Can you have a girl and boy identical twins
All pregnancies start when a sperm fertilises an egg. This forms twins. These twins are called fraternal twins, dizygotic twins meaning two zygotes or non-identical twins. The technical name for this is dichorionic. Fraternal twins can be the same or opposite sex and their genes are as different as any other brother and sister. Often, same-sex fraternal twins look different — for example, they might have different hair or eye colour.
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First semi-identical twins identified in pregnancy
Every parent of twins faces the question "Are your twins identical or fraternal? Many think that being identical twins refers to how twins look and not how they form. Take a look at the biology that determines the sex combinations that are possible with identical and fraternal twins.
The terms identical and fraternal don't describe what the twins look like, but actually how they form. Identical monozygotic twins are always of the same sex because they form from a single zygote fertilized egg that contains either male XY or female XX sex chromosomes.
Fraternal twins can be either two girls, two boys, or one of each. These are the possible sex combinations:. Identical twins come from a single fertilized egg that splits into two. Before it splits, it is either male or female. After it splits, there are either two males or two females.
Identical twins have the same genetic origin. No direct cause of monozygotic twinning has been determined; it is not hereditary. Monozygotic twins represent about one-third of all twins. The result is either two male twins, two female twins, or one male and one female. The genetic similarity between fraternal twins is the same as any two siblings about 50 percent if they have the same mother and father.
They may look alike, or not, just like any sisters and brothers. Fraternal twins are the most common form of twins, representing about two-thirds of all twins. Also, most twins and multiples that result from fertility enhancing treatments, such as drugs or procedures like in-vitro fertilization, are dizygotic rather than monozygotic. Every rule has exceptions, of course. In this case, they are extremely rare exceptions, and it's not likely that the average person would ever encounter twins in this situation.
Note that there have been a few reported cases of a genetic mutation in monozygotic male twins. For some reason, after the zygote splits, one twin loses a Y chromosome and develops as a female.
It's extremely rare; less than 10 cases have been confirmed. Given the odds, it's safe to assume that While identical twins come from the same fertilized egg and share the same DNA combination, there are more possibilities for fraternal twins. Besides being the offspring of two sperm and egg combinations, they may have different genetic donors. Here are the different combinations:. You are likely to have to answer the same questions about your twins repeatedly.
Armed with a few facts about twins, you'll be able just to grin and bear it or enlighten the curious about the biology of twins. Get diet and wellness tips to help your kids stay healthy and happy. More in Ages and Stages. Identical Twins. Fraternal Twins. The Exception to the Twin Sex Rule. Genetically Dissimilar. View All. Was this page helpful? Thanks for your feedback! Sign Up. What are your concerns? Article Sources. Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles.
Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Turner Syndrome. Mayo Clinic. Twins, Triplets, and Other Multiples. Office on Women's Health, U.
Department of Health and Human Services. Related Articles. The Different Classifications of Unusual Twins.
The Difference Between Identical and Fraternal Twins
It only required a glance at the ultrasound for the doctor to know that he was looking at identical twins. The positioning of two amniotic sacs attached to one placenta was the giveaway. It would be a couple of months before he could tell the mother whether to expect two boys or two girls. What seemed certain was that her babies would share a biological sex.
Back to Your pregnancy and baby guide. In recent years, fertility treatments and the fact women are having babies later has made multiple births more common. Identical twins are always the same sex, so if your twins are identical, you'll have 2 girls or 2 boys. Non-identical dizygotic twins happen when 2 separate eggs are fertilised and then implant into the woman's womb uterus. It's usually possible to find out if you're having twins through your dating ultrasound scan , which happens at around 11 to 14 weeks.
Washington State Twin Registry
Young Brisbane twins, a boy and a girl, have been identified as only the second set of semi-identical, or sesquizygotic, twins in the world -- and the first to be identified by doctors during pregnancy. However, an ultrasound at 14 weeks showed the twins were male and female, which is not possible for identical twins. Identical twins result when cells from a single egg fertilised by a single sperm divide into two, so identical twins are the same gender and share identical DNA. Fraternal twins occur when each twin develops from a separate egg and the egg is fertilised by its own sperm. Dr Gabbett said if one egg is fertilised by two sperm it results in three sets of chromosomes, one from the mother and two from the father. Sesquizygotic twins were first reported in the US in Those twins came to doctors' attention in infancy after one was identified with ambiguous genitalia. On investigation of mixed chromosomes, doctors found the boy and girl were identical on their mother's side but shared around half of their paternal DNA. Professor Fisk said an analysis of worldwide twin databases pointed to just how rare sesquizygotic twins are. While doctors may keep this in mind in apparently identical twins, its rarity means there is no case for routine genetic testing.
Do twins run in families?
March Twins of different genders are universally accepted as a sound basis for a clinical determination that boy and girl twins are not identical. However, in extremely rare cases, boy and girl twins can stem from the same fertilized egg. Twins, who stem from the same fertilized egg, are called monozygotic twins. A woman ovulates and releases one egg.
Because fraternal, or dizygotic, twins are 2 separate fertilized eggs, they usually develop 2 separate amniotic sacs, placentas, and supporting structures. Identical, or monozygotic, twins may or may not share the same amniotic sac, depending on how early the single fertilized egg divides into 2. If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA. A boy has XY chromosomes and a girl has XX chromosomes.
Can Identical Twins Be Male and Female?
Hannah Brown does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment. We all know a set of twins; perhaps even a set of identical twins. In Australia, twins account for about one in 80 births. A boy and a girl from Brisbane, aged four, have been identified as only the second set of semi-identical, or sesquizygotic twins, in the world. They are the first to have been observed in utero in the womb.
Can Identical Twins Be Different Sexes?
But, as explained here , identical twins do not always look exactly the same. Using that definition, the answer is yes! Humans have 23 pairs of chromosome. One of these pairs of chromosomes, called the sex chromosomes X and Y , determine the sex of the person. Very rarely, a glitch in copying sex chromosomes can occur, either during the formation of sperm or egg cells, or during the divisions of the zygote after it is formed. The result can be a MZ twin pair of opposite sexes.
Every parent of twins faces the question "Are your twins identical or fraternal? Many think that being identical twins refers to how twins look and not how they form. Take a look at the biology that determines the sex combinations that are possible with identical and fraternal twins. The terms identical and fraternal don't describe what the twins look like, but actually how they form.
Congratulations, It’s Twins. The Doctor Is Perplexed.
In This happens when the fertilised egg 'loses' one of the copies of the Y chromosome when it is dividing into two embryos in very early development. The resulting babies are then male XY and female XO. The normal genetic make-up of a girl is XX.
Twins are two offspring produced by the same pregnancy. 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. There is no known genetic link for identical twinning.
Back to Pregnancy. It depends on the type of twins. There's no evidence that identical twins run in families. However, non-identical twins can run in families.