meningitidis, Neisseria gonorrhoeae, Haemophilus influenzae and Vibrio cholerae.[17] It has also been studied in Gram-negative species found in soil such as Pseudomonas stutzeri, Acinetobacter baylyi, and Gram-negative plant pathogens such as Ralstonia solanacearum and Xylella fastidiosa.[17] Transformation among Gram-positive bacteria has been studied in medically important species such as Streptococcus pneumoniae, Streptococcus mutans, Staphylococcus aureus and Streptococcus sanguinis and in Gram-positive soil bacterium Bacillus subtilis.[16] It has also been reported in at least 30 species of Proteobacteria distributed in the classes alpha, beta, gamma and epsilon.[18] The best studied Proteobacteria with respect to transformation are the medically important human pathogens Neisseria gonorrhoeae (class beta), Haemophilus influenzae (class gamma) and Helicobacter pylori (class epsilon)[16]

Naturally competent bacteria carry sets of genes that provide the protein machinery to bring DNA across the cell membrane(s). The transport of the exogenous DNA into the cells may require proteins that are involved in the assembly of type IV pili and type II secretion system, as well as DNA translocase complex at the cytoplasmic membrane.[19]

Due to the differences in structure of the cell envelope between Gram-positive and Gram-negative bacteria, there are some differences in the mechanisms of DNA uptake in these cells, however most of them share common features that involve related proteins. The DNA first binds to the surface of the competent cells on a DNA receptor, and passes through the cytoplasmic membrane via DNA translocase.[20] Only single-stranded DNA may pass through, the other strand being degraded by nucleases in the process. The translocated single-stranded DNA may then be integrated into the bacterial chromosomes by a RecA-dependent process. In Gram-negative cells, due to the presence of an extra membrane, the DNA requires the presence of a channel formed by secretins on the outer membrane. Pilin may be required for competence, but its role is uncertain.[21] The uptake of DNA is generally non-sequence specific, although in some species the presence of specific DNA uptake sequences may facilitate efficient DNA uptake.[22]

Natural transformation is a bacterial adaptation for DNA transfer that depends on the expression of numerous bacterial genes whose products appear to be responsible for this process.[19][23] In general, transformation is a complex, energy-requiring developmental process. In order for a bacterium to bind, take up and recombine exogenous DNA into its chromosome, it must become competent, that is, enter a special physiological state. Competence development in Bacillus subtilis requires expression of about 40 genes.[24] The DNA integrated into the host chromosome is usually (but with rare exceptions) derived from another bacterium of the same species, and is thus homologous to the resident chromosome.

In B. subtilis the length of the transferred DNA is greater than 1271 kb (more than 1 million bases).[25] The length transferred is likely double stranded DNA and is often more than a third of the total chromosome length of 4215 kb.[26] It appears that about 7-9% of the recipient cells take up an entire chromosome.[27]

The capacity for natural transformation appears to occur in a number of prokaryotes, and thus far 67 prokaryotic species (in seven different phyla) are known to undergo this process.[23]

Competence for transformation is typically induced by high cell density and/or nutritional limitation, conditions associated with the stationary phase of bacterial growth. Transformation in Haemophilus influenzae occurs most efficiently at the end of exponential growth as bacterial growth approaches stationary phase.[28] Transformation in Streptococcus mutans, as well as in many other streptococci, occurs at high cell density and is associated with biofilm formation.[29] Competence in B. subtilis is induced toward the end of logarithmic growth, especially under conditions of amino acid limitation.[30]

By releasing intact host and plasmid DNA, certain bacteriophages are thought to contribute to transformation.[31]

Competence is specifically induced by DNA damaging conditions. For instance, transformation is induced in Streptococcus pneumoniae by the DNA damaging agents mitomycin C (a DNA crosslinking agent) and fluoroquinolone (a topoisomerase inhibitor that causes double-strand breaks).[32] In B. subtilis, transformation is increased by UV light, a DNA damaging agent.[33] In Helicobacter pylori, ciprofloxacin, which interacts with DNA gyrase and introduces double-strand breaks, induces expression of competence genes, thus enhancing the frequency of transformation[34] Using Legionella pneumophila, Charpentier et al.[35] tested 64 toxic molecules to determine which of these induce competence. Of these only six, all DNA damaging agents, caused strong induction. These DNA damaging agents were mitomycin C (which causes DNA inter-strand crosslinks), norfloxacin, ofloxacin and nalidixic acid (inhibitors of DNA gyrase that cause double-strand breaks[36]), bicyclomycin (causes single- and double-strand breaks[37]), and hydroxyurea (induces DNA base oxidation[38]). UV light also induced competence in L. pneumophila. Charpentier et al.[35] suggested that competence for transformation probably evolved as a DNA damage response.

Logarithmically growing bacteria differ from stationary phase bacteria with respect to the number of genome copies present in the cell, and this has implications for the capability to carry out an important DNA repair process. During logarithmic growth, two or more copies of any particular region of the chromosome may be present in a bacterial cell, as cell division is not precisely matched with chromosome replication. The process of homologous recombinational repair (HRR) is a key DNA repair process that is especially effective for repairing double-strand damages, such as double-strand breaks. This process depends on a second homologous chromosome in addition to the damaged chromosome. During logarithmic growth, a DNA damage in one chromosome may be repaired by HRR using sequence information from the other homologous chromosome. Once cells approach stationary phase, however, they typically have just one copy of the chromosome, and HRR requires input of homologous template from outside the cell by transformation.[39]

To test whether the adaptive function of transformation is repair of DNA damages, a series of experiments were carried out using B. subtilis irradiated by UV light as the damaging agent (reviewed by Michod et al.[40] and Bernstein et al.[39]) The results of these experiments indicated that transforming DNA acts to repair potentially lethal DNA damages introduced by UV light in the recipient DNA. The particular process responsible for repair was likely HRR. Transformation in bacteria can be viewed as a primitive sexual process, since it involves interaction of homologous DNA from two individuals to form recombinant DNA that is passed on to succeeding generations. Bacterial transformation in prokaryotes may have been the ancestral process that gave rise to meiotic sexual reproduction in eukaryotes (see Evolution of sexual reproduction; Meiosis.)

Artificial competence can be induced in laboratory procedures that involve making the cell passively permeable to DNA by exposing it to conditions that do not normally occur in nature.[41] Typically the cells are incubated in a solution containing divalent cations (often calcium chloride) under cold conditions, before being exposed to a heat pulse (heat shock). Calcium chloride partially disrupts the cell membrane, which allows the recombinant DNA enter the host cell. Cells that are able to take up the DNA are called competent cells.

It has been found that growth of Gram-negative bacteria in 20 mM Mg reduces the number of protein-to-lipopolysaccharide bonds by increasing the ratio of ionic to covalent bonds, which increases membrane fluidity, facilitating transformation.[42] The role of lipopolysaccharides here are verified from the observation that shorter O-side chains are more effectively transformed â€“ perhaps because of improved DNA accessibility.

The surface of bacteria such as E. coli is negatively charged due to phospholipids and lipopolysaccharides on its cell surface, and the DNA is also negatively charged. One function of the divalent cation therefore would be to shield the charges by coordinating the phosphate groups and other negative charges, thereby allowing a DNA molecule to adhere to the cell surface.

DNA entry into E. coli cells is through channels known as zones of adhesion or Bayer's junction, with a typical cell carrying as many as 400 such zones. Their role was established when cobalamine (which also uses these channels) was found to competitively inhibit DNA uptake. Another type of channel implicated in DNA uptake consists of poly (HB):poly P:Ca. In this poly (HB) is envisioned to wrap around DNA (itself a polyphosphate), and is carried in a shield formed by Ca ions.[42]

It is suggested that exposing the cells to divalent cations in cold condition may also change or weaken the cell surface structure, making it more permeable to DNA. The heat-pulse is thought to create a thermal imbalance across the cell membrane, which forces the DNA to enter the cells through either cell pores or the damaged cell wall.

Electroporation is another method of promoting competence. In this method the cells are briefly shocked with an electric field of 10-20 kV/cm, which is thought to create holes in the cell membrane through which the plasmid DNA may enter. After the electric shock, the holes are rapidly closed by the cell's membrane-repair mechanisms.

Most species of yeast, including Saccharomyces cerevisiae, may be transformed by exogenous DNA in the environment. Several methods have been developed to facilitate this transformation at high frequency in the lab.[43]

Efficiency – Different yeast genera and species take up foreign DNA with different efficiencies.[51] Also, most transformation protocols have been developed for baker's yeast, S. cerevisiae, and thus may not be optimal for other species. Even within one species, different strains have different transformation efficiencies, sometimes different by three orders of magnitude. For instance, when S. cerevisiae strains were transformed with 10 ug of plasmid YEp13, the strain DKD-5D-H yielded between 550 and 3115 colonies while strain OS1 yielded fewer than five colonies.[52]

A number of methods are available to transfer DNA into plant cells. Some vector-mediated methods are:

Some vector-less methods include:

Introduction of DNA into animal cells is usually called transfection, and is discussed in the corresponding article.

The discovery of artificially induced competence in bacteria allow bacteria such as Escherichia coli to be used as a convenient host for the manipulation of DNA as well as expressing proteins. Typically plasmids are used for transformation in E. coli. In order to be stably maintained in the cell, a plasmid DNA molecule must contain an origin of replication, which allows it to be replicated in the cell independently of the replication of the cell's own chromosome.

The efficiency with which a competent culture can take up exogenous DNA and express its genes is known as transformation efficiency and is measured in colony forming unit (cfu) per μg DNA used. A transformation efficiency of 1×108 cfu/μg for a small plasmid like pUC19 is roughly equivalent to 1 in 2000 molecules of the plasmid used being transformed.

In calcium chloride transformation, the cells are prepared by chilling cells in the presence of Ca2+ (in CaCl
2 solution), making the cell become permeable to plasmid DNA. The cells are incubated on ice with the DNA, and then briefly heat-shocked (e.g., at 42 °C for 30–120 seconds). This method works very well for circular plasmid DNA. Non-commercial preparations should normally give 106 to 107 transformants per microgram of plasmid; a poor preparation will be about 104/μg or less, but a good preparation of competent cells can give up to ~108 colonies per microgram of plasmid.[54] Protocols, however, exist for making supercompetent cells that may yield a transformation efficiency of over 109.[55] The chemical method, however, usually does not work well for linear DNA, such as fragments of chromosomal DNA, probably because the cell's native exonuclease enzymes rapidly degrade linear DNA. In contrast, cells that are naturally competent are usually transformed more efficiently with linear DNA than with plasmid DNA.

The transformation efficiency using the CaCl
2 method decreases with plasmid size, and electroporation therefore may be a more effective method for the uptake of large plasmid DNA.[56] Cells used in electroporation should be prepared first by washing in cold double-distilled water to remove charged particles that may create sparks during the electroporation process.

Because transformation usually produces a mixture of relatively few transformed cells and an abundance of non-transformed cells, a method is necessary to select for the cells that have acquired the plasmid.[57] The plasmid therefore requires a selectable marker such that those cells without the plasmid may be killed or have their growth arrested. Antibiotic resistance is the most commonly used marker for prokaryotes. The transforming plasmid contains a gene that confers resistance to an antibiotic that the bacteria are otherwise sensitive to. The mixture of treated cells is cultured on media that contain the antibiotic so that only transformed cells are able to grow. Another method of selection is the use of certain auxotrophic markers that can compensate for an inability to metabolise certain amino acids, nucleotides, or sugars. This method requires the use of suitably mutated strains that are deficient in the synthesis or utility of a particular biomolecule, and the transformed cells are cultured in a medium that allows only cells containing the plasmid to grow.

In a cloning experiment, a gene may be inserted into a plasmid used for transformation. However, in such experiment, not all the plasmids may contain a successfully inserted gene. Additional techniques may therefore be employed further to screen for transformed cells that contain plasmid with the insert. Reporter genes can be used as markers, such as the lacZ gene which codes for β-galactosidase used in blue-white screening. This method of screening relies on the principle of α-complementation, where a fragment of the lacZ gene (lacZα) in the plasmid can complement another mutant lacZ gene (lacZΔM15) in the cell. Both genes by themselves produce non-functional peptides, however, when expressed together, as when a plasmid containing lacZ-α is transformed into a lacZΔM15 cells, they form a functional β-galactosidase. The presence of an active β-galactosidase may be detected when cells are grown in plates containing X-gal, forming characteristic blue colonies. However, the multiple cloning site, where a gene of interest may be ligated into the plasmid vector, is located within the lacZα gene. Successful ligation therefore disrupts the lacZα gene, and no functional β-galactosidase can form, resulting in white colonies. Cells containing successfully ligated insert can then be easily identified by its white coloration from the unsuccessful blue ones.

Other commonly used reporter genes are green fluorescent protein (GFP), which produces cells that glow green under blue light, and the enzyme luciferase, which catalyzes a reaction with luciferin to emit light. The recombinant DNA may also be detected using other methods such as nucleic acid hybridization with radioactive RNA probe, while cells that expressed the desired protein from the plasmid may also be detected using immunological methods.


where did the movie couples retreat take place

The primary location for filming was at the St. Regis Bora Bora Resort, Bora Bora in French Polynesia.[4][citation needed] Other filming locations include Los Angeles, Universal Studios and O'Hare International Airport.

Couples Retreat

Couples Retreat is a 2009 American romantic comedy film directed by Peter Billingsley marking his directorial debut, and written by Jon Favreau, Vince Vaughn, Dana Fox, Curtis Hanson, and Greg Beeman. Vaughn and Favreau star with Jason Bateman, Faizon Love, Kristin Davis, Malin Åkerman, Kristen Bell, and Jean Reno. It was released on October 9, 2009, in the United States. The film was shot mostly on the French Polynesian island of Bora Bora. This film has been rated PG-13.

Dave, a dealer for Guitar Hero, and Ronnie, a stay-at-home mom, are a typical couple raising two young children in the suburbs of Chicago. They experience various stresses including redecorating their house and raising their kids. Joey and Lucy are high school sweethearts with a smart but naive teenage daughter named Lacey. Their relationship is on the rocks and they are even considering a divorce once Lacey goes off to college. Jason and Cynthia are a neurotic couple who've experienced multiple failed attempts to conceive, and Shane, who has recently separated from his wife, has a much younger twenty-year-old girlfriend, Trudy.

At Dave's son's birthday party, Jason and Cynthia, using a PowerPoint presentation, announce their troubled marriage and they are considering divorce because they cannot have a baby. As a last-ditch effort, they have found a couples therapy resort named Eden. A deal called the Pelican Package is half the normal cost if they can get three other couples to join them. In their presentation, they show beautiful pictures of sunlit beaches and beautiful locations. They also assure the others that the couples therapy is purely optional.

Dave and Ronnie discuss their inability to go because of childcare responsibilities and decline the trip. In the middle of the night, their home security alarm is activated when Jason shows up unexpectedly to further sell the idea of the retreat. The commotion wakes the kids, who have overheard their parents' conversations of not being able to go because of them. Fearing that their parents are contemplating divorce, the kids have already arranged for Dave's father, Grandpa Jim-Jim to babysit so their parents can go to Eden.

The retreat proves to be divided into Eden West and Eden East. West is for couples and uses the tagline "Stay Together". East is for singles and uses the tagline "Come Together". East and West attendees are not allowed to intermingle.

Upon arrival at Eden West, the four couples are shown their villas. At dinner, resort host Sctanley informs them that couples therapy, which starts at 6 a.m., is actually mandatory. If any couple fails to attend, it will be taken as an indication that they want to leave, and a refund for Eden will be given, although not for their airfare. The group debates what to do. After an indulgent dinner with many delicacies, they decide to put up with "a couple of hours" of therapy in order to enjoy the other amenities of the resort.

In the morning, each couple meets with an assigned therapist. All four couples learn that they have problems, even Ronnie and Dave, who thought they were fine. They endure resort owner Marcel's unusual methods, including swimming with and feeding lemon sharks and yoga sessions with amorous instructor Salvadore.

On the fourth night, Trudy escapes to Eden East. The other seven, encouraged by Joey who is unsatisfied with his marriage, leave to find her. Following an argument between Cynthia and Jason, the men and women split up. As they try to find their way to the resort, the men end up arguing and pointing out each others' marriage mistakes.

The women run into Salvadore who takes them to Eden East. The men come across the staff lounge where they find Sctanley playing Guitar Hero. He threatens to report them to Marcel, but Dave challenges him to the game (without telling Sctanley that he is involved in the game's production). Sctanley, after having lost the wager, directs them to Eden East, even though he knows he was tricked by Dave.

When they arrive, Dave realizes what a good thing he has with Ronnie. He goes with her to be alone at a waterfall. Joey finds Lucy with Salvadore and knocks him out, reuniting with his wife. Cynthia and Jason share drinks and end up becoming intimate. Shane runs into his ex-wife, who admits she still loves him. Shane tells Trudy to remain in Eden East and enjoy being single, then leaves with his ex-wife. All four couples return to Eden West.

Marcel, seeing that the couples have worked out their problems, frees them from the therapy and allows them to go jet skiing, and with that, really enjoy the rest of their vacation.

Vince Vaughn's real-life father, Vernon Vaughn, plays his on-screen father.

Universal Pictures was criticized for removing actors Faizon Love and Kali Hawk from the international posters for the film, showing only six rather than the eight cast members used for the U.S. promotional materials. The studio said it regretted causing offense and has abandoned plans to use the revised poster in other countries.[5][6]

Universal Pictures partnered with various groups for financial support to help market the film. Sponsors include the Tourism Board of Tahiti where the film was made, the manufacturers of Bud Light and Captain Morgan's Rum, Bloomingdale's department store, and Crunch Gyms. The video game Guitar Hero is also prominently featured in the film as it is considered one of the best games ever made.

Couples Retreat received generally negative reviews from critics. On Rotten Tomatoes the film has an approval rating of 11% based on 159 reviews with an average rating of 3.6/10. The site's critical consensus reads, "Despite a talented cast and some reliably pleasant interplay between Jon Favreau and Vince Vaughn, Couples Retreat leaves viewers stranded in an arid, mirthless comedy."[7] On Metacritic, the film has a score of 23 out of 100 based on 27 critics, indicating "generally unfavorable reviews".[8] Audiences polled by CinemaScore gave the film an average grade of "B" on an A+ to F scale.[9]

A former model and current salon stylist, Irina Krupnik, filed a $10 million misappropriation-of-likeness invasion-of-privacy lawsuit, naming several defendants including the producers of Couples Retreat arising from a purported masturbation scene in which actor Jon Favreau uses a photo of her.[10] Manhattan Supreme Court Judge O. Peter Sherwood ruled against Krupnik, and she received nothing.[11]

Despite the negative critical reception, it was a box office success, ranking first for its opening weekend grossing $34,286,740 and becoming Vince Vaughn's highest box office success since 2006's The Break-Up. The film has grossed $109.2 million domestically and $58.8 million in foreign markets for a worldwide total of $171 million.[3]


what is the role of the llc sublayer

In the IEEE 802 reference model of computer networking, the logical link control (LLC) data communication protocol layer is the upper sublayer of the data link layer (layer 2) of the seven-layer OSI model. The LLC sublayer provides multiplexing mechanisms that make it possible for several network protocols (e.g. IP, IPX, Decnet and Appletalk) to coexist within a multipoint network and to be transported over the same network medium. It can also provide flow control and automatic repeat request (ARQ) error management mechanisms.

Logical link control

The LLC sublayer acts as an interface between the media access control (MAC) sublayer and the network layer.

The LLC sublayer is primarily concerned with multiplexing protocols transmitted over the MAC layer (when transmitting) and demultiplexing them (when receiving).
It can also provide node-to-node flow control and error management.

The flow control and error management capabilities of the LLC sublayer are used by protocols such as the NetBIOS Frames protocol. However, most protocol stacks running atop 802.2 do not use LLC sublayer flow control and error management. In these cases flow control and error management are taken care of by a transport layer protocol such as TCP or by some application layer protocol. These higher layer protocols work in an end-to-end fashion, i.e. re-transmission is done from the original source to the final destination, rather than on individual physical segments. For these protocol stacks only the multiplexing capabilities of the LLC sublayer are used.

An LLC sublayer was a key component in early packet switching networks such as X.25 networks with the LAPB data link layer protocol, where flow control and error management were carried out in a node-to-node fashion, meaning that if an error was detected in a frame, the frame was retransmitted from one switch to next instead. This extensive handshaking between the nodes made the networks slow.

The IEEE 802.2 standard specifies the LLC sublayer for all IEEE 802 local area networks, such as IEEE 802.3/Ethernet (if the EtherType field is not used), IEEE 802.5, and IEEE 802.11.  IEEE 802.2 is also used in some non-IEEE 802 networks such as FDDI.

Since bit errors are very rare in wired networks, Ethernet does not provide flow control or automatic repeat request (ARQ), meaning that incorrect packets are detected but only cancelled, not retransmitted (except in case of collisions detected by the CSMA/CD MAC layer protocol). Instead, retransmissions rely on higher layer protocols.

As the EtherType in an Ethernet frame using Ethernet II framing is used to multiplex different protocols on top of the Ethernet MAC header it can be seen as an LLC identifier. However, Ethernet frames lacking an EtherType have no LLC identifier in the Ethernet header, and, instead, use an IEEE 802.2 LLC header after the Ethernet header to provide the protocol multiplexing function.

In wireless communications, bit errors are very common. In wireless networks such as IEEE 802.11, flow control and error management is part of the CSMA/CA MAC protocol, and not part of the LLC layer. The LLC sublayer follows the IEEE 802.2 standard.

Some non-IEEE 802 protocols can be thought of as being split into MAC and LLC layers.  For example, while HDLC specifies both MAC functions (framing of packets) and LLC functions (protocol multiplexing, flow control, detection, and error control through a retransmission of dropped packets when indicated), some protocols such as Cisco HDLC can use HDLC-like packet framing and their own LLC protocol.

Over telephone network modems, PPP link layer protocols can be considered as a LLC protocol, providing multiplexing, but it does not provide flow control and error management. In a telephone network, bit errors might be common, meaning that error management is crucial, but that is today provided by modern protocols. Today's modem protocols have inherited LLC features from the older LAPM link layer protocol, made for modem communication in old X.25 networks.

The GPRS LLC layer also does ciphering and deciphering of SN-PDU (SNDCP) packets.

Another example of a data link layer which is split between LLC (for flow and error control) and MAC (for multiple access) is the ITU-T G.hn standard, which provides high-speed local area networking over existing home wiring (power lines, phone lines and coaxial cables).


where is daisy from in the great gatsby

Daisy Fay was born into a wealthy Louisville family. By 1917, Daisy had several suitors of her same class, but fell in love with Jay Gatsby, a poor soldier. Before Gatsby left for war, Daisy promised to wait for him. After Gatsby started attending Trinity College, Oxford, Daisy sent him a letter revealing that she had married Tom Buchanan. During the marriage, Daisy gave birth to a daughter, Pammy, who Daisy had hoped would be "a beautiful little fool." Daisy and her family settled in East Egg, a wealthy old money  enclave in Long Island.

Daisy Buchanan

Daisy Fay Buchanan is a fictional character in F. Scott Fitzgerald's magnum opus The Great Gatsby (1925). In the novel, Daisy is depicted as a married woman with a daughter who is reunited with her former lover Jay Gatsby, arousing the jealousy of her husband, Tom. She is widely believed to have been based on Ginevra King.[1] She has appeared in various media related to the novel including feature films and plays.

After her cousin Nick Carraway arrives in West Egg, the neighboring island, he meets Gatsby, who by now has become extremely wealthy. Gatsby throws several large, extravagant parties in hopes that Daisy will attend.[2] Nick successfully sets up a meeting between Daisy and Jay at his neighboring cottage in West Egg where the two meet for the first time in five years, which leads to an affair.[3]

At the Buchanan home, Daisy, Tom, Gatsby, Nick and his girlfriend Jordan Baker decide to visit New York City, Tom taking Gatsby's yellow Rolls Royce with Jordan and Nick while Daisy and Gatsby drive alone. Once the group reach the city, they throw a party that turns into a confrontation between Daisy, Tom and Gatsby. Though Gatsby insisted that Daisy never loved Tom, Daisy admits that she loves both Tom and Gatsby. The party ends with Daisy driving Gatsby out of New York City in Tom's car, while Tom leaves with Nick and Jordan. Tom's mistress Myrtle Wilson, who earlier had a falling out with Tom, runs in front of Tom's car in hopes of reconciling with Tom. Daisy does not see her until it is too late, and runs her over. Daisy, panicked, drives away from the scene of the accident. In her home in East Egg, Gatsby assures her that he will take the blame. Tom tells George, Myrtle's husband, that it was Gatsby's car that killed Myrtle. George goes to Gatsby's home in West Egg and shoots Gatsby dead before turning the gun on himself. After Gatsby's murder, Daisy, Tom, and their daughter leave East Egg, having no forwarding address.

The first adaptation of The Great Gatsby was a silent film produced in 1926 and featured Lois Wilson as Daisy.  The film is now considered lost.

In 1949, another film was made, starring Alan Ladd as Gatsby and Betty Field as Daisy.

Phyllis Kirk portrayed Daisy in a 1955 episode of the television series Robert Montgomery Presents adapting The Great Gatsby.

Jeanne Crain played Daisy in a 1958 episode of the television series Playhouse 90.

In the 1974 film adaptation, Daisy is portrayed by Mia Farrow. A photo of Farrow portraying Daisy appeared on the cover of the first issue of People magazine in promotion of the then-upcoming film. In the photo, Farrow holds a string of pearls in her hand while the pearls are also in her mouth.[4] It was later emulated in 2014 by Taylor Swift.[5] Farrow's performance as Daisy was met with mixed reception, Bruce Handy of Vanity Fair praising Farrow as being "full of vain flutter and the seductive instant intimacy of the careless rich"[6] while Leigh Paatsch of News.com.au thought Farrow missed Daisy "by a country mile."[7] While Vincent Canby of The New York Times wrote favorably of Farrow as Daisy, he added that Daisy "may be an impossible role, one that is much more easily accepted on the page than on the screen."[8]

Mira Sorvino played Daisy in the 2000 film adaptation.

In the 2013 film adaptation, Daisy is portrayed by Carey Mulligan.[9] Mulligan had two 90-minute auditions, which she found to be fun and served as her initial encounters with Leonardo DiCaprio, who portrayed Gatsby, and who read with her both days. Mulligan left the audition, unsure she had secured the role, but was satisfied to have played off DiCaprio.[10] Mulligan read the novel in preparation for auditioning for the role, finding the book to be accessible due to its length. Mulligan was familiar with the dislike some readers of The Great Gatsby had for the character, but felt she could not "think that about her, because I can't play her thinking she's awful." Mulligan strayed from watching Farrow's prior portrayal of Daisy, believing she might steal from Farrow's performance subconsciously for her own.[11] Director Baz Luhrmann confirmed Mulligan had been cast as Daisy in November 2010, one month after she acquired the role.[12] After the confirmation, Time assessed Mulligan as being attractive but in a childlike way, a contrast to Daisy's womanly beauty in the novel.[13] Todd McCarthy of The Hollywood Reporter in his review of the film wrote that viewers had their own ideals about Daisy's character and would debate whether Mulligan "has the beauty, the bearing, the dream qualities desired for the part, but she lucidly portrays the desperate tear Daisy feels between her unquestionable love for Gatsby and fear of her husband."[14]

Tricia Paoluccio portrayed Daisy in the American Masters episode "Novel Reflections: The American Dream".  Starting in 2006, in the Simon Levy version of the play, Daisy was portrayed by Heidi Armbruster, who according to Quinton Skinner, "is full of loony momentary enthusiasms and a dangerous sensuality, though by the second act, Armbrusterâ€™s perf veers toward hollow mannerisms."[15] Daisy was portrayed by Monte McGrath in the 2012 version of the play, and her performance was met with acclaim.[16] Daisy is portrayed by Madeleine Herd in an adaptation by Independent Theater productions.[17]

According to his own letters and diary entries, Fitzgerald's character of Daisy was based on Chicago socialite and debutante, Ginevra King.[18][19][1] He had met on a visit back home in St. Paul, Minnesota while enrolled as a student at Princeton University.[20] Immediately infatuated with her, according to his biographer Andrew Mizner, Fitzgerald "remained devoted to Ginevra as long as she would allow him to", wrote to her "daily the incoherent, expressive letters all young lovers write",[21] and she would become his inspiration for Daisy, as well as several other characters in his novels and short stories.[21][22]

The curator of Fitzgerald manuscripts and letters at Princeton, Don Skemer, has written that Ginerva "remained for Fitzgerald an archetype for the alluring, independent and upper class woman, ultimately unattainable by someone of a modest social background like himself", and that she "was a model for Daisy", as well as being "recognizable in many other [Fitzgerald] characters."[23]

There is also evidence of Daisy being partially based on Fitzgerald's wife Zelda.[24] Theresa Anne Fowler has written of the similarities that both Daisy and Zelda shared: "the Southern upbringing, the prominent family. And it is no secret that Scott borrowed liberally from Zelda’s early diaries and their own life for his stories."[24] And, when their daughter Scottie was born, Zelda, upon emerging from the anesthesia, was reported to have expressed her hope that their child would be a "beautiful little fool"—one of Daisy's lines, among many others, that have been attributed to Zelda.[24]

When first introduced, Daisy is shown to speak in a manner that is childlike and without any knowledge of what is correct. She fakes ignorance when speaking in Tom's presence but then reveals her actual feelings to Nick, including the fact that she had hoped her daughter would be unintelligent. From this, it is implied that her mannerisms are not some mere attempt at fooling those around her but actually contribute to an ongoing effort to serve as a role model toward her daughter and be directly responsible for her not learning much and becoming the "beautiful little fool" that she had aspired to have for a child. Daisy's motivations in wanting this are revealed by her to be that of hoping that her daughter is spared the unpleasant events that can occur in one's life and rooted in her view that she will not be affected by the emotional pain of her life as in being moronic, she cannot understand the events transpiring around her.

Though she is faithful to her husband in the years of their marriage leading up to Gatsby's return, she jumps nearly instantly at the chance of being able to have an affair with Gatsby. While it appears at first that this is a mere relationship of lust between two former lovers that are seeking to reignite an old flame, it is later revealed by Daisy's words to Tom after he learns of the relationship that she went along with it due to her feeling of neglect by her husband. Not only did her neglect drive her to the point of breaking a vow, but so did her ambitions to have an actual fulfilling relationship for the first time since shortly after she married, as Daisy reveals the lack of intimacy between her and Tom, further evidenced by his continued decline to show her any type of consideration in their shared appearances. Daisy's reluctance to accept Tom's claims of remorse demonstrate that her trust is not earned easily and the fact that she continues seeing Gatsby following this proves that she was not as concerned with the consequences of her cheating than that of her happiness.

Looking at Daisy’s character, one can see she did care for Gatsby, though maybe not as much as she ended up caring for Tom. Daisy was important to Gatsby because Daisy made Gatsby feel loved. Though no matter what Gatsby did to win Daisy’s affection, she married Tom and remained married to him despite Gatsby’s pursuit of her. “[Gatsby’s] efforts to attain Daisy…are no more successful, as she abandons him and he realizes too late that he has set his sights on the wrong goal.” [25] Daisy is “a woman who gives birth to a child, cheats on her husband, kills another person, and allows Gatsby to take the blame for her mistake.”[26] This says much about Daisy’s character, because Daisy seems to think that she can do what she wants without needing to worry about the consequences of her actions, nor how they affect other people. Beginning when Gatsby left the first time for the army, for she could never seem to find someone to fill the hole that which Gatsby had left: “Wild rumors were circulating about her…After that she didn’t play around with the soldiers any more but only with a few flat-footed, short sighted young men in town who couldn’t get into the army at all.” [27] Then there came the time for Daisy to marry Tom, but she wanted to “change’ her mind!” for she knew that she loved Gatsby still, but decided not to do anything about her conflicted heart.[28]

Daisy has become associated with wealth,[29] victims of marital affairs,[30] and glamor.[31][32] Since the Baz Luhrmann live action film was released, featuring Daisy with a bob cut, certain versions of the hairstyle are attributed to her.[33][34]
Actress Carey Mulligan, who portrayed Daisy in the 2013 film adaptation, said Daisy was similar to members of the Kardashian family, later stating, "what I was trying to imply was that there’s an essence of part of the amazing business they run as the Kardashians is looking beautiful a lot and looking very present, presentational and perfect.”[35] Since the comparisons, members of the Kardashian family have been compared to Daisy.[36] Shaun Fitzpatrick of Bustle compared Daisy with Henrietta Bingham, the lead character in the novel Irresistible: The Jazz Age Life of Henrietta Bingham, even using images of Daisy when talking about actions of the character since as Fitzpatrick wrote, she was similar to "a character in an F. Scott Fitzgerald novel".[37] Inga Ting of The Sydney Morning Herald used an image of Mulligan as Daisy in an article titled, "Men want beauty, women want money: what we want from the opposite sex".[38] The character's physical description has become synonymous with 1920s culture.[39]

Emma Gray of The Huffington Post wrote of Daisy, "As F. Scott Fitzgerald's twisted 1920s version of a manic pixie dream girl, The Great Gatsby antiheroine has become one of the most discussed and polarizing female characters in American literature."[40] An afterward in the 1992 edition of the novel by publisher Charles Scribner III claimed that Fitzgerald blamed the initial commercial failure of The Great Gatsby on it containing "

Daisy has been vilified for the consequences of her actions, such as directly and indirectly causing the deaths of several characters, and has even been considered the true antagonist of the novel. She ranked No. 1 on 10 On Screen Villains that Will Make Your Blood Boil, Part 2 on Moviepilot, a list consisting entirely of female film characters.[46] Bloom wrote that, although Daisy was not technically the villain of the story, "she still sucks, and if it weren’t for her a couple key players in the book would be alive at the end of it." Bloom then dedicated the subsequent list of her top ten detestable literary characters to Daisy.[47] Despite the criticism, some commentators have sympathized with the character. Katie Baker of The Daily Beast concluded that though Daisy lives and Gatsby dies, "in the end both Gatsby and Daisy have lost their youthful dreams, that sense of eternal possibility that made the summertimes sweet. And love her or hate her, there’s something to pity in that irrevocable fact."[41] Dave McGinn listed the character as one who needed their side of the story in their novel told, questioning if she really had a "voice full of money" as Gatsby claimed and wondered what her thoughts were on the love triangle between her, Gatsby and her husband.[48]