How different can identical twins look

Dante Cadavez Pundit. Can twins have different dads? Superfecundation is the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse, which can lead to twin babies from two separate biological fathers.

The term superfecundation is derived from fecund, meaning the ability to produce offspring. Hinde Aldaz Pundit. Do identical twins have the same blood type? Identical twins will always have the same blood type because they were created from the same fertilized egg fraternal twins can have different blood types — again, providing the parents do — because they are created by two fertilized eggs.

Oliviu Cardeno Pundit. Can one twin have a disease and not the other? Identical twins provide an ideal setting to study this complex interaction. While they share the same genes, they sometimes differ in how these genes are expressed. And both members of an identical twin pair don't usually have the disease ; if one twin has it, the other will have it about 15 percent of the time.

Tanesha Iosif Teacher. Do identical twins have the same fingerprints? Identical twins do not have identical fingerprints , even though their identical genes give them very similar patterns.

Antonie Koppel Teacher. Do twins have the same retina? Yanis Vecino Teacher. Are identical twins the same height? Some identical twins can have different heights and weights. This is because height and weight are controlled by what you eat as well your DNA. This can mean one twin starts getting more to eat even before they are born!

Another physical difference between identical twins is their fingerprints. Natzaret Jockisch Teacher. Do identical twins both need glasses? Both wear glasses for severe farsightedness, one has been found to have astigmatism. Guasimara Lanero Reviewer. Can identical twins have different skin color? After all, while huge differences can and do happen with fraternal twins , identical twins are usually exactly that -- identical in skin , hair and eye color.

Ayyub Mombour Reviewer. What is it called when twins look alike? Identical Twins. Let us look at each scenario in detail. Scenario 1, both girls: The egg that always contains the X chromosome from the female is fertilized by a sperm containing the X chromosome from the male.

So the resulting zygote formed will have the XX chromosome, which develops into a baby girl. Now the egg splits in two and the both the resulting embryos will still contain the same genetic material and, therefore, the same sex. So both the babies will be females. Scenario 2, both boys: Similar to both females scenario above, if the egg containing the X chromosome from the female is fertilized by the sperm containing the Y chromosome from the male, the resulting zygote will contain the XY chromosome, which develops into a baby boy.

After the egg splits, the two embryos will have the XY chromosome and will both be males. Fraternal twins are dizygotic twins, where two eggs are released by the female which are fertilized by two different sperms from the male. The gender variations in such a case can be of three types which is represented in the table below. Scenario 1. Scenario 2. Scenario 3.

Egg 1. Scenario 1, both girls: The two eggs released by the female contain one X chromosome each. Now each of these eggs is fertilized by two different sperms. In this scenario, both the sperms contain X chromosome from the male. The two zygotes will each contain XX chromosomes and will develop into two baby girls. Scenario 2, both boys: The two eggs released by the female contain one X chromosome each.

In this scenario, both the sperms contain Y chromosome from the male. The two zygotes will each contain XY chromosomes and will develop into two baby boys. Scenario 3, one girl and one boy: The two eggs released by the female contain one X chromosome each. In this scenario, one of the eggs is fertilized by a sperm containing the X chromosome and the other egg is fertilized by a sperm containing the Y chromosome. So one of the zygotes will have the XX chromosome and will develop into a baby girl, and the other zygote will have the XY chromosome that will develop into a baby boy.

From this section we can easily see that identical twins always have the same gender, whereas fraternal twins can be of the same or different gender. But off course, there are always exceptions to the rule. Identical twins predominantly have the same sex.

But, there have been extremely rare instances where the monozygotic twins are of different sexes. This scenario is so rare that there have been only a few reported cases so far and it is unlikely that you will come across such twins in your lifetime.

Scenario 1: In this case, an egg containing the X chromosome is fertilized by a sperm containing the Y chromosome. The embryo thus formed will have the XY chromosome. Now the egg splits. Ideally the egg should split to result in two embryos, each having the XY chromosome.

But due to some inaccurate copying of the chromosomes, only one zygote has the XY chromosome and the other will not have the Y chromosome from the father and will result in XO chromosome. The embryo containing the XY chromosome will develop into a male, whereas the embryo containing the XO chromosome will develop into a female. This condition of having only one X chromosome is called Turner Syndrome and can result in short stature, lack of ovarian development, etc.

The male twin will be unaffected and will develop normally. Scenario 2: In the above scenario we saw a chromosome copying error that resulted in one sex chromosome being eliminated. But sometimes this copying error can also result in an extra sex chromosome to be added. An egg containing the X chromosome is fertilized by a sperm containing the Y chromosome.

The resulting zygote will have the XY chromosome. The embryo then splits to form two separate zygotes. One of the zygotes will have the same XY chromosome, but the other zygote will have an extra X chromosome due to the copying error resulting in a zygote containing the XXY chromosome. Further glitches result in the zygote eliminating the Y chromosome resulting in a zygote with XX chromosome. So the embryo containing the XY chromosome will develop into a boy and the embryo containing the XX chromosome will develop into a girl.

Scenario 3: There is a twin type called the polar body twins or half-identical twins. In this case the egg splits before fertilization and each egg is then fertilized by a different sperm. They don't act like either. One likes to dance; the other likes to play basketball. Certainly, we encourage them to pursue their individual interests, but the initial inclination towards these activities was all their own.

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 the chromosomal defect. On the other hand, fraternal, or dizygotic , multiples form when two separate eggs are fertilized by separate sperm in a single ovulation cycle.

While identical twins form with the same set of genes, human development is not just genetic. The environment also has an impact. So, beginning in the early environment of the womb, external influences can change the appearance of twins. For example, some monozygotic twins share a placenta. One twin may have a more advantageous connection to the placenta, receiving the first run of nutrients. This situation can cause a size discrepancy between the babies, a physical difference that continues as they grow up.

While most twins grow up in the same home environment, there are many circumstances that create differences in the children's appearances, personalities, and interests. As the twins approach the teen years, they may even seek to establish dissimilar qualities in order to establish individual identities.

Get diet and wellness tips to help your kids stay healthy and happy. Chatterjee A, Morison IM. Monozygotic twins: genes are not the destiny?. American Academy of Pediatrics. The Difference between Identical and Fraternal Twins. Updated November 21, American Pregnancy Association.