Curious Parents

When Sperm Meets Egg, Sparks Literally Fly

Light is sometimes used as a metaphor for life — you might "put someone's lights out" or tell them they're "the light of your life." But life and light aren't just linked poetically. When sperm meets an egg, there is a real flash of light. So in a way, life and light are one and the same.

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Baby, You're A Firework

Researchers at Northwestern University made this startling discovery in 2011, when they saw what they call "zinc sparks" at the point of conception in mice. In 2014, they figured out a way to capture images of the event taking place. And in 2017, they achieved the holy grail of biological research: the team observed the same thing occurring in human egg cells.

Egg cells rely on zinc for their most vital functions, from maturing into a healthy egg to developing into an embryo. The 2014 research showed that each human egg cell comprises around 8,000 zinc compartments, each of which contain a million zinc atoms. When sperm meets an egg — although, as the human experiments demonstrated, all you really need is a sperm enzyme — the egg releases a flurry of zinc atoms all at once. Under the researcher's fluorescent sensor, it looks like a microscopic fireworks show, studded with explosion after tiny explosion. The spectacle lasts for up to two hours after conception.

Good Egg, Bad Egg

This isn't just cool; it's incredibly useful. The size of these explosions tells scientists a lot about the viability of the embryo the egg will produce. For people going through the costly and emotional ordeal of in vitro fertilization (IVF), that's big news, since at the moment less than half of IVF treatments result in a live birth.

"There are no tools currently available that tell us if it's a good quality egg," said co-author Dr. Eve Feinberg. "Often we don't know whether the egg or embryo is truly viable until we see if a pregnancy ensues. That's the reason this is so transformative. If we have the ability up front to see what is a good egg and what's not, it will help us know which embryo to transfer, avoid a lot of heartache and achieve pregnancy much more quickly." If that doesn't light up your life, we don't know what will.

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Zinc Fireworks Reveal When Human Egg is Fertilized

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