Twin

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. Typically, one neighbour cannot alter the common wall if it is likely to affect the building or property on the other side. Multiple births are common in many animal species, such as cats, sheep, and ferrets. Special laws often govern walls shared by neighbouring properties. 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. A dike is one type of retaining wall, as is a levee. When monozygotic twins are born with different genders it is because of chromosomal birth defects. The ground surface or water on one side of a retaining wall will be noticeably higher than on the other side.

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. Retaining walls are a special type of wall, that may be either external to a building or part of a building, that serves to provide a barrier to the movement of earth, stone or water. Among monozygotic twins, in extremely rare cases, twins have been born with opposite sexes (one male, one female). In areas of rocky soils around the world, farmers (and their slaves, as in the United States before slavery was abolished) have often pulled large quantities of stone out of their fields to make farming easier, and have stacked those stones to make walls that either mark the field boundary, or the property boundary, or both. 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. Extreme examples of boundary walls include the Great Wall of China and Hadrian's Wall. This can lead to the possibility of a woman carrying fraternal twins with different fathers (that is, half-siblings). Since they are no longer relevant for defense, the cities have grown beyond their walls, and many of the walls have been torn down.

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). In fact, the English word "wall" is derived from Latin "vallum, which was a type of fortification wall. 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. Before the invention of artillery, many European cities had protective walls. 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. the Berlin Wall or the Israeli West Bank barrier. Twin studies are studies that assess identical (monozygotic) twins for medical, genetic, or psychological characteristics to try to isolate genetic influence from environmental influence. A common term for both is barrier, convenient if it is partly a wall and partly a fence, e.g.

Many fertility treatments have no effect on the likelihood of multiple births. More to the point, if an exterior structure is made of wood or wire, it is generally referred to as a fence, while if it is made of masonry, it is considered a wall. Some other treatments such as the drug Clomid can stimulate a woman to release multiple eggs, allowing the possibility of multiples. These intergrade into fences; the conventional differentiation is that a fence is of minimal thickness and often is open in nature, while a wall is usually more than a nominal thickness and is completely closed, or opaque. With in vitro fertilisation (IVF), this is primarily due to the insertion of multiple embryos into the uterus. Boundary walls include privacy walls, boundary-marking walls, and city walls. This can vary depending on what types of fertility treatments are used. On a ship, the walls separating compartments are termed ' Bulkheads', whilst the thinner walls separating cabins are termed 'Partitions'.

Women undergoing certain fertility treatments may have a greater chance of multiple births. Building walls frequently become works of art, such as when murals are painted on them. Dizygotic twin pregnancies are slightly more likely when the following factors are present in the woman:. Electrical outlets are usually mounted in walls. Some evidence suggests that the environment of the womb causes the zygote to split in most cases. In addition, the wall may house various types of electrical wiring or plumbing. 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). In today's construction, a building wall will usually have the structural elements (such as 2×4 studs in a house wall), insulation, and finish elements, or surface (such as drywall or panelling).

The cause of monozygotic twinning is unknown. Such walls most often have three or more separate components. 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. Building walls have two main purposes: to support roofs and ceilings, and to divide space, providing security against intrusion and weather. 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. There are three principal types of structural walls: building walls, exterior boundary walls, and retaining walls. If there are three, they are called triplets; four, quadruplets; five, quintuplets; six, sextuplets, seven, septuplets, and so on. Most commonly, a wall separates space in buildings into rooms, or protects or delineates a space in the open air.

Sometimes multiple births may involve more than two fetuses. A wall is a usually solid structure that defines and sometimes protects an area. 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. Thus, approximately 6% of children born in the US in 2001 were twins. In 2001, for the first time ever in the US, the twinning rate exceeded 3% of all births.

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 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, about 1 in 80 human births (1.2%) has been the result of a twin pregnancy. Similar to vanishing 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. 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. 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. Sometimes the parasitic twin just becomes an almost indistinguishable part of the other.

One fetus acts as a parasite towards the other. Sometimes one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. This condition occurs in about 1 in 100,000 pregnancies. This occurs where the single zygote of identical twins fails to separate completely.

Conjoined twins are monozygotic twins, whose bodies are joined together at birth. Early obstetric ultrasonography exams sometimes reveal an "extra" fetus, which fails to develop and instead disintegrates and vanishes. Researchers suspect that more pregnancies start out as multiples than come to term that way. Such conditions are usually associated with a higher incidence of other birth defects.

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). One mirror may or may not have situs inversus. They result from a late split of the fertilized egg at around 9-12 days. The incidence of mirror twinning is comparatively rare.

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. Some percentage of monozygotic twins are called "mirror twins" or mirror image twins. (Fraga, et al., 2005). Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference.

50-year-old twins had over 3 times the epigenetic difference that the 3-year-old twins had. The number of differences between identical twins increases with age. A study of 80 pairs of twins ranging in age from 3 to 74 showed that the youngest twins have relatively few epigenetic differences. This is called epigenetic modification.

Identical twins have identical DNA but differing environmental influences throughout their lives affect which genes are switched on or off. There are usually obvious signs of differences when the identical twins are observed separately or together. Twins are unique individuals that establish their own individual likes and dislikes. 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.

They develop their own individual personalities to enable themselves to be identified as individual persons. Identical twins can behave as differently as any other siblings (a matter of much interest to psychologists). The exact cause for the splitting of a zygote or embryo is unknown. 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.

As they mature, identical twins often become less alike because of lifestyle choices or external influences such as scars. Examination of details such as fingerprints can tell them apart. (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. Monozygotic twins are genetically identical unless there has been a mutation in development, and they are almost always the same gender.

About 50% of mono-mono twins die from umbilical cord entanglement. 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. Monochorionic twins, sharing one placenta, usually also share the placental blood supply. For example, the umbilical cords of monoamniotic twins can become entangled, reducing or interrupting the blood supply to the developing fetus.

Sharing the same amnion (or the same amnion and placenta) can cause complications in pregnancy. Twinning after 12 days post-fertilization will typically result in conjoined twins. Twinning between 8 to 12 days after fertilization will usually result in monochorionic-monoamniotic ("mono-mono") twins. Twinning between 4 to 8 days after fertilization typically results in monochorionic-diamniotic ("mono-di") twins.

Zygotes that twin at the earliest stages will be diamniotic and dichorionic ("di-di"). The later in pregnancy that twinning occurs, the more structures will be shared. This condition does not occur for fraternal twins. Also note that any monochorionic or monoamniotic twins are identical twins.

All monoamniotic twins are monochorionic. Diamniotic identical twins may share the same placenta (known as monochorionic) or not (dichorionic). 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). The two embryos develop into fetuses sharing the same womb.

Identical twins occur when a single egg is fertilized to form one zygote (monozygotic) but the zygote then divides into two separate embryos. 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. Studies show that there is a genetic basis for fraternal twinning—that is, non-identical twins do run in families. Dizygotic twins may be a different sex or the same sex, just as with any other siblings.

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. The two eggs form two zygotes, and these twins are therefore also known as dizygotic as well as "biovular" 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. .

Since some premature births often have health consequence to the babies, twins birth are often handled with special procedures. 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). A fetus alone in the womb is called a singleton. 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.

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