Do twin always have the same blood type? And what if it is one of those cases where they're half-siblings?

Question

EDIT: Twins actually can be half-siblings. It's rarer in humans than it is in many other animals, but it does happen.

Answer 1

G'day yourpastlifelover,

Thank you for your question.

Human twins are two individuals who have shared the uterus during a single pregnancy and are usually, but not necessarily, born in close succession. A fetus alone in the womb is called a singleton. Due to the limited size of the mother's womb, multiple pregnancies are much less likely to carry to full term than singleton births, with twin pregnancies usually lasting around 34 to 36 weeks. Since premature births can have health consequences for the babies, twin births are often handled with special precautions.

There are five variations of twinning that occur commonly in the world. The three most common variations are all fraternal: (1) male-female twins are the most common result, at about 40% of all twins born; (2) female fraternal twins; (3) male fraternal twins. The last two are identical: (4) female identical twins and (5) (least common) male identical twins.

As so-called fraternal twins do not generally have the same genetic profile, the chances of them having different bloodtypes is reasonably high. Identical twins have the same genetic profile and therefore have the same blood type.

There is a chance of them being half-siblings but only if the mothers eggs were fertilised by the sperm of different men during the few days that she was ovulating. Such occurrences would be relatively infrequent. When it does occur, the genetic difference would be greater and therefore so would the chance of the siblings having different bloodtypes.

I have attached sources for your reference.

Regards

Answer 2

First of all explain half-sibling. Twins can't be half-siblings. Half-siblings are sisters and brothers who share one parent but not the other. The world you are looking for is "Fraternal twins" or "hetero-zygote twins" and that is when the one of the twins has developed from one zygot and the other one from another, like when one is a boy and the other one is a boy.
Second, in case of hetero-zygote twins, they can have different blood type. They are actually not very similar to each other. They are just as similar as any sisters and brothers.
In case of "homozygoye twins", those who have developed from one zygote, they share every thing: gender, blood type, eye color, hair color, .....

Answer 3

Actually you have a 12.5% chance of getting this blood type since you have a 50% chance of being B and a 25% chance of being - That means there is only a 1% chance of you both randomly getting this blood type... I think you are probably identical.

Answer 4

Twins need not have the same blood type, unless they are identical. Non-identical twins have different selections of genes. Half-siblings are not identical either, and can have different blood types.