Can identical twins be female and male?

Question

This has really confused me. My sister says there can but my two friends at school says that identical twins can only be same-gendered. Is this true?

Randomness : My friend, a male, has a twin sister ;) If you ask me, they do NOT look alike >.<

Then fraternal twins can still be look-alikes?

Ignore the statement above. I got confused.

Answer 1

Twins can be female and male but identical twins must be identical thus the term.

Answer 2

Actually, your friends may be referring to a news report that I saw earlier this year. There are VERY rare cases where indeed, identical twins were male and female. It may actually happen more often, but nobody tests the DNA. What I recall is that one was intersexed (which develops after the split).

Identical twins - one egg splits. They can be identical or mirror or partially identical (as in the case of the celebrity Olson sisters).

Fraternal - different eggs but born at the same time. Yes, fraternal siblings can look alike, just like sisters or brothers of different ages can look alike.

Answer 3

No, identical twins are just that. Identical! They have to be of the same sex. They are coming from a single egg that has divided into 2 separate eggs. This means each of the eggs will contain identical information. Including which sex the babies will be. If a set of twins are born (1 girl and 1 boy) they are considered fraternal twins. That type of twin comes from 2 eggs and can be different sexes or even have different blood types.

Answer 4

Probably not. Most likely, they will not look the same. However, there is a VERY slim chance of ab1 and ab2 having the same DNA: The chance is approx. 1 in 70 trillion. And that's if you're lucky! More explanation below. First off, identical twins are a result of a zygote forming then splitting into two babies. Second off, it's only a predisposition to fraternal (non-identical) twins that's inherited, which is inherited through the maternal line (mother's side. Mother's mother's side. etc.). Thirdly, there's the dominance/recessive issue, and sex-linked genes, not to mention incomplete dominance to deal with. And independent assortment. Dominance/Recessive issue: Let's say that all four people are hetrozygous for the tongue-rolling gene. Rolling is dominant to non-rolling. That means: Rr x Rr and Rr x Rr Rr x Rr = RR, Rr, Rr, rr (One Rr is really rR but the dominant allele is written first due to convention) So ab1 could be a tongue-roller while ab2 is not. Sex linked genes: Females are XX, Males are XY (in other words, the father decides the sex of the baby - gender is a social construct) Sooo....say that both males are colourblind and that both females carry the colourblind allelle. The cross looks like this: XX' x X'Y and XX' x X'Y XX' = normal female X'Y = colourblind male X'X' = colourblind female X'Y = colourblind male And you can see here how the sex can affect what genes are expressed. Incomplete dominance issue (a heterozygous individual shows an intermediate phenotype): Let's say that height is controlled by a single gene (it's actually polygenic - controlled by mutiple genes- for simplicity's sake.) and that TT = tall, that Tt, Tt, = medium height (again, one Tt = tT but the domiant allelle is written first due to convention.) and tt = short. Soo...if all are medium height then: Tt x Tt and Tt x Tt Tt x Tt = TT (tall), Tt, Tt, (medium height), tt (short) And then there's codomiance (both allelles are expressed equally) which shows up in things like blood type. AO (A blood type individual who carries the recessive O blood type allele) X BO (B blood type individual who carries the recessive O allele.) AO X BO = AO (A blood type individual who carries the recessive O blood type allele), BO (B blood type individual who carries the recessive O allelle.), AB (AB blood type individual), OO (O blood type individual) The presence/absence of rhesus blood type protein is a dominance/recessive issue. A positive type individual could have a genotype of ++ or +-. By contrast, an A negative type individual MUST have the -- genotype. Another point: there's also the issues of chimeras and the fact that the older the parents get when they father the children, the more likely it is that the cells will make a 'mistake' copying themselves into gametes.

Answer 5

I have identical twin boys and they have to be the same sex....thus the word identical. Other twins, whatever the sex ,are fraternal twins and not identical. The woman's egg that splits in two , is the one responsible for identical twins. The fraternal (meaning coming from the father and two eggs and fertilized by two different sperm will make fraternal twins, which is the answer to your question.

Answer 6

Yes they can,As the editor of this website, one of the most common questions I receive via e-mail involves the possibility of opposite sex identical twins. Science has now proven that though opposite sex twins are possible, they are highly rare, and involve genetic abnormalities and birth defects in the female twin.

For many years, conventional medicine has postulated that opposite sex twins must be fraternal, or dizygotic—formed from two separate eggs and two separate sperm. In fact, when women under go a Level II ultrasound mid-way through a twin pregnancy, if opposite sex babies are detected, the pregnancy is automatically deemed a fraternal twin pregnancy.

However, there have been at least three documented cases of boy/girl identical twins worldwide. The chain of events that leads to boy/girl identical twins begins with the fertilization of one egg by one sperm. This fertilized egg then splits into what will become two separate babies, both male. During the dividing process, however, one of the babies loses half of his genetic code (the "Y" portion of the "XY" genetic code that makes the child male) and becomes a girl by default. However, most girls have two X genes (XX) and this girl only has one (X__), which means she will suffer from Turner's Syndrome. Turner's Syndrome occurs in about 1 in 2,000 births, and its presence doesn't automatically mean that the woman affected by the syndrome was a twin, as it occurs in singleton pregnancies as well. Girls with Turner's Syndrome experience ovarian failure 90% of the time, and also may show physical signs of the syndrome, such as thick skin around the neck or heart problems. For more information on Turner's Syndrome, see the link at the end of the article.

Answer 7

Of course they CANNOT. If they are twins and boy and girl then they are fraternal twins, not identical. Identical have exactly the same DNA and that would be impossible with a boy and a girl. Identical twins come from the same egg splitting into two. Fraternal twins come from 2 seperate eggs being fertilized.

Answer 8

Identical twins must be the same sex to be identical. They are identical because they have the same exact genes. The gene for sex is xx (for girls) and xy (for boys). So, as you can see, they are not identical. :-)

The other kind of twinning is called fraternal twins. They can be same sex, or different sex. Their genes are not exactly the same. Their genes are are as different as the other siblings in the family.

That said, just because twins are the same sex doesn't mean they are identical.

For identical twins, parents and doctors have indications that the babies are identical but the only way to know for sure is to get genetic testing. And in fact, this is what my husband and I did. We got our twins tested and they are in fact identical twins. They are now 6 months old.

Answer 9

No they can't. Identical twins are created when a single egg splits. Fraternal twins can be male and female.

Answer 10

Identical, or monozygotic, twins develop from a single egg/sperm combination that splits a few days after conception. Their DNA originates from a single source, thus their genetic makeup is the same and the characteristics that are determined by genetics will be similar. Monozygotic twins are always of the same gender, except in extremely rare cases of chromosomal defect.