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» Scarleteen Boards: 2000 - 2014 (Archive) » SCARLETEEN CENTRAL » Pregnancy and Parenting » biology teacher

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Author Topic: biology teacher
Member # 26390

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In my biology class, the teacher said a couple of things that I wanted to check up on. One was credible. He said that the possibility of having twins is moreso determined by the father's side of the family than the mothers. So, in my case, my maternal grandmother was an identical twin, but since she's on my mother's side, I'm not very likely to have them myself. Is that so?

The other was less credible to me. He said that a woman can have her period during pregnancy, so basically, you can get pregnant again while you're already pregnant. Result: fraternal twins, one being premature. He said he knew a pair of twins in this situation. How is this possible?

Posts: 410 | From: Dallas, TX | Registered: Dec 2005  |  IP: Logged | Report this post to a Moderator
Member # 33438

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First, a biology primer.

Identical twins come from one fertilized egg. This egg splits early in pregnancy, creating two babies, with identical DNA. Identical twins are also referred to as monozygotic, meaning "from one egg"

Fraternal twins come from TWO fertilized eggs, meaning that technically, such twins are no more similar than other sibilings. So, for example, a woman ovulates, and releases two eggs, which two sperm happen to find. This is the reason that fraternal twins can be diffrent sexes. Fraternal twins are also referred to as dizygotic, meaning "from two eggs".

Now onto your heritability question. You can only claim that having twins (in your family) is heritable if those twins are fraternal. Why? Identical twins are considered a strange occurrance of nature, if you will. There is no "egg splitting" gene. On the other hand, hyperovulation, or releasing many eggs at one time is know to be heritable and run in families, and will cause fraternal twins.

But only on the male side of the family? No, not necessarily. Only a female has ovaries, and therfore, would be able to pass on said gene. If she has sons, those sons may carry the gene, but it will obviously not take effect in their bodies. Now, if those sons have daughters, their daughters may carry the gene, and produce fraternal twins some day. This explains why twins may "skip" a generation. Really, you could have this gene from either parent, depending on where the hyperovulation originated. Hypothetically, you can pass these genes onto your (future) daughters. (WHEW that was long, sorry!)

Can a woman have her period during pregnancy? No. There is that "ever famed" implantation bleeding, but that is usually not mistaken for a period. If anything, it is mild spotting that lasts for only a day or so. Regardless, a woman does not ovulate when she is already pregnant. It's physically impossible. Her body knows that it's carrying a baby-her hormones that would normally induce ovulation are focused elsewhere, and not performing the same tasks. Getting pregnant again while already pregnant is simply an urban legend.

Hope that answered some of your questions? Anyone have anything to add that I may have missed?

[ 06-16-2007, 11:58 PM: Message edited by: LittleMissSunshine ]

Posts: 64 | From: Minnesota | Registered: Apr 2007  |  IP: Logged | Report this post to a Moderator
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Oh I'm sorry Nailo. Per your chances of having twins...same as the rest of the population. Based on the above, identical twinning doesn't run in families.
Posts: 64 | From: Minnesota | Registered: Apr 2007  |  IP: Logged | Report this post to a Moderator
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(Awesome response, LittleMissSunshine! [Smile] Good to see users posting well-researched answers here!)


Posts: 2332 | From: Canada | Registered: Mar 2006  |  IP: Logged | Report this post to a Moderator

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