If identical twins (a brother and a sister) had a child, would the child be identical to their parents? Would the son look exactly like his father, and the daughter like her mother?
... maybe there’s some odd condition I’m not familiar with, but at any rate since males have one X and one Y chromosome and females have two X and no Y chromosomes, I can’t figure how it’s possible for there to be genetically identical male and female persons.
There have been rare reports of male and female “identical twins” (see references below). Truly, none of the twins is genetically identical as they have a different complement of X/Y chromosomes. Their sex chromosomes differ, but their non-sex chromosomes are otherwise the same. I found no instances where both twins had the normal set of 23 chromosomes. Either one or both had genetic anomalies.
I tried looking this up before starting this thread, but I failed to find anything because I didn’t ask the right question; I guess I don’t have the Google gene in me.
I just thought it would be interessting having all the members of one family to look the same.
Even under those circumstances, I think all twins have the same chance of favouring one parent (looks wise) over the other. Not all boys favour their father. Sometimes they favour their mother and appear to be the masculine version of the mother. Same with girls and fathers too. I don’t think it’s too much different with twins.
Doug is correct that identical twins, barring the sort of extremely rare anomalies George mentioned, would have to be the same sex. However, it is an interesting question what might happen if the genomes of two such twins were combined. If this could be done in some way identical to sexual reproduction, except with both gametes coming from individuals of the same sex (which, as a picky aside, would really only be possible if they were female since the egg contributes a lot of needed stuff besides the genome, unlike the sperm), then I would expect the offspring not to be “clones” of the parents because of Recombination, a process in which the chromosomes of an individual line up in pairs and swap genes before dividng into different gametes. This would create new combinations of the same genes, thus leading to phenoptypic variation. Of course, since the variation between the two sets of chromosomes within one individual is small, the offspring would be a hell of a lot like the parents, more so than the offspring of two non-identical-twin parents.
On the other hand, if the process involved some sort of parthenogenesis, with a complete set of chromosomes from one individual providing all the gentic material without the recombination events of meiosis, then the offspring would be gentically identical to that individual, and naturally to its identical twin. Just another reason why life is more interesting because of sex!
Hmmm… twins.
I don’t wish to seem ungentlemanly, but how about if two identical twin brothers mated with two identical twin sisters?
I assume that recombination would play a similar role.
???
Not precisely sure what case you are suggesting.
If identical twins had kids with identical twins, their children wouldn’t be identical to each other; the DNA would be shuffled at each conception. Indeed, it would be no different from two individuals having two kids at different times ... parents have the same genetics, but the kids don’t.
If a set of Identical twin brothers married a set of identical twin sisters, the children then produced are scientifically (although not legally) considered siblings.
If a set of Identical twin brothers married a set of identical twin sisters, the children then produced are scientifically (although not legally) considered siblings.
Even under those circumstances, I think all twins have the same chance of favouring one parent (looks wise) over the other. Not all boys favour their father. Sometimes they favour their mother and appear to be the masculine version of the mother. Same with girls and fathers too. I don’t think it’s too much different with twins.
Just based on my own observations, I’ve come to the conclusion that boys often look like their mothers, while girls often look like their fathers. I’m always amazed by the uncanny resemblances. I always tell my sister how much my nephew looks like her, but she doesn’t see it. Once, a former co-worker showed me a headshot of herself as a newborn and one of her son as a newborn. The only difference between the two pictures was that one was in b&w;and the other in color. There were no physical differences whatsover, it was like looking at the same child!
What I also notice is that if, a girl looks like her father, she will probably resemble her paternal grandmother. Again, I’ve got no scientific evidence to prove this; it’s just a hypothesis.
I’ve never given any thought to how this works when the twins are male and female. I’ll have to pay even more attention now.
