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i-e3899186ef576991098fed4ff62eab0f-small_dice.gif‘Tis the holiday season and, according to ancient lore, the time when miraculous events are most likely to take place.

One of those well-known and miraculous events of ancient days was the birth of a son to a young girl, who, although she was married (Okay, I’m not sure about this part of the story) she was said to be a virgin and the birth to be a miracle.

Hmmm.

How do you think the news would be received if that sort of thing happened today?

Certainly, if the young girl were to produce a grilled cheese sandwich with a burn spot that vaguely resembled a woman in a robe, someone might be able to sell it on Ebay and all kinds of people would consider it some kind of miracle (for many different reasons). But if the girl produced a baby, let’s face it, most of us would question her ability to do this on her own without some kind of help. Some people might even consider using a bit of science to test her claim and find out if she was right.

Lizards do it

We do know, out there in wild, wild, kingdom of Omaha, that the virgins of some species can and do give birth. This phenomenon, called “parthenogenesis,” has been documented in frogs, sharks, birds, mice, Komodo dragons, and Daphnia (1, 2). Sometimes, this occurs naturally, and sometimes parthenogenesis occurs when biologists mess around with eggs and test tubes. Whatever the cause, parthenogenesis involves activating an egg so that it develops in the absense of sperm. By knowing what’s involved we can make some predictions that would help us test whether or not parthenogenesis has really happened (or not).


i-2fe719f5fa76260d57e240ee267c0a6b-komodo.jpg

Girls, girls, girls

The first prediction we can make about virgin birth concerns the sex of the offspring. Human females are female because we have two X chromosomes. If we had even a single Y chromosome, we’d be male. Since a virgin mother only has X chromsomes, she only has the genes to make girls.  So all children from a virgin birth, in humans, would have to be female (Uh oh!  Keep in mind, I’m writing about science, not supernatural happenings).

 

Going farther

Okay, so virgin females can only give birth to girls. Lots of women who give birth to girls are not virgins. What other tests could we use to figure out if a girl is telling the truth?

i-792336aa4e22289f904fac9d2a971b57-genotype.gif

 

We could use one of many different methods to look at the child’s genotype. If the child is female, and the mother was a virgin, then most if not all of the child’s DNA should be identical to DNA from the mother and every genotype that we examine in the child should be homozygous.

There are several methods that we can use to test this.  The essential point is that every site we examine in the child’s DNA should have two identical copies of the same sequence. Genotyping is a term that we use to describe looking at those similar positions. If we consider the DNA in our own chromosomes, sometimes we find that sequence is identical in both chromosomes and sometimes it’s different.

One way to examine genotypes is by looking directly at the DNA sequence. In this DNA trace graph, you can see that most of the molecules have the DNA sequence
i-c944e0871f512c5a140079c31e60ccd5-common_seq.png.

i-ad08db89411110c5bd8ee0b725420a84-short_trace.png

When we look at the next base though, at position 181, we see a green peak and a red peak on top of each other. This means that approximately half of the molecules had an “a” at position 181 and the other half had a “t.” (We see this same pattern at position 184, too). 

From these results, we can say that one chromosome has the genotype A and the other has the genotype T. Now, I don’t which genotype came from the mother and which one came from the dad, but I do know that there are two different genotypes in this DNA sample.

If these data came from a sample of human DNA, we’d simpy have to grit our teeth and say “sorry kid, you may be miraculous, but your birth was not..”

References:

1. Edwards RG. 2007 “The significance of parthenogenetic virgin mothers in bonnethead sharks and mice.” Reprod Biomed Online. Jul;15(1):12-5. Review.

2. Chapman DD, Shivji MS, Louis E, Sommer J, Fletcher H, Prodöhl PA. 2007. “Virgin birth in a hammerhead shark.” Biol Lett. 2007 Aug 22;3(4):425-7.

Comments

  1. #1 RM
    December 3, 2007

    I’m unsure of the mechanism of parthenogenesis, but I don’t think being homozygous is a requirement. Given that the mother is heterozygous, and if each allele is a random choice from the mother’s genes, some loci of the child will be heterozygous as well.

    Additionally, due to mutations, we also can’t rule out getting a physically male child from (natural) parthenogenesis. There is always a small chance that a hormone/sex development pathway will be mutated so as to cause an XX male to form. Exceedingly rare, but possible.

  2. #2 Sandra Porter
    December 3, 2007

    RM,

    I guess I should have added a bit more explanatory information in my post.

    Eggs are made through a process called meiosis. During this process, the number of chromosomes in each pre-egg cell gets cut in half. The egg that results only has a single copy of each chromosome.

    During parthenogenesis, that egg, with it’s single copy of each chromosome, gets stimulated somehow and the proteins inside that egg copy the egg’s DNA, creating two copies of each chromosome. As a result, the egg now has two identical copies of each chromosome. All the cells that arise from that egg will also have two identical copies of each chromosome, and thus every chromosome is homozygous.

    Now, as to the question of can we get a male child if we start with female chromosomes? I don’t see how that could happen. Human females are only female because our genomes lack a Y chromosome. Even with mutations, you’re not going to turn an X chromosome into a Y chromosome. And, if a child doesn’t have an X chromosome, it will die. Consequently, the offspring must all be female.

  3. #3 Gustavo
    December 3, 2007

    Since a virgin mother only has X chromsomes, she wouldn’t have the genes to make girls.

    You might want to correct that sentence. :)

    As for the mechanism for parthenogenesis, do we know for sure it involves meiosis at all? Testable hypothesis – are the parthenogenetically generated komodo dragon girls really fully inbred? At least in pythons, they appear not to be so.

  4. #4 Karl
    December 3, 2007

    Sorry, failure of logic.
    (I am not Christian, not religious, in fact atheist)
    You are arguing from a non-theist point of view. The Christian response would be: GOD can do anything he wants. The laws of genetics do not apply. So all you can do, if you could examine Jesus’ DNA, is prove parthenogenesis, you cannot disprove it. The other DNA would be GOD’S.

  5. #5 Ken Shabby
    December 3, 2007

    Marriage requires consummation. In the story, the mother wasn’t married at the time of conception, and was still unmarried at birth, making the baby a bastard.

  6. #6 Sandra Porter
    December 3, 2007

    Gustavo: thanks for catching that. The error is fixed. With X chromosomes, you can only make girls.

    Now, back to the Komodo dragon story, in the Nature paper last December, all the sites that were tested were homozygous. However, only 7 sites were tested in the paper, so you could argue that a more thorough examination is warranted.

    As to the question of meiosis, my literature scan shows that people have only been able to find parthenogenesis happening in mammals is when they’ve taken extraordinary in the lab to make it happen. These cases generally involve using an ooctye (egg cell) and adding extra DNA or stimulating it somehow to make it divide.

    I have to look at this paper a little further, but it looks like nematodes produce homozygous offspring.

  7. #7 Marian Skupski
    December 3, 2007

    The best known example of this in vertebrates is in the lizard genus Cnemidophorus, where multiple species are parthenogenetic.

    The daughters are all clones of the mothers in the research that has been done to date

  8. #8 Sandra Porter
    December 3, 2007

    Thanks Marian!

  9. #9 sjohnson
    December 4, 2007

    I have to agree with Karl. The concept of “virgin birth” only means that there was no sexual intercourse and her hymen was not broken. There are other ways to fertilize her egg known to science nowadays. Bible even mentions that Jesus was a “Son of God”, so there was a male parent. It does not have to be parthenogenesis. Let’s not unnecessarily complicate things.

  10. #10 RM
    December 4, 2007

    Thanks for the clarification on the mechanism of parthenogenesis.

    Although a Y chromosome (specifically the SRY gene on it) is usually the defining factor in human sex determination, the physical “symptoms” of maleness are actually determined by a complex hormone cascade. There is a condition called XX male syndrome (de la Chapelle syndrome) where a patient is physically male, despite having no Y chromosome. Most of those cases are due to the translocation of the SRY gene from the Y chromosome to another chromosome. (This, of course, would require male involvement.)

    There are, however, a small fraction of XX males who are SRY negative. I can’t find details on the biochemical processes which underlie SRY negative XX male syndrome, but I imagine that it probably involves some mis-regulation of the sex determining hormones. Given that we know homozygous (highly inbred) individuals are more sensitive to genetic defects, there is a possibility that a human female would carry one or more recessive mutations which would cause SRY negative XX male syndrome, if homozygous. Alternatively, there could be one or more dominant mutations induced in the germ line after the mother developed, but before the parthenogenic infant does. Granted, this would be exceedingly rare (especially coupled with the chance of parthenogenesis), and definitely not the first possibility one would jump to, but we can’t rule it out with a simple “Y = male” type analysis.

  11. #11 Sandra Porter
    December 4, 2007

    RM: I knew about SRY translocations but I didn’t know about the other SRY negative XX cases. Do you have a reference? That’s really interesting!

    To date, no one has ever documented parthenogenesis in mammals, except under laboratory conditions where people have taken extreme measure to try and make it happen.

    Since parthenogenesis in mammals must be a rare event, if it even occurs in nature, and SRY tranlocations are also very rare events, I thought it best to stick with the case that would be most likely to occur, if it were to occur at all.

  12. #12 Sandra Porter
    December 4, 2007

    S & Karl: I defined virgin birth as a birth without a male parent, which would be the same thing as parthenogenesis.

    S.: I didn’t know that a virgin birth could be defined in other ways. Are you suggesting that in vitro fertilization would result in virgin birth?

    Karl: You’re absolutely right that I’m using a non-theistic description. That’s how science works. You’re right, too. It never crossed my mind to imagine that a deity might have DNA. I wonder what that genome sequence would look like.

    thanks for the comments!

  13. #13 Chris' Wills
    December 5, 2007

    I knew about SRY translocations but I didn’t know about the other SRY negative XX cases. Do you have a reference? That’s really interesting!

    http://www.the-scientist.com/news/display/25087/ mentions the SRY negative XX male condition and some tests done on mice.

  14. #14 Taylor Burns
    October 6, 2010

    Congratulations Marian, when you said that the daughters are all clones of the mothers in the research done to date.
    You hit the nail on the head.
    A normal birth, that is male plus female germ cells, results in the offspring having a mix of DNA and chromosomes from both parents, right? and can be XX or XY.
    In parthenogenensis, just from the very meaning of the word, we have offspring that are ‘clones’ of the one parent. They are produced from one batch of DNA.
    So, if the clones are from the mother’s somatic cell, they will be female, genetic copies of the mother.
    However, if the cloned offspring, are cloned form a somatic cell of the father, and implanted in the female for gestation purposes, that is male DNA, XY, then the resulting clones would be male, as in the case of Jesus Christ, and would be genetic copies of their father.
    Now the only thing is that in the case of Jesus Christ, we know he was the son of God, and it was a virgin birth, but we don’t know if he was half God/half Mary DNA or all God DNA. He could have been either.
    But if he was a clone, it would be all from his Father.
    So his birth would be parthenogenesis, with two possible sources.

  15. #15 Eva
    August 21, 2011

    Sorry, I’m no scientist. But I am Catholic. Speaking for our understanding of the virgin birth (And I believe all Eastern Christians in this case), the idea of God’s DNA is totally preposterous!

    Christ is called the Son of God with regard to his Divinity (pre-existing his incarnation in Mary’s womb) and the son of Man with regard to his human nature/his biology. So the idea of God having DNA as if God is a material being would be like the heresy of heresies in our churches, I’d presume. Are people actually suggesting that God had sex with Mary??? It’s called incarnation because the idea is that God (a pure spirit) “took on human nature”- It wasn’t his to begin with!

    Mary was Christ’s biological mother. How God provided for what a biological father would normally provide for, he has not told us. Perhaps he used this process you’re describing, parthenogenesis, perhaps he just provided for the male chromosomes (a type of miraculous invitro, if you will)- He is lord over nature after all. But there’s certainly no such thing as God’s DNA- What a ridiculous thought!

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