Forum: Author Hangout

I know a pair of twin girls, in real life, who are both blond-haired. Their grandfather, a close friend of mine, says at birth one had brown hair and the other had blond. Starting since middle school, they use hair-coloring to make their hair color the same.
My question: Are they identical twins? Does being an identical twin mean just that two siblings of the same gender were born at roughly the same time; or does it mean they have to look very much alike, including hair color? Or does it mean something else?

Does being an identical twin mean just that two siblings of the same gender were born at roughly the same time; or does it mean they have to look very much alike, including hair color? Or does it mean something else?

Identical twins have exactly the same DNA.

https://www.nhs.uk/pregnancy/finding-out/pregnant-with-twins/

Identical (monozygotic) twins happen when a single egg (zygote) is fertilised.

The egg then divides in 2, creating identical twins who share the same genes.

Identical twins are always the same sex, so if your twins are identical, you'll have 2 girls or 2 boys.

That said, not everything is 100% DNA controlled. some things are affected by developmental conditions.

Also, the reverse is also a possibility: Two fraternal twin embryos merge resulting in a single individual with two sets of DNA.

the test for Identical twins as stated before is coming from the same egg. what normally happens is the egg implants in the uterine wall and the cells start multiplying. then at an early stage of the doubling the zygotes split to two entities. if this split is late you can end up with Siamese or conjoined twins, but I digress. I was talking about the test. normally it is possible on ultrasound to determine if twins are identical then they will be attached to the same placenta and amniotic sac. so the parents may know reasonably early if they're expecting identical twins from an ultrasound. if however this is not the case the second test is during birth. a single placenta will be delivered after the babies. as for different hair colour this may come down to genome phenotype where the same DNA expresses differently due to environmental forces of expression. ie flipping a switch on one gene or a few. so yes it is possible for identical twins to have similar but different shades of hair. but you wouldn't for example get one blonde and one black. blonde and light brown 'may' be possible. ymmv.

I know a pair of twin sisters who are known to be fraternal, non-identical (certain fertility treatments have twins or sets as side effects). For us, the extended family, they are very different.

They have different natural body types, one is naturally willowy, the other needs to be careful to not become chubby. They have different face forms and structure. Different eye and natural hair color. Wastly different character.

Yet they are approximately the same height and through diet and excercise their current bodies are very similar. The differences in facial features aren't all that much anymore either, both being drop dead gorgeous.

That said, strangers have trouble to tell them apart, to the point that for a period when one had a driver's license and the other yet haven't, they shared mismatched document sets and got away with it, and some similar stunts normally reserved for identical twins.

I have known male identical twins and also female identical twins. Discussing this with a female twin years ago, she told me that:
- males have XY chromosomes, their physical characteristics are fixed.
- females have XX chromosomes, one of those is free to vary and this permits minor variations.

I have always assumed she was not simply making this up, and I could always tell the two of them apart at a glance. With the male pair I knew, the only difference I could see was that they dressed differently - consistently and deliberately.