No I won’t ask you if is it swinging anyway if they swing… :dubious:
We know identical twins are basicaly clones of each other. But their children, technicaly cousins - is there posibility, that they are geneticaly identical (if both same sex). They do have set of parents with cumulative same genes.
If not, how apart would their DNA would be and why? And what if they had identical twins marrying another identical twin couple?
I knew “cousins” that we like this. They were opposite sex but they should really be considered genetic briother and sister. The chances of any two of them being identical are the same as any two siblings (not very likely).
They have the same change of being genetically identical as siblings do. (That is, such an infinitesimal chance as is effectively zero.) While the parents have the same genes, different spermatozoa and ova are each split in different ways, so have a different mix of genes.
It might help to imagine it this way.
Let the genes of two male twins be represented by 46 playing cards. These cards contain the 30 000 or so genes of the human genome. Each male twin has the same 46 cards.
Let the genes of the two female twins be represented by a different 46 cards.
When a male twin mates with a female twin, 23 cards are randomly selected by the male and combined with 23 cards randomly selected by the female. The two sets of 23 combine to give the full complement of 46 cards.
If you tried this at home with real cards, you would find that it would be virtually impossible to get the same result twice.
No, the two sets of twins could not produce identical children.
By the way, this explanation simplifies the idea of reproduction. In reality, nature makes it even more difficult to produce identical offspring in the situation you describe.
Well, not exactly. The 46 playing cards come in 23 pairs, and the 23 cards selected by the male (and female) must contain exactly one card from each pair. The gives you a lot fewer possible combinations than just randomly selecting 23 of 46, though it’s still a very large number.
Sure they could. But there’s only 1 chance in 2[sup]46[/sup] of it happening, same as with regular siblings.
You’re forgetting about the crossing over of homologous chromosomes that happens during meiosis. That shuffles the alleles even more, making it even more unlikely that you’ll get two identical individuals out of it.
This actually happened in my family. My paternal grandparents each had an identical twin, who married each other (in a double ceremony). My father and his siblings did look like their cousins, but nobody was anywhere close to “identical.”
Which raises a question: Are those of us in my generation (second cousins) actually first cousins, genetically? Would it be illegal for two of the second cousins to marry?
Genetically, yes. Legally, I would imagine not.
Kids of identical twin pairs would be genetically siblings.
Identical twins spring from a single cell.
Two women can’t share that single cell, so even if their children look similar, they can not be identical.
I imagine that would depend on whether the incest laws were written in terms of specific relationships or degrees of consanguinuity, and if they were written in terms of consanguinuity, whether identical twins are legally recognized as 100% consanguinuous.
Incidentally, many states alllow marriage between first cousins, but we can assume for purposes of your hypothetical that this is in a state which does not, or bump the question back up one generation.