Twin Wikipedia. Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic identical, meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic fraternal, meaning that they develop from two different eggs. In fraternal twins, each twin is fertilized by its own sperm cell. In contrast, a fetus that develops alone in the womb is called a singleton, and the general term for one offspring of a multiple birth is multiple. Non related look alikes whose resemblance parallels that of twins are referred to as doppelgangers. StatisticseditThe human twin birth rate in the United States, rose 7. The Yoruba have the highest rate of twinning in the world, at 4. I/41bVrusQX1L.jpg' alt='Creasy Maternal Fetal Medicine Pdf File' title='Creasy Maternal Fetal Medicine Pdf File' />In Central Africa there are 1. In Latin America, South Asia, and Southeast Asia, the lowest rates are found only 6 to 9 twin sets per 1,0. North America and Europe have intermediate rates of 9 to 1. Multiple pregnancies are much less likely to carry to full term than single births, with twin pregnancies lasting on average 3. Women who have a family history of fraternal twins have a higher chance of producing fraternal twins themselves, as there is a genetically linked tendency to hyper ovulate. There is no known genetic link for identical twinning. Other factors that increase the odds of having fraternal twins include maternal age, fertility drugs and other fertility treatments, nutrition, and prior births. Types of twins and zygosityeditThe vast majority of twins are either dizygotic fraternal or monozygotic identical. HLAG histocompatibility antigen, class I, G, also known as human leukocyte antigen G HLAG, is a protein that in humans is encoded by the HLAG gene. Less common variants are discussed further down the article. Twins can be Female femalesometimes called sororal twins. Male male twinsno special name. Malefemale twinsmost common pairing half of all fraternal dizygotic twins are male female. Among non twin births, male singletons are slightly about five percent more common than female singletons. The rates for singletons vary slightly by country. For example, the sex ratio of birth in the US is 1. Italy. 1. 6 However, males are also more susceptible than females to die in utero, and since the death rate in utero is higher for twins, it leads to female twins being more common than male twins. Zygosity is the degree of identity in the genome of twins. Common name. Scientific name. Zygosity. Development. Occurrence. Identification. Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic identical, meaning that they develop from one zygote, which splits and. Health. Otheridenticalmonozygoticxxxxxxfraternaldizygoticxxxxxxhalf identicalxxxxxxxmirror imagexxxxxxxmixed chromosomexxxxxxxsuperfecundationxxeggs are fertilized during different acts of intercoursexxxusage is practically equivalent with Heteropaternal Superfecundation, which occurs when two different males father fraternal twins, because though superfecundation by the same father is thought to be a common occurrence, it can only be proven to have occurred with multiple fathers. Dizygotic fraternal twinsedit. Eight month old sororal twins napping. Dizygotic DZ or fraternaltwins also referred to as non identical twins, dissimilar twins, biovular twins, and, informally in the case of females, sororal twins usually occur when two fertilized eggs are implanted in the uterus wall at the same time. When two eggs are independently fertilized by two different sperm cells, fraternal twins result. The two eggs, or ova, form two zygotes, hence the terms dizygotic and biovular. Fraternal twins are, essentially, two ordinary siblings who happen to be born at the same time, since they arise from two separate eggs fertilized by two separate sperm, just like ordinary siblings. This is the most common type of twin. Dizygotic twins, like any other siblings, have an extremely small chance of having the same chromosome profile. Even if they happen to have the same chromosome profile, they will always have different genetic material on each chromosome, due to chromosomal crossover during meiosis. Siri Download For Iphone 4 Cydia Unlock. Like any other siblings, dizygotic twins may look similar, particularly given that they are the same age. However, dizygotic twins may also look very different from each other. Studies show that there is a genetic proclivity for dizygotic twinning. However, it is only the mother who has any effect on the chances of having such twins there is no known mechanism for a father to cause the release of more than one ovum. Dizygotic twinning ranges from six per thousand births in Japan similar to the rate of monozygotic twins to 1. African countries. Dizygotic twins are also more common for older mothers, with twinning rates doubling in mothers over the age of 3. With the advent of technologies and techniques to assist women in getting pregnant, the rate of fraternals has increased markedly. Monozygotic identical twinsedit. Comparison of zygote development in monozygotic and dizygotic twins. In the uterus, a majority of monozygotic twins 6. In 1. 83. 0 of monozygotic twins each fetus has a separate placenta and a separate amniotic sac. A small number 12 of monozygotic twins share the same placenta and amniotic sac. Fraternal twins each have their own placenta and own amniotic sac. Monozygotic MZ or identicaltwins occur when a single egg is fertilized to form one zygote hence, monozygotic which then divides into two separate embryos. MechanismeditRegarding spontaneous or natural monozygotic twinning, a recent theory proposes that monozygotic twins are formed after a blastocyst essentially collapses, splitting the progenitor cells those that contain the bodys fundamental genetic material in half, leaving the same genetic material divided in two on opposite sides of the embryo. Eventually, two separate fetuses develop. Spontaneous division of the zygote into two embryos is not considered to be a hereditary trait, but rather a spontaneous and random event. Monozygotic twins may also be created artificially by embryo splitting. It can be used as an expansion of in vitro fertilization IVF to increase the number of available embryos for embryo transfer. IncidenceeditMonozygotic twinning occurs in birthing at a rate of about 3 in every 1. The likelihood of a single fertilization resulting in monozygotic twins is uniformly distributed in all populations around the world. This is in marked contrast to dizygotic twinning, which ranges from about six per thousand births in Japan almost similar to the rate of identical twins, which is around 45 to 1. India2. 3 and up to over 2. Central African countries. The exact cause for the splitting of a zygote or embryo is unknown. IVF techniques are more likely to create dizygotic twins. For IVF deliveries, there are nearly 2. Genetic and epigenetic similarityeditMonozygotic twins are genetically nearly identical and they are always the same sex unless there has been a mutation during development. The children of monozygotic twins test genetically as half siblings or full siblings, if a pair of monozygotic twins reproduces with another pair or with the same person, rather than first cousins. Identical twins do not have the same fingerprints, because even in the confines of the womb, the fetuses touch different parts of this environment, which gives small variations in the same fingerprint, making them unique. Monozygotic twins always have different phenotypes. Normally due to an environmental factor or the deactivation of different X chromosomes in female monozygotic twins, and in some extremely rare cases, due to aneuploidy, twins may express different sexual phenotypes, normally from an XXY Klinefelter syndrome zygote splitting unevenly. Monozygotic twins, although genetically very similar, are not genetically exactly the same. The DNA in white blood cells of 6. Polymorphisms appeared in 2 of the 3. DNA sequence difference for every 1. The mutations producing the differences detected in this study would have occurred during embryonic cell division after the point of fertilization. If they occur early in fetal development, they will be present in a very large proportion of body cells.