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Being a scientist and science nerd in general, I was surprised by the two different sperm fertilizing the same egg. Not to get too scientific, but in school, we were taught the zona pellucida helps protect the egg and is responsible for mediating the initial meeting of sperm and egg. Cortical granules filled with enzymes line the inside of the cell membrane, and help make sure that only one sperm can fertilize the egg.
As the sperm approach the egg, they bind to the zona pellucida in a process known as sperm binding. This triggers the acrosome reaction, in which the enzymes of the acrosome are freed. These enzymes then begin to digest the zona pellucida and allow the sperm to tunnel toward the egg’s plasma membrane. When the sperm cell finally reaches the egg cell, the plasma membranes of the two cells fuse together and the sperm releases its genetic material into the egg.
Fusion also triggers the cortical reaction. When the sperm and egg fuse it triggers a release of calcium ions, which cause the cortical granules inside the egg to fuse with the plasma membrane. As they fuse, these granules release their contents outside of the cell, toward the remains of the zona pellucida. The enzymes of the cortical granules further digest the zona pellucida, making it unable to bind more sperm, while other molecules found in the granules create a new protective layer around the fertilized egg.
By creating a new barrier and destroying the initial interface between sperm and egg, the cortical reaction prevents polyspermy, or the fertilization of a single egg by multiple sperm.
Because of everything I just mentioned, the only way I can think of for two different sperm to fertilize the same egg, would be if it was at the exact same time, because once that new barrier is formed after a single sperm fuses to the egg, no other sperm are able to get in. It's like a built in "safety mechanism". There's a cool video out there somewhere, showing the outer member of the egg changing with what they call the "zinc spark", it's really amazing!
What you have described is if everything goes according to plan. Aside from two different sperm fertilizing at the exact same time, I could imagine that other possibilities include anyone who produces an egg that may not follow these "instructions" for whatever reason, whether the result of a mutation and/or other abnormality. I agree with Dr. Minkin's statement: "Never say never..."
DNA from commercial companies is mostly for entertainment purposes. I think they might even state as much, because they know it's just a very small slice of the big picture. It's very concerning to me how many people take it as gospel and think it's some sort of replacement for old school research. Very, very, very dangerous.
Have to agree: I know too many people who have done the tests via commercial companies and results are so far off you one has to wonder. The same with doing DNA on dogs.
Have to agree: I know too many people who have done the tests via commercial companies and results are so far off you one has to wonder. The same with doing DNA on dogs.
i did a dna that was so off the chart, it was "what the hell?" so couple year later i did another with same company but different name, address, credit card, and it came back identical
All this reflects what top genetic genealogists have been saying for years: take the ethnicity results with a huge grain of salt. People with little or no experience with this tend to fall into two extremes: they take it literally (if the test says I'm 23.8% Scandinavian it must be true), or they think the whole thing is a "sham" and can't be trusted at any level. Customers who understand the limitations of these tests and know how to treat their results with a healthy dose of skepticism (which is required in traditional genealogy) will get more out of them. The lack of skepticism in traditional genealogy leads to people copying mistakes wholesale from other trees ad infinitum, believing them to be accurate when they are not. "I saw it in Ancestry so it must be true."
You are so right.
In my view DNA testing has been a guide and invaluable tool for genealogy helping to locate those brick wall ancestors, another clue to the whereabouts of those relations that have been difficult to get a line on.
For the most part American records are digitized through "USGen".
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