Paternity test identical twins

[fish]

Identical twins both mate with a female and produce a child. How could you determine who the father is?

Identical twins result from when the zygote splits, so both twins will have the exact same DNA unless there was a mutation to the germ cells?

[nautica]

hmmmmm??? Good question.

They would both have the same copy of both alleles, surely mutations is not what they are looking for.

What do you think Monique, I am leaning toward not being able to tell, but sure there is something.

Nautica

[Monique]

Hm.. I don't know any statistics on this. There have been major problems with murder cases where twins were involved. I once saw a interview on 20/20, where a twin admitted he voluntarily took the place of his brother.. after a while the free brother started to feel guilty and turned himself in. So who did it?

There might be some mutational differences between the twins, but I am not sure whether it is feasable to go and look for those by sequencing a long stretch of DNA for instance..

[chroot]

The twins (presumably) have identical DNA. There's no way you could tell.

- Warren

[Monique]

Mutations occur during cell division. If the zygote splits early on during development, the chances are higher that such mutations will also be incorporated in the germ cells of such an individual and thus passed on to the next generation.

I don't know though what the odds are: 1 mutation in how many bases in a cell division.. I'd be interested to find out.

[Monique]

I am véry sure there must be cases in the literature where one in a monozygotic twin had an accidental mutation in an important gene and thus developed a phenotype, while the other didn't.

[Monique]

Literature search [:D]:

'Identical' twins with discordant karyotypes.

Nieuwint A, Van Zalen-Sprock R, Hummel P, Pals G, Van Vugt J, Van Der Harten H, Heins Y, Madan K.

Department of Clinical Genetics, University Hospital Vrije Universiteit, Amsterdam, The Netherlands. a.nieuwint@azvu.nl

A chromosomal abnormality in one of the fetuses of a monozygotic twin pregnancy is a rare phenomenon. In the prenatal unit of our cytogenetics laboratory we have recently come across two such heterokaryotypic twin pregnancies. In both cases ultrasound abnormalities were detected in one fetus of each twin pair. Chromosomal analysis showed that one twin pregnancy was discordant for trisomy 21 and the other for 45,X. Ultrasonographic examination suggested a monochorionic twin pregnancy in each case and DNA studies confirmed that both sets of twins were monozygotic. Both pregnancies were terminated. Biopsies taken from different sites of the placentas showed chromosomal mosaicism in both cases. There was no clear correlation between the karyotype found close to the site of the umbilical cord insertion in the placenta and the karyotype of the fetus. Sampling of amniotic fluid from both sacs is recommended in diamniotic twin pregnancies if one (or both) of the fetuses has ultrasound abnormalities, even if the twins are apparently monochorionic.

De novo 14484 mitochondrial DNA mutation in monozygotic twins discordant for Leber's hereditary optic neuropathy.

Biousse V, Brown MD, Newman NJ, Allen JC, Rosenfeld J, Meola G, Wallace DC.

Department of Ophthalmology, Emory University School of Medicine, Atlanta, GA, USA.

Monozygotic twin brothers, clinically discordant for Leber's hereditary optic neuropathy (LHON), had a heteroplasmic point mutation at position 14484 in the mitochondrial DNA that was not detected in their mother. Moreover, the mutation occurred on the rare European haplogroup X, rather than the haplogroup J commonly associated with the 14484 mutation. These data indicate that the 14484 mutation in this family was a new mutation, indicating that it was the de novo occurrence of a common, primary LHON mutation.

Discordant sex in one of three monozygotic triplets.

Dallapiccola B, Stomeo C, Ferranti G, Di Lecce A, Purpura M.

A case is reported of monozygotic triplets, discordant for phenotypic sex, in which the female presented at birth with the features of Turner's syndrome. Chromosomal analyses showed homogeneous 46,XY karyotypes in the lymphocytes of the three sibs, while a 45,X non-mosaic chromosome constitution was detected in skin fibroblasts of the female triplet. It is suggested that mitotic non-disjunction or anaphase lag occurring early during embryonic development accounted for the occurrence of monosomy X in one cell line of the affected triplet. Previous observations of monozygotic twin pairs discordant for chromosome constitutions are reviewed.

[LURCH]

Chroot is right, unless there is some form of mutation after the zygot devides, a mutation that passes on through reproduction (a very rare event), it would be imposiible to determine paternity between two identicle twins.

This brings up another interesting question. If a woman mates with two identicle twins and conceives twins herself (a likely event, as multiple births have been linked to heredity), is there any way to determine if the new zygots are from one father or both? It would seem to me there isn't. Theoretically, it could even be possible for "identical" twins to result from heteropaternal superfecundation. The twins would be genetically identical, but not monozygotic, nor even from the same father. That would be a real long-shot, of course, but not ruled out by genetics. The odds of the two being genetically identical would be no less than if they had the same father.

[Monique]

Originally posted by LURCH
This brings up another interesting question. If a woman mates with two identicle twins and conceives twins herself (a likely event, as multiple births have been linked to heredity), is there any way to determine if the new zygots are from one father or both? It would seem to me there isn't. Is having monozygotic twins linked to heredity? I don't think so. Only if the twin is monozygotic can you tell it is one father, if it is dizygotic.. there is no way to tell.

Theoretically, it could even be possible for "identical" twins to result from heteropaternal superfecundation. Say that again??!?

The twins would be genetically identical, but not monozygotic, nor even from the same father. That won't be possible since only half of the genetic material is passed on to the following generation. You'd have to calculate the chance that two genetically egg cell encounter two genetically identical sperm cells.

[Moonbear]

Originally posted by LURCH

This brings up another interesting question. If a woman mates with two identicle twins and conceives twins herself (a likely event, as multiple births have been linked to heredity), is there any way to determine if the new zygots are from one father or both?

The hereditary part of having twins isn't for identical twins, but for fraternal twins, where a woman ovulates two eggs rather than one. That would be passed through the mother's side of the family, not the father's. There would be no way to determine if both twins were fathered by different twins.

It would seem to me there isn't. Theoretically, it could even be possible for "identical" twins to result from heteropaternal superfecundation. The twins would be genetically identical, but not monozygotic, nor even from the same father.

Fraternal twins from the same father are genetically distinct. Every sperm carries half of the father's genes, but there are a huge number of possible variations on how those get sorted out. So it's even less likely that two offspring from two identical twins would both get the same complement of genes from the fathers.

[LURCH]

Originally posted by Moonbear
So it's even less likely that two offspring from two identical twins would both get the same complement of genes from the fathers.

How is it less likely? I thought it would be exactly equal in probability; very unlikely, but possible.

[Monique]

As I said:

Originally posted by Monique
That won't be possible since only half of the genetic material is passed on to the following generation. You'd have to calculate the chance that two genetically identical egg cells encounter two genetically identical sperm cells.

[Moonbear]

Originally posted by LURCH
How is it less likely? I thought it would be exactly equal in probability; very unlikely, but possible.

It would be equally probably that EITHER twin would have a single sperm containing a particular complement of genes fertilize a single egg (1 chance in some really high number). The probability that BOTH twins would have sperm with the exact same complement of genes fertilize two separate eggs at the same time is lower.

[Monique]

You have to multiply to probabilty of egg x to get fertilized by sperm y by the probability of egg x to get fertilized by sperm y.

[lab rat]

I know there is no medical research that backs up the idea of identical twins "running" in families...but, it sure is strange how some families have an unually high number of identicals and others don't.

[Tsu]

So it IS possible for fraternal twins to have different fathers?

[Monique]

Ofcourse, why wouldn't a dizygotic twin be able to have a different father? Although.. I've once heard something that the sperm of a second male who fertilizes a woman somehow has reproductive advantage. Still doesn't rule out fertilization by both men.

[Tsu]

Originally posted by Monique
Ofcourse, why wouldn't a dizygotic twin be able to have a different father? Although.. I've once heard something that the sperm of a second male who fertilizes a woman somehow has reproductive advantage. Still doesn't rule out fertilization by both men.
This was a topic of conversation in my biology study group a gazillion years ago. Even after all these years, I never got an 'official' answer to this question! Also, in the ovulation of two eggs -- does this happen simultaneously or can several hours (or days!) pass between the release of each egg?

[LURCH]

Originally posted by Monique
Ofcourse, why wouldn't a dizygotic twin be able to have a different father? Although.. I've once heard something that the sperm of a second male who fertilizes a woman somehow has reproductive advantage. Still doesn't rule out fertilization by both men.

That's actually a pretty fascinating field of research. The advantage of the last male has alot to do with the shape of the human penis (a fact only recently discovered, I believe). But the amount of advantage is as much a matter of psychology as physiology. It has long been known that these two factors are perhaps more closely related in the reproductive system than anywhere else. If, for example, a husband believes that his wife may be cheating on him, the composition of his ejaculation can actually be changed by that idea. He will still produce sperm of the usual type we all know and love, the type designed to empregnate (call it "reproductive sperm"). But he will also produce "spermicidal sperm", which act to prevent empregnation by another male. These spermicidal sperm come in two basic kinds; an active and a passive kind.

Passive spermicidal spermatizoa swim a certain distance and then stop, looping their flagela into a form resembling a fishing hook. Millions of these become entangled by each other's tails, forming a berrier. The active veriant swim about bumping into others. If the other sperm they bump into does not match the chemical signature of the husband, they attack and kill it chemically, then continue on searching for more. These are the wto types I know of, there may be more.

It's real warfare in there!