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XYY possible?

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Postby weesper » Wed Aug 23, 2006 6:18 am

LilKim wrote:if 2 sperm fertilized one ovum you'd have a triploid fetus... with a sex chromosome complement that would could be XXY or XYY.


No, because triploid refers only to the full complement of an added haploid genome (ie 3n or 69 chromosomes); if you have one extra Y you're just aneuploid but not triploid. Note that a triploid state is actually euploid because it still has a normal ploidity.
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Postby LilKim » Wed Aug 23, 2006 6:47 am

weesper wrote:
LilKim wrote:if 2 sperm fertilized one ovum you'd have a triploid fetus... with a sex chromosome complement that would could be XXY or XYY.


No, because triploid refers only to the full complement of an added haploid genome (ie 3n or 69 chromosomes); if you have one extra Y you're just aneuploid but not triploid. Note that a triploid state is actually euploid because it still has a normal ploidity.


Again, I stand by what i've stated.... If 2 haploid sperm both bearing Y chromosomes fertilized a hapliod egg you would have: 23 chroms. (from sperm 1) + 23 chroms. (from sperm 2) + 23 chroms (from the egg) = 69 (... or 3N ...)

remember:
n = haploid (23)
2n = diploid (46)
3n = triploid (69)
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Postby MrMistery » Wed Aug 23, 2006 6:14 pm

i question wether or not this is physiologically possible in humans. True, humans have no slow block to polyspermy like organisms with external fertilisation, so sperms can "get in". But can they actually both fertilise the egg? Will the initial mitosis occur or will the zygote coduct apoptosis(or something similar)?
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Postby LilKim » Wed Aug 23, 2006 6:55 pm

I learned about the causes of triploid pregnancies in my baby-genetics course (maybe 5 years ago)...

Very few living- triploid fetuses are ever born ... because, most of them are aborted during pregnancy. However, I don't know that genetics based "follow-up" that can prove if it's the "2sperm + 1 egg" or "diploid egg + 1 sperm" or " an early endor reduplication event"

However, I do know that know that the actual phenotype of an aborted fetus and placenta depends on the number of chromosomes the fetus inherited from either parent. (they're called partial molar pregnancy) .

... I have some absolutely disgusting and disturbing pictures of these kinds of aborted fetuses (that I can share... if you'd like... but, they're gross!). However, if I remember correctly if the fetus inherits:

1.) 2N (from mom) + N( from dad)

the fetus is HUGE in comparison to the size of the placenta

2.) N (from mom) + 2N( from dad)

the placenta is HUGE in comparison to the size of the placenta


If you're interested... look up info for: Partial mole, partial molar pregnancy, hydatidiform mole.

interesting... yet, gross!
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Postby LilKim » Wed Aug 23, 2006 7:12 pm

I found this (_at_ http://www.marchofdimes.com/professionals/681_1189.asp)

"What is a molar pregnancy?

In a molar pregnancy, the early placenta develops into a mass of cysts (called a hydatidiform mole) that resemble a bunch of white grapes. The embryo either does not form at all or is malformed and cannot survive. About one in 1,000 pregnancies is molar. Women who are over age 40 or who have had two or more miscarriages are at increased risk of molar pregnancy.

There actually are two types of molar pregnancy, complete and partial. With a complete mole, there is no embryo and no normal placental tissue. With a partial mole, there may be some normal placenta and the embryo, which is abnormal, begins to develop.

Both types of molar pregnancy arise from an abnormal fertilized egg. In a complete mole, all of the fertilized egg’s chromosomes (tiny thread-like structures in cells that carry our genes) come from the father. Normally, half come from the father, and half from the mother. Shortly after fertilization, the chromosomes from the mother’s egg are lost or inactivated, and those from the father are duplicated. In most cases of partial mole, the mother’s 23 chromosomes remain, but there are two sets of chromosomes from the father (so the embryo has 69 chromosomes instead of the normal 46). One way this happens is fertilization of an egg by two sperm cells.

Molar pregnancy poses a threat to the pregnant woman when the mole penetrates deep into the uterine wall, which can result in heavy bleeding. Occasionally, a mole can turn into a choriocarcinoma, a rare pregnancy-related form of cancer."
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Postby Poison » Thu Aug 24, 2006 3:27 pm

MrMistery wrote:i question wether or not this is physiologically possible in humans. True, humans have no slow block to polyspermy like organisms with external fertilisation, so sperms can "get in". But can they actually both fertilise the egg? Will the initial mitosis occur or will the zygote coduct apoptosis(or something similar)?


A fertilized egg can fuse together with a sperm (one of the ways of chimerism formation). And the person has nothing different (except carrying different DNAs) from a normal individual. But I don't think this can be called 'fertilizing' as the egg is already fertilized.

LilKim wrote:... I have some absolutely disgusting and disturbing pictures of these kinds of aborted fetuses (that I can share... if you'd like... but, they're gross!).


If it doesn't look wierd to you, I think it is interesting.
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