Twin

Fraternal twin boys in the tub

The term twin most notably refers to two individuals (or one of two individuals) who have shared the same uterus (womb) and are usually, but not necessarily, born on the same day. A fetus alone in the womb is called a singleton. Due to the limited size of the mother's womb, multiple pregnancy is much less likely to carry to full term than singleton birth (twins usually around 34 to 36 weeks). Since some premature births often have health consequence to the babies, twins birth are often handled with special procedures.

Types of twins

Fraternal twins

Fraternal twins (commonly known as "non-identical twins") usually occur when two fertilized eggs are implanted in the uterine wall at the same time. The two eggs form two zygotes, and these twins are therefore also known as dizygotic as well as "biovular" twins.

Dizygotic twins, like any siblings, have a very small chance of having the exact same chromosome profile, but most likely have a number of different chromosomes that distinguish them. Dizygotic twins may be a different sex or the same sex, just as with any other siblings.

Studies show that there is a genetic basis for fraternal twinning—that is, non-identical twins do run in families. However, it is only the female that has any influence on the chances of having fraternal twins as the male cannot make her release more than one ovum.

Identical twins

Identical twins occur when a single egg is fertilized to form one zygote (monozygotic) but the zygote then divides into two separate embryos. The two embryos develop into fetuses sharing the same womb. Depending on the stage at which the zygote divides, identical twins may share the same amnion (in which case they are known as monoamniotic) or not (diamniotic). Diamniotic identical twins may share the same placenta (known as monochorionic) or not (dichorionic). All monoamniotic twins are monochorionic. Also note that any monochorionic or monoamniotic twins are identical twins. This condition does not occur for fraternal twins.

The later in pregnancy that twinning occurs, the more structures will be shared. Zygotes that twin at the earliest stages will be diamniotic and dichorionic ("di-di"). Twinning between 4 to 8 days after fertilization typically results in monochorionic-diamniotic ("mono-di") twins. Twinning between 8 to 12 days after fertilization will usually result in monochorionic-monoamniotic ("mono-mono") twins. Twinning after 12 days post-fertilization will typically result in conjoined twins.

Sharing the same amnion (or the same amnion and placenta) can cause complications in pregnancy. For example, the umbilical cords of monoamniotic twins can become entangled, reducing or interrupting the blood supply to the developing fetus. Monochorionic twins, sharing one placenta, usually also share the placental blood supply. These twins may develop such that blood passes disproportionately from one twin to the other through connecting blood vessels within their shared placenta, leading to twin-to-twin transfusion syndrome. About 50% of mono-mono twins die from umbilical cord entanglement.

Monozygotic twins are genetically identical unless there has been a mutation in development, and they are almost always the same gender. (On extremely rare occasions, an original XXY zygote may form monozygotic boy/girl twins by dropping the Y chromosome for one twin and the extra X chromosome for the other.) Monozygotic twins generally look alike, although sometimes they appear as mirror images of each other. Examination of details such as fingerprints can tell them apart. As they mature, identical twins often become less alike because of lifestyle choices or external influences such as scars.

While it was originally thought that identical twins do not run in families, but occur more or less randomly, some recent research has suggested that a genetic predisposition may exist. The exact cause for the splitting of a zygote or embryo is unknown.

Identical twins can behave as differently as any other siblings (a matter of much interest to psychologists). They develop their own individual personalities to enable themselves to be identified as individual persons. Many identical twins spend most of their time together (especially as children), so people often assume that they will behave alike just as they look alike; however, this is not the case. Twins are unique individuals that establish their own individual likes and dislikes. There are usually obvious signs of differences when the identical twins are observed separately or together.

Identical twins have identical DNA but differing environmental influences throughout their lives affect which genes are switched on or off. This is called epigenetic modification. A study of 80 pairs of twins ranging in age from 3 to 74 showed that the youngest twins have relatively few epigenetic differences. The number of differences between identical twins increases with age. 50-year-old twins had over 3 times the epigenetic difference that the 3-year-old twins had. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference. (Fraga, et al., 2005).

Some percentage of monozygotic twins are called "mirror twins" or mirror image twins. These are identical twins with opposite features, that is one may be right handed and the other may be left handed; hair will whorl in the opposite direction, and so on. The incidence of mirror twinning is comparatively rare. They result from a late split of the fertilized egg at around 9-12 days. One mirror may or may not have situs inversus. This is where some or all of the organs will be on the opposite side of the body, such as the heart being on the right(Dextrocardia). Such conditions are usually associated with a higher incidence of other birth defects.

Complications of twin pregnancy

Vanishing twins

Researchers suspect that more pregnancies start out as multiples than come to term that way. Early obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes.

Conjoined twins

Conjoined twins are monozygotic twins, whose bodies are joined together at birth. This occurs where the single zygote of identical twins fails to separate completely. This condition occurs in about 1 in 100,000 pregnancies.

Parasitic twins

Sometimes one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. One fetus acts as a parasite towards the other.

Sometimes the parasitic twin just becomes an almost indistinguishable part of the other.

A chimera is a person who is a completely normal human with no extra parts, but some of the parts actually came from his or her twin. A chimera may arise either from identical twin fetuses (where it would be impossible to detect), or from dizygotic fetuses, which could be identified by chromosomal comparisons from various parts of the body.

Miscarried twin

Occasionally, a woman will suffer a miscarriage early in pregnancy, yet the pregnancy will continue; one twin was miscarried but the other was able to be carried to term. Similar to vanishing twin.

Human twins

Historically, about 1 in 80 human births (1.2%) has been the result of a twin pregnancy. The rate of twinning varies greatly among ethnic groups, ranging as high as about 6% for the Yoruba or 10% for a tiny Brazilian village (see [1]). The widespread use of fertility drugs causing hyperovulation (stimulated release of multiple eggs by the mother) has caused what some call an "epidemic of multiple births". In 2001, for the first time ever in the US, the twinning rate exceeded 3% of all births. Thus, approximately 6% of children born in the US in 2001 were twins.

Nevertheless, the rate of identical twins remains at about 1 in 250 across the globe, further suggesting that pregnancies resulting in identical twins occur randomly.

Multiple births

Sometimes multiple births may involve more than two fetuses. If there are three, they are called triplets; four, quadruplets; five, quintuplets; six, sextuplets, seven, septuplets, and so on. Before the advent of ovulation-stimulating drugs, triplets were quite rare (approximately 1 in 8000 births) and higher order births so rare as to be almost unheard of. Multiple pregnancies are usually delivered before the full term of 40 weeks gestation: the average length of pregnancy is around 36 weeks for twins, 34 weeks for triplets and 32 weeks for quadruplets.

Predisposing factors

The cause of monozygotic twinning is unknown. Fewer than 20 families have been described with an inherited tendency towards monozygotic twinning (people in these families have nearly a 50% chance of delivering monozygotic twins). Some evidence suggests that the environment of the womb causes the zygote to split in most cases.

Dizygotic twin pregnancies are slightly more likely when the following factors are present in the woman:

  • She is of African descent
  • Between the age of 30 and 40 years
  • Greater than average height and weight
  • Several previous pregnancies.

Women undergoing certain fertility treatments may have a greater chance of multiple births. This can vary depending on what types of fertility treatments are used. With in vitro fertilisation (IVF), this is primarily due to the insertion of multiple embryos into the uterus. Some other treatments such as the drug Clomid can stimulate a woman to release multiple eggs, allowing the possibility of multiples. Many fertility treatments have no effect on the likelihood of multiple births.

Twin studies

Twin studies are studies that assess identical (monozygotic) twins for medical, genetic, or psychological characteristics to try to isolate genetic influence from environmental influence. Twins that have been separated early in life and raised in separate households are especially sought-after for these studies, which have been invaluable in the exploration of human nature.

Unusual Twinnings

There are some patterns of twinning that are exceedingly rare: while they have been reported to happen, they are so unusual that most obstetricians or midwives may go their entire careers without encountering a single case.

Among fraternal twins, in rare cases, the eggs are fertilised at different times with two or more acts of sexual intercourse, either within one menstrual cycle (superfecundation) or, even more rarely, later on in the pregnancy (superfetation). This can lead to the possibility of a woman carrying fraternal twins with different fathers (that is, half-siblings). One 1992 study estimates that the frequency of heteropaternal superfecundation among dizygotic twins whose parents were involved in paternity suits was approximately 2.4%; see the references section, below, for more details.

Among monozygotic twins, in extremely rare cases, twins have been born with opposite sexes (one male, one female). The probability of this is so vanishingly small (only 3 documented cases) that multiples having different genders is universally accepted as a sound basis for a clinical determination that in utero multiples are not monozygotic. When monozygotic twins are born with different genders it is because of chromosomal birth defects. In this case, although the twins did come from the same egg, it is incorrect to refer to them as genetically identical, since they have different karyotypes.

Twinning in animals

Multiple births are common in many animal species, such as cats, sheep, and ferrets. The incidence of twinning among cattle is about 1-4%, and research is underway to improve the odds of twinning, which can be more profitable for the breeder if complications can be sidestepped or managed.


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The incidence of twinning among cattle is about 1-4%, and research is underway to improve the odds of twinning, which can be more profitable for the breeder if complications can be sidestepped or managed. Computer and video games are a subset of interactive media, which includes virtual reality, flight and engineering simulation, multimedia and the World Wide Web. Multiple births are common in many animal species, such as cats, sheep, and ferrets. Gamers are quite happy to use the vague term "games", or "videogame/video game" to distinguish them from board games and card games when necessary. In this case, although the twins did come from the same egg, it is incorrect to refer to them as genetically identical, since they have different karyotypes. Other commonly used terms include "entertainment software," "interactive entertainment media," "electronic interactive entertainment," "electronic game," "software game," and "videogame" (as one word). When monozygotic twins are born with different genders it is because of chromosomal birth defects. For many, either "computer game" or "video game" describes these games as a whole.

The probability of this is so vanishingly small (only 3 documented cases) that multiples having different genders is universally accepted as a sound basis for a clinical determination that in utero multiples are not monozygotic. Non-gamers use several umbrella terms for console, PC, arcade, handheld, and similar games since they do not agree on the best name. Among monozygotic twins, in extremely rare cases, twins have been born with opposite sexes (one male, one female). See artistic computer game modification and Machinima. One 1992 study estimates that the frequency of heteropaternal superfecundation among dizygotic twins whose parents were involved in paternity suits was approximately 2.4%; see the references section, below, for more details. Recently, computer games have also been used as a digital art medium. This can lead to the possibility of a woman carrying fraternal twins with different fathers (that is, half-siblings). After the release of Half-Life 2 Valve developed these mods for the sequel and sold them through their Internet digital distribution software, Steam.

Among fraternal twins, in rare cases, the eggs are fertilised at different times with two or more acts of sexual intercourse, either within one menstrual cycle (superfecundation) or, even more rarely, later on in the pregnancy (superfetation). Valve bought a number of popular mods including Counter-Strike and Day of Defeat. There are some patterns of twinning that are exceedingly rare: while they have been reported to happen, they are so unusual that most obstetricians or midwives may go their entire careers without encountering a single case. This was the case with Valve's Half-Life. Twins that have been separated early in life and raised in separate households are especially sought-after for these studies, which have been invaluable in the exploration of human nature. Popular mods are very occasionally bought by the developers of the game. Twin studies are studies that assess identical (monozygotic) twins for medical, genetic, or psychological characteristics to try to isolate genetic influence from environmental influence. Developers such as id, Valve, and Epic ship their games with the very development tools used to make the game in the first place, along with documentation to assist mod developers, which allows for the kind of success seen by popular mods such as Counter-Strike.

Many fertility treatments have no effect on the likelihood of multiple births. The Internet provides an inexpensive medium to promote and distribute mods, and they have become an increasingly important factor in the commercial success of some games. Some other treatments such as the drug Clomid can stimulate a woman to release multiple eggs, allowing the possibility of multiples. These mods can add an extra dimension of replayability and interest. With in vitro fertilisation (IVF), this is primarily due to the insertion of multiple embryos into the uterus. Games running on a PC are often designed with end-user modifications in mind, and this consequently allows modern computer games to be modified by gamers without much difficulty. This can vary depending on what types of fertility treatments are used. See also: video game industry practices.

Women undergoing certain fertility treatments may have a greater chance of multiple births. This has led to regular occurrences of missed deadlines and unfinished products; Duke Nukem Forever is the quintessential example of these problems. Dizygotic twin pregnancies are slightly more likely when the following factors are present in the woman:. The average team size as well as the average development time of a game have grown along with the size of the industry and the technology involved in creating games. Some evidence suggests that the environment of the womb causes the zygote to split in most cases. Most video game console development teams number anywhere from 20 to 50 people, with some teams exceeding 100. Fewer than 20 families have been described with an inherited tendency towards monozygotic twinning (people in these families have nearly a 50% chance of delivering monozygotic twins). Video games are developing fast in all areas, but the problem is of cost, and how developers intend to keep the costs low enough to attract publisher investment.

The cause of monozygotic twinning is unknown. Development by committee rarely works. Multiple pregnancies are usually delivered before the full term of 40 weeks gestation: the average length of pregnancy is around 36 weeks for twins, 34 weeks for triplets and 32 weeks for quadruplets. The visionary for any game may come from any of the roles outlined. Before the advent of ovulation-stimulating drugs, triplets were quite rare (approximately 1 in 8000 births) and higher order births so rare as to be almost unheard of. Now, development commonly requires a large team consisting of designers, graphic designers and other artists, programmers, sound designers, musicians, and other technicians; all of which are managed by producers. If there are three, they are called triplets; four, quadruplets; five, quintuplets; six, sextuplets, seven, septuplets, and so on. Video games are made by developers, who used to do this as individuals or small teams in the 80's.

Sometimes multiple births may involve more than two fetuses. It's only a matter of time before video games will be as accepted as other forms of media and entertainment. Nevertheless, the rate of identical twins remains at about 1 in 250 across the globe, further suggesting that pregnancies resulting in identical twins occur randomly. In both cases, the attempts at censorship in the United States were struck down as a violation of First Amendment rights, and they have gone on to become fully integrated facets of society. Thus, approximately 6% of children born in the US in 2001 were twins. Since these art forms have been around longer, the backlash against them occurred farther in the past, beyond the remembrance of today's youth. In 2001, for the first time ever in the US, the twinning rate exceeded 3% of all births. Moreover, it appears to be a question of age.

The widespread use of fertility drugs causing hyperovulation (stimulated release of multiple eggs by the mother) has caused what some call an "epidemic of multiple births". The same situation has been applied to Comic books, music, and motion pictures. The rate of twinning varies greatly among ethnic groups, ranging as high as about 6% for the Yoruba or 10% for a tiny Brazilian village (see [1]). Historically, this type of controversy and criticism is not unique to video games. Historically, about 1 in 80 human births (1.2%) has been the result of a twin pregnancy. Proponents and opponents of censorship are often very passionate about their individual views. Similar to vanishing twin. Video game controversy comes in many forms, and censorship is a controversial subject, as well as a popular topic of debate.

Occasionally, a woman will suffer a miscarriage early in pregnancy, yet the pregnancy will continue; one twin was miscarried but the other was able to be carried to term. Video game censorship is defined as the use of state or group power to control the playing, distribution, purchase, or sale of video games or computer games. A chimera may arise either from identical twin fetuses (where it would be impossible to detect), or from dizygotic fetuses, which could be identified by chromosomal comparisons from various parts of the body. Among others, critics of video games sometimes include parents' groups, politicians, organized religion groups, and other special interest groups, even though all these can be found in all forms of entertainment and media. A chimera is a person who is a completely normal human with no extra parts, but some of the parts actually came from his or her twin. Computer and video games have been the subject of frequent controversy and censorship, due to the depiction of graphic violence, sexual themes, advertising, consumption of illegal drugs, consumption of alcohol or tobacco, propaganda or profanity in some games. Sometimes the parasitic twin just becomes an almost indistinguishable part of the other. Development of techniques are tested against an advanced computer player or online against other human players.

One fetus acts as a parasite towards the other. A well-designed game will be easy to pick up but difficult to master, like chess. Sometimes one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. Games which encourage strategic thinking have well-honed rule sets that the player needs to thoroughly grasp. This condition occurs in about 1 in 100,000 pregnancies. For example an RTS game set in the past may require use of ancient armies or outwitting a famous world leader of the time. This occurs where the single zygote of identical twins fails to separate completely. More obvious benefits to the player is education on the game's subject matter.

Conjoined twins are monozygotic twins, whose bodies are joined together at birth. It could be said that when players stare at a screen with a blank expression, it isn't one of hopeless mesmerization, but one of intense concentration. Early obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes. To win at a game, the player may devote his/her entire attention to it, and utilise newly-learnt skills or tactics. Researchers suspect that more pregnancies start out as multiples than come to term that way. An experienced player will be able to do all this in a very short period of time upon first discovering a new game- such quick learning skills can easily be transferred to other areas of mental application. Such conditions are usually associated with a higher incidence of other birth defects. S/he must then learn the game controls and how the human-machine interface works, inclusing menus and HUDs.

This is where some or all of the organs will be on the opposite side of the body, such as the heart being on the right(Dextrocardia). In order to experience the game, the player must first determine the objective(s), as well as how to complete them. One mirror may or may not have situs inversus. Computer and videogames differ from other forms of entertainment in that the person experiencing them is in control, one way or another. They result from a late split of the fertilized egg at around 9-12 days. Online shows are fast becoming the place to view live action gaming broadcasts such as Gamespot's 'On the Spot'. The incidence of mirror twinning is comparatively rare. Other parodies have come in the form of amateur videos on Tetris or Ghosts and Goblins, such as those of Mega 64.

These are identical twins with opposite features, that is one may be right handed and the other may be left handed; hair will whorl in the opposite direction, and so on. The success of Penny Arcade has attracted many people in the industry, including Ubisoft. Some percentage of monozygotic twins are called "mirror twins" or mirror image twins. Here, the storylines or jokes revolve around current events in video gaming. (Fraga, et al., 2005). The other is a more traditional comic strip, containing original art, like Penny Arcade. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference. Sometimes these are original stories, but are often parodies of the game in which the sprite came from.

50-year-old twins had over 3 times the epigenetic difference that the 3-year-old twins had. The first one is the sprite comic, such as 8 Bit Theatre, in which the artist uses sprites from the earlier Final Fantasy games to tell stories. The number of differences between identical twins increases with age. Currently there are two varieties. A study of 80 pairs of twins ranging in age from 3 to 74 showed that the youngest twins have relatively few epigenetic differences. On the Internet, gaming has also become a popular subject of many webcomics. This is called epigenetic modification. Also, video games have found themselves on MTV2, in a popular show called Video Mod, where characters from popular video games perform songs from hit artists, such as characters from The Sims 2 performing the song "Stacy's Mom" by Fountains Of Wayne.

Identical twins have identical DNA but differing environmental influences throughout their lives affect which genes are switched on or off. Some examples of this are the Catwoman and King Arthur movie games along with the entire television-to-game franchise. There are usually obvious signs of differences when the identical twins are observed separately or together. Some publishers believe that the success of the movie will help the game sell, and so may not have as lengthy a development schedule as needed to make a compelling game. Twins are unique individuals that establish their own individual likes and dislikes. Even though movies have had more success in game conversion, not all movie games are popular amongst the gaming community. Many identical twins spend most of their time together (especially as children), so people often assume that they will behave alike just as they look alike; however, this is not the case. Most summer blockbuster films now have a simultaneous video game release; some of the most lucrative video games of recent times are based on movies, such as Electronic Arts' and Stormfront Studios' The Lord of the Rings: The Two Towers and the series of EA LotR games that followed it, and Activision's two Spider-Man movie games.

They develop their own individual personalities to enable themselves to be identified as individual persons. Movies have had far more success moving the other direction, onto video games. Identical twins can behave as differently as any other siblings (a matter of much interest to psychologists). Sometime, they even "help" more obscure/Japan-only games pick up popularity in America although rarely; To Heart would be the best example of such thing. The exact cause for the splitting of a zygote or embryo is unknown. cartoons, Sonic SatAM, Captain N: The Game Master and Earthworm Jim while Sonic Underground, the American Mega Man cartoon and 4Kids Entertainment's dubs (although this isn't limited to their video game-based dubs) are cited as being poor. While it was originally thought that identical twins do not run in families, but occur more or less randomly, some recent research has suggested that a genetic predisposition may exist. Some notable examples of major success includes the various Mario Bros.

As they mature, identical twins often become less alike because of lifestyle choices or external influences such as scars. On the other hand, video games get much more success when adapted into cartoons/anime. Examination of details such as fingerprints can tell them apart. The recently released Final Fantasy VII: Advent Children may change some people's minds though, even though it's a straight to DVD affair. (On extremely rare occasions, an original XXY zygote may form monozygotic boy/girl twins by dropping the Y chromosome for one twin and the extra X chromosome for the other.) Monozygotic twins generally look alike, although sometimes they appear as mirror images of each other. Films like Final Fantasy: The Spirits Within, which has received mixed responses from audiences, with some saying it is a great movie, and others saying it is a very bad movie with excellent computer-generated imagery, but ultimately flopped in the box office, and Uwe Boll's House of the Dead and Alone in the Dark, which both ended up being horrible flops both in fan reactions and box office success and both ending up on the IMDB's bottom 100 movies, do not, in turn, give much confidence in whether these movies will be handled seriously. Monozygotic twins are genetically identical unless there has been a mutation in development, and they are almost always the same gender. There is still debate in the movie industry on whether video games can consistently be turned into good, profitable movies.

About 50% of mono-mono twins die from umbilical cord entanglement. John Woo also has producing rights on a movie based on the popular Nintendo game Metroid. These twins may develop such that blood passes disproportionately from one twin to the other through connecting blood vessels within their shared placenta, leading to twin-to-twin transfusion syndrome. Doom, a game which film makers were trying to cross over since the mid '90s, finally hit theatres 12 years after its initial release. Monochorionic twins, sharing one placenta, usually also share the placental blood supply. However, after the initial bunch, many projects materialized that were never finished, but the success of films like Lara Croft: Tomb Raider has led to more films materializing. For example, the umbilical cords of monoamniotic twins can become entangled, reducing or interrupting the blood supply to the developing fetus. Despite the ultimately poor performance of these movies, many studios still want to turn big games into movies, hoping that the popularity of the game will help the movie.

Sharing the same amnion (or the same amnion and placenta) can cause complications in pregnancy. Reviews have generally been poor. Twinning after 12 days post-fertilization will typically result in conjoined twins. In the mid-90s, films for Super Mario Brothers, Street Fighter, Wing Commander and Mortal Kombat were released. Twinning between 8 to 12 days after fertilization will usually result in monochorionic-monoamniotic ("mono-mono") twins. One of the first films based on a video game property was The Wizard, which some criticized as a 90-minute ad for Super Mario Brothers 3. Twinning between 4 to 8 days after fertilization typically results in monochorionic-diamniotic ("mono-di") twins. Video game properties have had mixed success when migrating to the movies.

Zygotes that twin at the earliest stages will be diamniotic and dichorionic ("di-di"). Many T-shirts are available that directly reference video games, such as one with a picture of an NES controller with the text 'Know Your Roots.' Also, video games have also become a major part in cross marketing platforms, such as in Pokémon or Yu-Gi-Oh, where a child can watch the television show, buy the trading cards, and play the various video games available. The later in pregnancy that twinning occurs, the more structures will be shared. Video gaming is now ingrained in popular culture in the United States. This condition does not occur for fraternal twins. PlayStation Magazine, GamePro, GameSpot, GameSpy, IGN, Amped News, and GameFAQs. Also note that any monochorionic or monoamniotic twins are identical twins. Numerous websites and publications devoted solely to games have been created, including Official Xbox Magazine, Nintendo Power, Official U.S.

All monoamniotic twins are monochorionic. The success of computer and online gaming there is usually credited to South Korea's push for broadband Internet connections in the home and earlier bans on Japanese products (these restrictions were removed by the late 1990s). Diamniotic identical twins may share the same placenta (known as monochorionic) or not (dichorionic). StarCraft gosu (expert players) are celebrities in a game that some have called the country's national sport. Depending on the stage at which the zygote divides, identical twins may share the same amnion (in which case they are known as monoamniotic) or not (diamniotic). Developers there boast MMORPGs such as Lineage and Ragnarok Online with millions of subscribers and a third of the world's MMOG revenue. The two embryos develop into fetuses sharing the same womb. Take for example South Korea.

Identical twins occur when a single egg is fertilized to form one zygote (monozygotic) but the zygote then divides into two separate embryos. Computer games are huge business worldwide. However, it is only the female that has any influence on the chances of having fraternal twins as the male cannot make her release more than one ovum. A large number of summer blockbuster films spawn a companion game, often launching at the same time in order to share the marketing costs. Studies show that there is a genetic basis for fraternal twinning—that is, non-identical twins do run in families. The game and film industries are also becoming increasingly intertwined, with companies like Sony having significant stakes in both. Dizygotic twins may be a different sex or the same sex, just as with any other siblings. This is untrue; in the United States, video game sales have exceeded the movies' total box office revenue each year since about 1996, but the movie studios trounce the video game publishers when the movies' "ancillary revenue" is counted, meaning sales of DVDs, sales to foreign distributors, and sales to cable TV, satellite TV, and broadcast television networks.

Dizygotic twins, like any siblings, have a very small chance of having the exact same chromosome profile, but most likely have a number of different chromosomes that distinguish them. There is a commonly repeated, mistaken belief that video game sales now exceed the revenues of the movie industry. The two eggs form two zygotes, and these twins are therefore also known as dizygotic as well as "biovular" twins. Retail PC game sales have been declining slightly each year since about 1998, but this fact should be taken with a grain of salt: the retail sales numbers from NPD do not include sales from online downloads, nor subscription revenue for games like MMORPGs. Fraternal twins (commonly known as "non-identical twins") usually occur when two fertilized eggs are implanted in the uterine wall at the same time. These figures are sales in dollars, not units; unit shipments for each category were higher than the dollar sales numbers indicate, as more software and hardware was sold at reduced prices compared to 2003. . It reported that as of 2004:.

Since some premature births often have health consequence to the babies, twins birth are often handled with special procedures. The NPD Group tracks computer and video game sales in the United States. Due to the limited size of the mother's womb, multiple pregnancy is much less likely to carry to full term than singleton birth (twins usually around 34 to 36 weeks). In South Korea, computer games are preferred, especially MMORPG games and real-time strategy games; there are over 20,000 PC bang Internet cafes where computer games can be played for an hourly charge. A fetus alone in the womb is called a singleton. Japanese consumers avoid computer games and instead buy video games, with a strong preference for games created in Japan, that run on Japanese consoles (1 reason the Xbox series is less popular). The term twin most notably refers to two individuals (or one of two individuals) who have shared the same uterus (womb) and are usually, but not necessarily, born on the same day. Sales of different types of games vary widely between these markets due to local preferences.

Several previous pregnancies. [3]. Greater than average height and weight. China is not considered a significant market, most likely because an estimated 95% of video games sold in the country are pirated. Between the age of 30 and 40 years. Other significant markets include Spain, Germany, South Korea, France, and Italy. She is of African descent. The four largest markets for computer and video games are the United States, Japan, Canada and the United Kingdom.

The average age of the video game player is now 30 [2], belying the myth that video games are largely a diversion for teenagers. The popularity of computer and video games, as a whole, has been increasing steadily ever since the 1984-1987 drop-off caused by the video game crash of 1983, and the popularity appears to be continuing to increase. This term has now expanded to include any game that has more direct action, with fewer long term objectives, focuses on time limits and, for the most part, shorter in-game levels. Arcade games that are no longer profitable to lease can be purchased by private individuals, many of whom then explore the game dynamics by altering the programs in minor ways.

Controls are similar to those available for many consoles (albeit usually as peripherals) and range from the classic joystick and buttons (Pac-Man), to light guns (Duck Hunt), to pads on the ground that sense pressure (Dance Dance Revolution). These are programmed, equipped, and decorated for a specific game, consisting of a video display, a set of controls, and the coin slot. Arcade games, traditionally, are "coin-operated games", played on a standalone device originally leased to commercial entertainment venues. Because they are designed to be played on the go, they were traditionally small enough to carry conveniently in a bag or jacket (the Virtual Boy being an exception to this), but due to their small size, handheld consoles have reduced processing power compared to larger consoles, meaning that games are shorter, and until the release of the Nintendo DS, were largely limited to 2D.

Handheld consoles act as their own controllers, which the player uses to interact with the game, as well as having in-built display and audio output devices. Handheld games are played on handheld game consoles, such as the Nintendo Game Boy line, the Nintendo DS and the Sony PSP. Consoles themselves branched off from personal computers around two decades ago, a fact which is still evident not only in the name, but also in many of the peripherals available for many consoles, like the keyboard and mouse peripherals released for the Sony PlayStation 2 and the Sega Dreamcast. The player usually interacts with the game through a controller, and video and sound are typically delivered to the player via a television through composite A/V cables, although most modern consoles support additional outputs, such as surround sound, progressive scan, and High Definition setups through the use of component cables.

Console games are played on a video game console,or "home console", a specialized computer specifically designed to play games of a certain format. Some of these games, such as Runescape, however, have expanded far beyond this, and can often be considered on the same level as "mainstream" PC games. Some are on going user-based games that have no ending. These games generally do not share the same magnitude of development costs, depth, or seriousness of PC and console games, and are generally quick to complete by comparison.

The Internet is also host to thousands of small web-based games, written using formats like Flash and Javascript. Online games need to allow several people to play at the same time, so not all genres are suitable; the most popular genres include MMORPGs, FPSs, racing/driving games, strategy games, and sports titles. It is now a key feature of modern games, with the inclusion of Internet connectivity in consoles such as the PlayStation 2, Xbox and Gamecube (although it was only fully exploited on the Xbox); portable consoles such as the PSP or DS that use Wi-Fi, and in mobile/cellular phones. The first console to incorporate this feature was the Sega Dreamcast.

Online gaming began with PC games, but has expanded over time to include most modern consoles. Online Games are those which are played over the Internet. Ease of software piracy is also a much greater threat with PC games, although console hardware modifications do make it possible to play pirated games on them as well. Without the proper hardware, the game may perform poorly or not run at all, as opposed to console software, in which the software is designed based on the set hardware configuration of the console.

One possible explanation for the declining sales of personal computer games in relation to that of consoles can be found within the PC itself: a computer must meet certain minimum requirements such as CPU speed, Random access memory (RAM), system clock speed (MHz or GHz), video card memory, hard drive space, operating system, Internet connection speed (for online games) and other criteria. For more information, see sales. According to the Entertainment Software Association, console games have outsold computer games roughly four units to one in 2003 and 2004 [1]. There is, however, a continuing movement to get the most popular games to run under the Mac and Linux operating systems, although it is still small.

Today, most major PC games require a recent version of the Windows operating system to be installed on the computer. PC games are often more detailed than console games because of early market releases of their external architecture and graphics cards. Video feedback is received by the user through the computer screen, sound through speakers or headphones. They are played on the personal computer with standard computer interface devices such as the keyboard and mouse, or additional peripherals, such as joysticks.

Personal computer games are commonly referred to as "computer games" or "PC games". During the last generation of gaming, most major PC game releases have coincided with the release of console versions, and titles initially developed for a single platform are often ported to others if they prove to be successful. Many games intended for PCs are now just as prevalent on consoles, with many developers creating versions for more than one platform. The final home platform is the PC.

The 3 main home video game platform companies are Nintendo, Microsoft, and Sony, who between them have created seven of the eight home platforms most commonly used today. Games are not interchangeable between platforms so, for example, Xbox games will not work in your PC. Personal computers, consoles, handheld systems, and arcade machines are all common. Today there are many different devices, or platforms, on which games may be played.

The increase in the popularity of online gaming has also resulted in sub-genres being formed, such as massively multiplayer online role-playing game (MMORPG). Most games nowadays are a combination of two or more genres (e.g action/RPG). The most common genres in use today include platformer, adventure, role-playing game (RPG), first person shooter (FPS), third person shooter (both these are sometimes refered to as shoot-'em-ups), sports, racing, fighting, action (note that this term is abused often), puzzle, simulation, and real time strategy (RTS). Games, like most other forms of media, may be categorized into genres based on gameplay, atmosphere, and various other factors.

Although the use of this term is often disputed, as it is considered too vague for the range of concepts it describes, it is currently the most commonly used and accepted term for this purpose when describing video games. It includes direct interaction, such as controls and interface, but also design aspects of the game, such as levels and graphics. In computer and video gaming, gameplay (sometimes called "Game mechanics") is a general term that describes player interaction with a game. The Xbox 360, will be powered by a multi-core CPU, the PlayStation 3 will be powered by Cell processor technology, and the Nintendo Revolution will allow the gamer to interact with the game via a wireless motion sensing controller and promises more innovations, although full technical specifications are yet to be revealed.

Sony with the PlayStation 3 and Nintendo with the codenamed Revolution will join Microsoft with the already released Xbox 360 in this year's "technology race". 2006 will see the continuation of the next generation of console gaming in the form of two new consoles. The end of 2005 saw the release of the Xbox 360 - the first of the next generation of consoles. In Western countries the consoles have had similar levels of success (PSP sales are slightly higher), but in Japan the DS has been a huge hit, vastly outselling the PSP.

The Nintendo DS is a highly innovative handheld, the PSP is much more powerful and also includes limited media capabilities. The other two more technically advanced handhelds to be released in 2004, the Nintendo DS (DS stands for Dual-Screen) and the PlayStation Portable (PSP), didn't help the N-Gage. In 2004 Nokia released a re-designed N-Gage, called the N-Gage QD, which didn't fare much better. It was criticised for being poorly designed, and flopped.

Nokia entered the handheld market with its N-Gage game-phone hybrid in 2003. Sega realised they could no longer compete, and announced they would discontinue the Dreamcast and no longer manufacture hardware, becoming a third-party developer in 2002. Nintendo released their successor to the Nintendo 64, the GameCube, and the first all new Game Boy since the consoles inception, the Game Boy Advance. Its flagship game, Halo: Combat Evolved, is also available at the system's launch.

In 2001 Microsoft entered the videogame console industry by releasing its new home console, the Xbox. It was an instant hit and became the best-selling computer game of all time, surpassing Myst. The Sims was also released. In 2000 Sony released the widely anticipated PlayStation 2.

1998 saw the releases of the Sega Dreamcast in Japan (1999 in the US) and the Game Boy Color from Nintendo. The Saturn was successful in Japan but a failure in North America, leaving Sega outside of the main competition. By the end of this period, Sony had dethroned Nintendo, the PlayStation outselling the Nintendo 64. In particular, SquareSoft, which had released all previous games in its Final Fantasy series for Nintendo consoles, now turned to the PlayStation; Final Fantasy VII (1997) was a huge success, establishing the popularity of role-playing games in the west and making the PlayStation the primary console for the genre.

Nintendo's choice to use cartridges instead of CD-ROMs for the Nintendo 64, unique among the consoles of this period, proved to have negative consequences. The flagship title, Super Mario 64, became a defining title for 3D platform games. After many delays, Nintendo released its 64-bit console, the Nintendo 64 in 1996, selling more than 1.5 million units in only three months. Both consoles used 32-bit technology; the door was open for 3D games.

In 1994-1995, Sega released Sega Saturn and Sony made its debut to the video gaming scene with the PlayStation. Basic 3D graphics entered the mainstream with flat-shaded polygons enabled by additional processors in game cartridges like Virtua Racing and Starfox. CD-ROM drives were first seen in this generation, as add-ons for the PC Engine in 1988 and the Megadrive in 1991. The PC Engine eventually lost out to the Super Famicom, but retained enough of a user base to support new games well into the late 1990s.

In Japan, the PC Engine's (Turbografx 16) 1987 success against the Famicom and CD drive peripheral allowed it to fend off the Mega Drive (Genesis) in 1988, which never really caught on to the same degree as outside Japan. The NEC TurboGrafx 16 was the first 16-bit system to be marketed in the region, but did not achieve a large following, partly due to a limited library of English games and effective marketing from Sega. The North American market was dominated by the Sega Genesis early on after its debut in 1989, with the Nintendo Super NES proving a strong, roughly equal rival in 1991. While some of the other systems remained in production until the mid-90s, the Game Boy remained at the top spot in sales throughout its lifespan.

Several rival handhelds also made their debut around that time, including the Sega Game Gear and Atari Lynx. Included with the system was Tetris, which became a popular puzzle game. In 1989, Nintendo released the Game Boy, the first popular handheld console. See the article on Console wars for additional information on that facet of game history.

The last two decades of game history have been marked by separate markets for games on video game consoles, home computers and handhelds. and many others of today's popular Nintendo genre. The video game crash of 1983, however, produced a dark age in the market that was not filled until the Nintendo Entertainment System (NES) reached North America in 1985.This presented Americans with games such as Mario Bros. The late 1970s to early 1980s brought about the improvement of home consoles and the release of the Atari 2600, Intellivision and Colecovision.

He created a system with limited capabilities called the Magnavox Odyssey, which paved the way for the next wave of home consoles. The first home console video games, were created by Ralph Baer who is now known as the creator of video games. The 1970s also saw the release of the first home video game consoles. The paddles were white bars with a dot moving between them.

One of the best-known of these games is Pong, a simple game simulating Ping Pong. Arcade games were developed in the 1970s (Pac-man to Frogger) and led to the so-called "Golden Age of Arcade Games". The first video game was Tennis for Two created by William Higginbotham in 1958. The first primitive computer and video games were developed in the 1960s and 1970s and ran on platforms such as oscilloscopes, university mainframes and EDSAC computers.

. In common usage, "computer game" or "PC game" refers specifically to games played on a personal computer, "console game" refers to games played on specifically-designed set top box, that play through a TV and "video game" (or "videogame") refers to any game played on a device that plays through your TV but also includes PC, Console, Mobile Phone or PDA or other handheld device. To avoid ambiguity, this game software is referred to as "computer and video games" throughout this article, which explores things common to both types of game. The phrase interactive entertainment is the formal reference to computer and video games.

Usually there are rules and goals, but in more open-ended games the player may be free to do whatever they like within the confines of the virtual universe. These terms are not always interchangeable as some games, particularly older games, do not use a video display. A video game is a computer game where a video display such as a monitor or television is the primary feedback device. A computer game is a computer-controlled game that players may interact with.

PC game sales: $1.1 billion, down 2% from 2003 [6]. Console and portable hardware and accessory sales: $3.7 billion, down 35% from 2003 [5]. Console and portable software sales: $6.2 billion, up 8% from 2003 [4]. For specific information regarding "console games" or, see console game..

For specific information regarding "computer games", see personal computer game..

08-04-15 FTPPro Support FTPPro looks and feels just like Windows Explorer Contact FTPPro FTPPro Help Topics FTPPro Terms Of Use ftppro.com/browse2000.php Business Search Directory Real Estate Database WebExposure.us Google+ Directory Dan Schmidt is a keyboardist, composer, songwriter, and producer.