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  • [MUSIC]

  • We can inherit a lot from our parents. Hair and eye color, height. But we can’t inherit

  • everything, because some biological traits are acquired during our lifetime. The only

  • way to transmit biological information between generations is in the letters of our DNA.

  • But what if it’s not that simple? What if our environment, and our experiences can be

  • passed on to our children and grandchildren? Inheritance is turning out to be much weirder

  • than we think.

  • [MUSIC]

  • Every cell in your body holds an incredible 6 feet (1.8 m) of DNA. The same 6 feet of DNA,

  • each holding identical genetic instructions. Yet when skin cells regenerate every day,

  • the new ones somehowknowto become skin cells, not bone, or muscle. Something

  • beyond just DNA influences their destiny.

  • This is what scientists call epigenetics, differences in traits that aren’t due to

  • changes in the DNA sequence.

  • When it’s wrapped up inside the cell, tiny chemical flags on the DNA or the proteins

  • it’s coiled around signal the cell to turn certain genes on or off, so they make just

  • the right machinery to do their job.

  • These chemical flags are rewritten every day as organisms adapt to new environments, but

  • scientists are seeing something strange: some of these changes can be passed on to the next

  • generation.

  • Mice fed high-fat dietsget fat (unsurprisingly) thanks to changes in the chemical flags on

  • their DNA. But female children of these obese mice, even though they were taken away and

  • raised by normal-sized mothers, still ended up 20% fatter than mice from skinny parents.

  • In another example, male mice trained to fear a fruity odor passed sensitivity to this smell

  • on to their children and grandchildren, even though their offspring had never been exposed

  • to it.

  • If this sounds a lot like what that guy Lamarck was talking about, well, youre not wrong.

  • Before Darwin, many scientists thought acquired traits could be passed on, but natural selection

  • proved that wrong.

  • But even so, scientists have since seen cases in species from flowers to fruit flies where

  • traits are passed on to children and grandchildren without changing the DNA sequence.

  • There’s just one catch. This shouldn’t be possible.

  • Just hours after an embryo is conceived, its chemical flags are erased, so all the cell

  • types in the new body can be built from a blank slate. And cells destined to become

  • sperm and eggs get erased a second time. At least that’s what scientists thought. For

  • epigenetic inheritance to work, some flags must sneak through without being reset.

  • This strange inheritance might even happen in humans. During the Dutch famine at the

  • end of WWII, children undernourished in the womb still carried epigenetic changes more

  • than 60 years later. And since these changes happen in the womb, they could have a huge

  • effect on our health as adults. In Överkalix, Sweden, boys who lived through

  • good harvests had sons and grandsons with higher rates of diabetes and heart disease,

  • while boys who lived through winter famines had healthier grandsons - they lived an average

  • of 32 years longer. Strangely, girls who lived through swings

  • of feast and famine had granddaughters with higher rates of heart disease.

  • That’s confusing. But human lives aren’t easily-controlled lab studies.

  • And that’s why some scientists doubt this new kind of inheritance.

  • Epigenetic changes can definitely happen between one or two generations, but for a trait to

  • have an effect on evolution, it has to endure for dozens of generations.

  • When a baby’s developing, the cells that will make a grandchild are already present,

  • and can be exposed to to the same environment as the grandmother. That’s not inheritance

  • as much as super-duper-early exposure. For epigenetic changes to be truly inherited,

  • they have to be rewritten in every generation, we’d have to see them in great-grandchildren

  • and beyond, and that’s just not clear yet.

  • Even so, the vast majority of traits that make us who we are are written in our DNA

  • and it’s tough to totally rule out genetic changes or other factors even in the cases

  • weve seen. That’s the problem with studying complex animals whose lives are the product

  • of thousands of genes in trillions of cells. There’s a lot going on here.

  • But since many of our diseases are linked to stress, diet, or environment, it wouldn’t

  • be totally surprising to find out our bodies are affected in ways we didn’t know about.

  • Epigenetics is a young science, and it’s reminding us we have a lot to learn about

  • what makes us who we are.

  • Stay curious.

  • Hey guys, so epignetics, pretty cool. And pretty weird. We just touched the tip of the

  • iceberg of this really interesting new field, and if you want to dig in deeper, there's

  • a ton of great links down in the description for you to check out. You know what else is

  • awesome? Physics! Crash Course Physics just launched last week, it's hosted by Dr. Shini

  • Somara, and like all of the Crash Courses, you're gonna love it. So head on over and

  • dig in. Stay curious!



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B2 中高級

遺傳真的都在我們的基因裡嗎? (Is Inheritance Really All In Our Genes?)

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    Amy.Lin 發佈於 2021 年 01 月 14 日