Topaz

Topaz is also the birthstone of November. 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. According to Rebbenu Bachya, the word "Leshem" in the verse Exodus 28:19 means "Topaz" and was the stone on the Ephod representing the tribe of Dan. Multiple births are common in many animal species, such as cats, sheep, and ferrets. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above. 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. The name "topaz" is derived from the Greek topazos, "to seek," which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be a yellowish olivine) was mined in ancient times. When monozygotic twins are born with different genders it is because of chromosomal birth defects.

It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States. 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. Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. Among monozygotic twins, in extremely rare cases, twins have been born with opposite sexes (one male, one female). A recent trend in jewelry is the manufacture of topaz specimens that display iridescent colors, by applying a thin layer of titanium oxide via physical vapor deposition. 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. It can also be irradiated, turning the stone a light and distinctive shade of blue. This can lead to the possibility of a woman carrying fraternal twins with different fathers (that is, half-siblings).

When heated, yellow topaz often becomes reddish-pink. 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). They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. 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. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. 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. Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. Twin studies are studies that assess identical (monozygotic) twins for medical, genetic, or psychological characteristics to try to isolate genetic influence from environmental influence.

The fracture is conchoidal to uneven. Many fertility treatments have no effect on the likelihood of multiple births. It has an easy and perfect basal cleavage and so gemstones or other fine specimens should be handled with care to avoid developing cleavage flaws. Some other treatments such as the drug Clomid can stimulate a woman to release multiple eggs, allowing the possibility of multiples. It crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. With in vitro fertilisation (IVF), this is primarily due to the insertion of multiple embryos into the uterus. The mineral topaz is a silicate of aluminium and fluorine with the chemical formula Al₂SiO₄(F,OH)₂. This can vary depending on what types of fertility treatments are used.

This article is about the mineral or gemstone, for other uses see: Topaz (disambiguation).. Women undergoing certain fertility treatments may have a greater chance of multiple births. Mineral galleries. Dizygotic twin pregnancies are slightly more likely when the following factors are present in the woman:. Mindat with location data. Some evidence suggests that the environment of the womb causes the zygote to split in most cases. Webmineral. 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).

The cause of monozygotic twinning is unknown. 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. 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. If there are three, they are called triplets; four, quadruplets; five, quintuplets; six, sextuplets, seven, septuplets, and so on.

Sometimes multiple births may involve more than two fetuses. 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.