Zygote development between identical twins-HIE Multimedia - Formation of twins

There are two types of twins: identical also called monozygotic, abbreviated MZ and fraternal also called dizygotic, abbreviated DZ. A zygote is the fertilized egg formed when a sperm combines with fertilizes an egg at conception. The zygote then starts to divide and forms an embryo. The embryo is called a fetus in later stages of prenatal before birth development. The zygote starts to develop into an embryo, but at some time during the first two weeks after conception, the developing embryo splits into two identical parts.

Zygote development between identical twins

Zygote development between identical twins

Zygote development between identical twins

But this is rare, and a gene has yet to be identified that increases the risk of monozygotic twinning. Some identical twins may be born with individual sets of membranes, which may lead to the mistaken assumption that the babies are fraternal. Possibly the worldwide record for the duration of the time gap between the first and the second Indian clits and tits was the birth of twins 97 days apart in Cologne, Germany, the first of which was born on Zygote development between identical twins 17, Are egg and sperm gametes and diploid? Thus each broken blastomere give rise to a new independent individual. The following content is displayed as Tabs. This forms twins. Both types are safe and reliable. Nevertheless, the rate of monozygotic twins remains at about 1 in across the globe.

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Reply TwinPickle November 24, at pm. At that time, future mothers only knew that they were pregnant; they did not know the sex; they did not Zygote development between identical twins whether they were carrying one, two, or more fetuses. Identical twins are monozygotic, meaning they develop in a single zygote that divides into two embryos. It is the single cell from which the entire organism will develop. Wikimedia Commons has media related to: Twin category. Reply TwinPickle January 12, at pm. This condition occurs in about 1 in 50, human pregnancies. This results in a set of twins with identical gene sequence from the mother's side, but different sequences from the father's side. Epigenetics refers to the level of activity of any particular gene. Twenty-six percent of twins were monozygotic. Asked in Biology, Genetics What is another term for identical twins? Reply TwinPickle September 26, at am. Although Zygote development between identical twins twins are more common, how do you distinguish them from Young girls with ass twins? This means the babies will share a sac and a placenta. Anna Pirhofer.

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  • The likelihood of identical twins is the same around the world — about 3 in 1,, while the incidence of fraternal twins varies by geography and ranges from 6 to over 20 per 1, deliveries.
  • Fraternal vs Identical Twins With the increased use of assisted reproductive techniques, the incidence of twins has increased in recent times.
  • Identical twins are also known as monozygotic twins, and they are fertilized when one single egg from just one zygote divides into 2 embryos, therefore they are usually the same sex, and they have very similar DNA, so to answer your question, most of the time, yes.

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The activated link is defined as Active Tab. Pelvic floor exercises are designed to improve muscle tone and prevent the need for corrective surgery It also helps to know how pregnancy may affect your emotions and feelings Adjusting to the many changes that happen around puberty can be difficult for both parents and young people New life begins when a male sex cell sperm fertilises a female egg ovum within the female reproductive system Transvaginal mesh has been used for more than 20 years to manage problems for women such as prolapse and incontinence.

While this treatment is successful for many women, some unfortunately have The menstrual cycle is complex and is controlled by many different glands and the hormones that these glands produce Some women are more at risk of amenorrhoea the absence of periods because of emotional stress or changes in weight Women who are athletes or who exercise a lot on a regular basis are at risk of developing athletic amenorrhoea, which is the absence of periods Women of any age can experience painful periods and some women find periods are no longer painful after pregnancy and childbirth The female body shows several signs of ovulation and you may experience some or all of these signs Ovulation pain is usually harmless, but can sometimes indicate various medical conditions such as endometriosis If you think you could have toxic shock syndrome, stop using tampons immediately and go to the emergency department of your nearest hospital Hormone replacement therapy HRT can reduce menopausal symptoms, but the benefits and risks need to be considered carefully The use of complementary therapies to manage menopausal symptoms is popular, but the sources of information available to consumers are of variable quality and reliability Regular weight-bearing exercise and maintaining a diet rich in calcium from childhood will help reduce bone loss at menopause Menopause, the final menstrual period, is a natural event that marks the end of a woman's reproductive years Weight gain at menopause can be managed using healthy eating and exercise; HRT may also be beneficial In Victoria, you can have two types of abortion: surgical and medication.

Both types are safe and reliable. You can have a medication abortion up to nine weeks of pregnancy. You can have a surgical Age affects the fertility of both men and women, and is the single biggest factor affecting a woman? IVF in-vitro-fertilization and ICSI intracytoplasmic sperm injection are assisted reproductive treatment ART procedures in which fertilisation of an egg occurs outside the body Whether you have a surgical or medical abortion you can become fertile again very soon after the abortion, so it's important to start using contraception immediately if you wish to prevent any The method of contraception you choose will depend on your general health, lifestyle and relationships This page shows you where to find translated information about the different methods of contraception how to prevent getting pregnant available in Australia Ectopic pregnancy is caused by a fertilised egg not being able to move through the fallopian tube Learn some facts about endometriosis.

We debunk some myths and explore symptoms, diagnosis and treatment options for women Most molar pregnancies are diagnosed when bleeding early in pregnancy prompts an ultrasound scan Placental abruption means the placenta has detached from the wall of the uterus, starving the baby of oxygen and nutrients Placenta previa means the placenta has implanted at the bottom of the uterus, over the cervix or close by An obstetric emergency may arise when a woman is pregnant, or during her delivery.

In this case, extra care is needed. A woman may need a lot of tests and treatments, and extended hospital stays. There is no evidence that pre-eclampsia is caused by emotional stress, working too hard or not getting enough rest Multiple births are more common due to the advancing average age of mothers and the rise in assisted reproductive techniques Compared with women in the healthy weight range, women who are carrying extra weight are less likely to conceive Women should become familiar with the normal look, feel and shape of their breasts, so they will notice any abnormal changes There are different types of breast cancer, and around 70 per cent are sensitive to the female sex hormone oestrogen The vast majority of breast changes are not breast cancer, but you should always see your doctor if you notice changes in your breasts Breastfeeding positioning and attachment come naturally to some babies and mothers, but many need time and practice to get it right Breast reduction surgery removes excess breast fat, glandular tissue and skin to achieve a breast size in proportion with your body Polycystic ovarian syndrome is a hormonal condition associated with irregular menstrual cycles, excess hair growth, acne, reduced fertility, and increased risk of diabetes and mood changes Salpingitis is one of the most common causes of female infertility and may permanently damage the fallopian tubes All women aged between 25 and 74 are advised to have Cervical Screening Tests every 5 years, new tests help identify HPV or cervical cancer Often, fibroids do not cause any problems, but they are occasionally associated with infertility, miscarriage and premature labour The pelvic floor and associated supporting ligaments can be weakened or damaged in many ways, causing uterine prolapse Uterine inversion means the placenta fails to detach from the uterine wall, and pulls the uterus inside-out as it exits Bacterial vaginosis BV is caused by an imbalance of the bacteria normally present in the vagina Cosmetic genital surgery involves reshaping the labia, vulva or penis to alter their size or shape Female genital cutting or circumcision FGC involves the cutting or altering of the external female genital organs Labial adhesions are more common during the nappy years, but poor hygiene may be a cause in older girls Pelvic inflammatory disease PID occurs when an infection spreads from the vagina to the cervix and fallopian tubes Some vaginal cancers have no symptoms in their early stages, and only cause symptoms once they have invaded other parts of the body A caesarean section is usually performed when it is safer for the mother or the baby than a vaginal birth Sterilisation is a permanent method of contraception that a woman can choose if she is sure that she does not want children in the future The conditions that prompt a hysterectomy can often be treated by other means, and hysterectomy should only be a last resort Puberty, menstruation, menopause, infertility, breasts, fallopian tubes, ovaries, uterus, vagina, vulva and thrush This page has been produced in consultation with and approved by: Australian Multiple Birth Association.

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I wonder if there might be a teleological explanation; in other words, might there be a purpose underlying the creation of identical twins? Fraternal twins occur due to hyper-ovulation i. Prenatal medicine. The timing of this separation determines the chorionicity the number of placentae and amniocity the number of sacs of the pregnancy. The risk of twin birth can vary depending on what types of fertility treatments are used.

Zygote development between identical twins

Zygote development between identical twins

Zygote development between identical twins. Comparison chart

The Yoruba peoples have the highest rate of twinning in the world, at 45—50 twin sets or 90— twins per 1, live births, [6] [7] [8] possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may stimulate the ovaries to release an egg from each side.

In Central Africa , there are 18—30 twin sets or 36—60 twins per 1, live births. North America and Europe have intermediate rates of 9 to 16 twin sets per 1, live births. Multiple pregnancies are much less likely to carry to full term than single births, with twin pregnancies lasting on average 37 weeks, three weeks less than full term.

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. The vast majority of twins are either dizygotic fraternal or monozygotic identical. Less common variants are discussed further down the article. 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. Zygosity is the degree of identity in the genome of twins. Dizygotic DZ or fraternal twins 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, will practically always have different sequences on each chromosome, due to chromosomal crossover during meiosis. 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 for example, be of opposite sexes. 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 14 and more per thousand in some African countries. Dizygotic twins are also more common for older mothers, with twinning rates doubling in mothers over the age of Monozygotic MZ or identical twins occur when a single egg is fertilized to form one zygote hence, "monozygotic" which then divides into two separate embryos.

Regarding spontaneous or natural monozygotic twinning, a recent theory proposes that monozygotic twins are probably formed when a blastocyst contains two inner cell masses ICM , each of which will lead to a separate fetus, rather than by the embryo splitting while hatching from the zona pellucida the gelatinous protective coating around the blastocyst. 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. Monozygotic twinning occurs in birthing at a rate of about 3 in every deliveries worldwide about 0.

The likelihood of a single fertilization resulting in monozygotic twins is uniformly distributed in all populations around the world. IVF techniques are more likely to create dizygotic twins. For IVF deliveries, there are nearly 21 pairs of twins for every 1, Monozygotic 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 however, because even within the confines of the womb, the fetuses touch different parts of their environment, giving rise to small variations in their corresponding prints and thus making them unique. Monozygotic twins always have the same phenotype. 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 66 pairs of monozygotic twins was analyzed for , single-nucleotide polymorphisms known to occur in human populations. If they occur early in fetal development, they will be present in a very large proportion of body cells.

Another cause of difference between monozygotic twins is epigenetic modification , caused by differing environmental influences throughout their lives.

Epigenetics refers to the level of activity of any particular gene. A gene may become switched on, switched off, or could become partially switched on or off in an individual. This epigenetic modification is triggered by environmental events. Monozygotic twins can have markedly different epigenetic profiles. A study of 80 pairs of monozygotic twins ranging in age from three to 74 showed that the youngest twins have relatively few epigenetic differences.

The number of epigenetic differences increases with age. Fifty-year-old twins had over three times the epigenetic difference of three-year-old twins. Twins who had spent their lives apart such as those adopted by two different sets of parents at birth had the greatest difference.

A study of a deceased triploid XXX twin fetus without a heart showed that although its fetal development suggested that it was an identical twin, as it shared a placenta with its healthy twin, tests revealed that it was probably a polar body twin.

The authors were unable to predict whether a healthy fetus could result from a polar body twinning. In , a study argued that many cases of triploidy arise from sesquizygotic semi-identical twinning. See Semi-identical Twins below, under Unusual twinnings. The degree of separation of the twins in utero depends on if and when they split into two zygotes.

Dizygotic twins were always two zygotes. Monozygotic twins split into two zygotes at some time very early in the pregnancy. The timing of this separation determines the chorionicity the number of placentae and amniocity the number of sacs of the pregnancy.

Dichorionic twins either never divided i. Monoamnionic twins divide after the first week. In very rare cases, twins become conjoined twins. Non-conjoined monozygotic twins form up to day 14 of embryonic development, but when twinning occurs after 14 days, the twins will likely be conjoined.

It is a common misconception that two placentas means twins are dizygotic. But if monozygotic twins separate early enough, the arrangement of sacs and placentas in utero is indistinguishable from dizygotic twins.

DiDi twins have the lowest mortality risk at about 9 percent, although that is still significantly higher than that of singletons. Monochorionic twins share the same placenta , and thus have a risk of twin-to-twin transfusion syndrome.

Monoamniotic twins are always monozygotic. Monoamniotic twins, as with diamniotic monochorionic twins, have a risk of twin-to-twin transfusion syndrome. Also, the two umbilical cords have an increased chance of being tangled around the babies. Because of this, there is an increased chance that the newborns may be miscarried or suffer from cerebral palsy due to lack of oxygen.

Mortality is highest for conjoined twins due to the many complications resulting from shared organs. Dichorionic-diamniotic twins at 8 weeks and 5 days since co-incubation as part of IVF. The twin at left in the image is shown in the sagittal plane with the head pointing towards upper left.

The twin at right in the image is shown in the coronal plane with the head pointing rightwards. Abdominal ultrasonography of monoamniotic twins at a gestational age of 15 weeks. There is no sign of any membrane between the fetuses. A coronal plane is shown of the twin at left, and a sagittal plane of parts of the upper thorax and head is shown of the twin at right. A study has found that insulin-like growth factor present in dairy products may increase the chance of dizygotic twinning.

Specifically, the study found that vegan mothers who exclude dairy from their diets are one-fifth as likely to have twins as vegetarian or omnivore mothers, and concluded that "Genotypes favoring elevated IGF and diets including dairy products, especially in areas where growth hormone is given to cattle, appear to enhance the chances of multiple pregnancies due to ovarian stimulation.

It may also be linked to the increase of growth hormones in food. About 1 in 90 human births 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 ".

Nevertheless, the rate of monozygotic twins remains at about 1 in across the globe. In a study on the maternity records of Hausa women living in the Savannah zone of Nigeria , there were 40 twins and 2 triplets per births.

Twenty-six percent of twins were monozygotic. The incidence of multiple births, which was about five times higher than that observed in any western population, was significantly lower than that of other ethnic groups, who live in the hot and humid climate of the southern part of the country.

The incidence of multiple births was related to maternal age but did not bear any association to the climate or prevalence of malaria. Twins are more common in African Americans. Dizygotic twin pregnancies are slightly more likely when the following factors are present in the woman:. Women undergoing certain fertility treatments may have a greater chance of dizygotic multiple births.

The risk of twin birth 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. Ovarian hyperstimulation without IVF has a very high risk of multiple birth. Reversal of anovulation with clomifene trade names including Clomid has a relatively less but yet significant risk of multiple pregnancy.

A year German study [62] of 8, vaginally delivered twins that is, 4, pregnancies in Hesse yielded a mean delivery time interval of The study stated that the occurrence of complications "was found to be more likely with increasing twin-to-twin delivery time interval" and suggested that the interval be kept short, though it noted that the study did not examine causes of complications and did not control for factors such as the level of experience of the obstetrician, the wish of the women giving birth, or the "management strategies" of the procedure of delivering the second twin.

There have also been cases in which twins are born a number of days apart. Possibly the worldwide record for the duration of the time gap between the first and the second delivery was the birth of twins 97 days apart in Cologne, Germany, the first of which was born on November 17, Researchers suspect that as many as 1 in 8 pregnancies start out as multiples, but only a single fetus is brought to full term, because the other fetus has died very early in the pregnancy and has not been detected or recorded.

There are several reasons for the "vanishing" fetus, including it being embodied or absorbed by the other fetus, placenta or the mother. This is known as vanishing twin syndrome. Also, in an unknown proportion of cases, two zygotes may fuse soon after fertilization, resulting in a single chimeric embryo, and, later, fetus.

Conjoined twins or the once-commonly used term "siamese" are monozygotic twins whose bodies are joined together during pregnancy. This occurs when the zygote starts to split after day 12 [40] following fertilization and fails to separate completely. This condition occurs in about 1 in 50, human pregnancies. Most conjoined twins are now evaluated for surgery to attempt to separate them into separate functional bodies.

The degree of difficulty rises if a vital organ or structure is shared between twins, such as the brain , heart or liver. A chimera is an ordinary person or animal except that some of their parts actually came from their twin or from the mother.

A chimera may arise either from monozygotic twin fetuses where it would be impossible to detect , or from dizygotic fetuses, which can be identified by chromosomal comparisons from various parts of the body.

The number of cells derived from each fetus can vary from one part of the body to another, and often leads to characteristic mosaicism skin coloration in human chimeras. A chimera may be intersex , composed of cells from a male twin and a female twin. In one case DNA tests determined that a woman, mystifyingly, was not the mother of two of her three children; she was found to be a chimera, and the two children were conceived from eggs derived from cells of their mother's twin.

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 becomes an almost indistinguishable part of the other, and sometimes this needs to be treated medically. A very rare type of parasitic twinning is one where a single viable twin is endangered when the other zygote becomes cancerous, or "molar".

This means that the molar zygote's cellular division continues unchecked, resulting in a cancerous growth that overtakes the viable fetus. Typically, this results when one twin has either triploidy or complete paternal uniparental disomy , resulting in little or no fetus and a cancerous, overgrown placenta, resembling a bunch of grapes.

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. This occurrence is similar to the vanishing twin syndrome, but typically occurs later, as the twin is not reabsorbed.

It is very common for twins to be born at a low birth weight. More than half of twins are born weighing less than 5. Premature birth and low birth weights, especially when under 3. Monozygotic twins who share a placenta can develop twin-to-twin transfusion syndrome. This condition means that blood from one twin is being diverted into the other twin.

One twin, the 'donor' twin, is small and anemic , the other, the 'recipient' twin, is large and polycythemic. The lives of both twins are endangered by this condition.

Stillbirths occurs when a fetus dies after 20 weeks of gestation. There are two types of stillbirth, including intrauterine death and intrapartum death. Intrauterine death occurs when a baby dies during late pregnancy. Intrapartum death, which is more common, occurs when a baby dies while the mother is giving birth.

The cause of stillbirth is often unknown, but the rate of babies who are stillborn is higher in twins and multiple births. Caesareans or inductions are advised after 38 weeks of pregnancy for twins, because the risk of stillbirth increases after this time. For otherwise healthy twin pregnancies where both twins are head down a trial of vaginal delivery is recommended at between 37 and 38 weeks.

Twin studies are utilized in an attempt to determine how much of a particular trait is attributable to either genetics or environmental influence. These studies compare monozygotic and dizygotic twins for medical , genetic , or psychological characteristics to try to isolate genetic influence from epigenetic and 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 used widely in the exploration of human nature. Classical twin studies are now being supplemented with molecular genetic studies which identify individual genes. Among dizygotic twins, in rare cases, the eggs are fertilized 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. This phenomenon is known as heteropaternal superfecundation. One study estimates that the frequency of heteropaternal superfecundation among dizygotic twins, whose parents were involved in paternity suits, was approximately 2.

Dizygotic twins from biracial couples can sometimes be mixed twins , which exhibit differing ethnic and racial features. One such pairing was born in London in to a white mother and Caribbean father.

Heterotopic pregnancy is an exceedingly rare type of dizygotic twinning in which one twin implants in the uterus as normal and the other remains in the fallopian tube as an ectopic pregnancy. Ectopic pregnancies must be resolved because they can be life-threatening to the mother. However, in most cases, the intrauterine pregnancy can be salvaged. Among monozygotic twins, in extremely rare cases, twins have been born with different sexes one male, one female.

The probability of this is so small that multiples having different sexes is universally accepted as a sound basis for in utero clinical determination that the multiples are not monozygotic. Another abnormality that can result in monozygotic twins of different sexes is if the egg is fertilized by a male sperm but during cell division only the X chromosome is duplicated.

This results in one normal male XY and one female with Turner syndrome 45,X. Monozygotic twins can develop differently, due to their genes being differently activated. As of only two cases have been reported. Both ova are then fertilized, each by a different sperm, and the coalesced zygotes undergo further cell duplications developing as a chimeric blastomere. If this blastomere then undergoes a twinning event, two embryos will be formed, with different paternal genetic information and identical maternal genetic information.

This results in a set of twins with identical gene sequence from the mother's side, but different sequences from the father's side. Cells in each fetus carry chromosomes from either sperm, resulting in chimeras. This form had been speculated until only recently being recorded in Western medicine.

In , a study reported a case of a pair of living twins, which shared an identical set of maternal chromosomes, while each having a distinct set of paternal chromosomes, albeit from the same man, and thus they most likely share half of their father's genetic makeup.

The twins were both found to be chimeras. One was an intersex XX, and one a XY male. However, due to environmental factors, they can sometimes change their appearance and only look somewhat alike.

Meanwhile, fraternal twins, just like other siblings, are different. While identical twins come from the division of a single cell, fraternal twins come from different cells. Here are their characteristics:. Although some identical twins can be of different gender, most of them are of the same gender. Dizygotic twins stem from the fertilization of two different eggs by two different sperm. Also, they can be of the same gender or of different genders.

The odds of conceiving identical twins is the same worldwide: they occur in three out of every thousand births. However, the odds of having fraternal twins varies due to several factors, including the home country. For example, in Japan, six of every thousand births can be fraternal, while in India the odds are 15 in every thousand births.

This possibility is boosted in pregnancies through in vitro fertilization IVF. Is it risky to have identical and fraternal twins? However, the gestation period is successful in most cases. In addition, the gestation period is usually 38 weeks instead of 40 weeks. Therefore, you should go see your doctor for regular checkups and follow their instructions carefully.

In conclusion, several characteristics help distinguish between identical and fraternal twins. By analyzing the factors described here, you can easily establish your case. Things you should avoid while…. There is a close link between medical staff and patients in childbirth care. The relationship before, during, and after childbirth is strengthened when we know the rights and obligations of each party.

Constipation during pregnancy is a common ailment that affects many women. Postpartum anxiety and depression are conditions that often overwhelm many women around the world.

Twin - Wikipedia

Identical twins are also known as monozygotic twins. They result from the fertilization of a single egg that splits in two. Identical twins share all of their genes and are always of the same sex.

In contrast, fraternal, or dizygotic, twins result from the fertilization of two separate eggs during the same pregnancy. They share half of their genes, just like any other siblings. Fraternal twins can be of the same or different sexes. Identical twins are also called monozygotic twins. They result from the fertilization of a single egg with a single sperm. And as those cells divide and multiply, at some point very early in embryonic growth they split into two individuals.

So that you can imagine that the genetic material in these two identical twins is identical to each other, hence the name. The contrast to this would be fraternal twins, which are twins born at the same time. However, they are actually the result of fertilization of two different eggs, and thus can be different genders and look different, and have different characteristics.

What's becoming increasingly clear is even though we call identical twins identical, and we think of their genetic material as being identical, we need to be reminded that there are environmental influences that may change, actually, the characteristics of identical twins, reminding us, as we already know, that even though identical twins come from the same genetic material, in characteristics they may actually have differences as well.

Donna Krasnewich, M.

Zygote development between identical twins