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I don't understand why an identical twin was needed to learn this. Couldn't an astronaut's DNA be sampled before and after a mission and compared?

88e282102ae2e5b 9y ago
Sure, but everyone is accumulating mutations all the time, so you need a control on the ground to see if space itself is affecting the mutation rate.
lithos 9y ago
Some accounting for a year of aging. Though the news press is probably more scientifically significant.
telchar 9y ago
Well, consider the counterfactual of what would have happened to the astronaut's DNA if he hadn't gone to space. We don't know how it would have changed, so we can't compare it directly. Since we needed to do the experiment I'm guessing our knowledge DNA was not sufficient to predict that, so it makes sense to use a twin to get the closest proxy to the counterfactual that we can.
mikhailt 9y ago
How would you rule out age-related changes since this specific astronaut was in space for a year? DNA is not fixed, they change all the time. It is always better to have more data points to rule out several variables, especially considering that it is rare to have an astronaut with a twin sibling.
- lostlogin 9y ago
  So how did it ever match his twin? Not being facetious but echoing the parent comments confusion. Do the age related changes occur the same way in identical twins?
  - mikhailt 9y ago
    This article may explain better than I can: https://arstechnica.com/science/2018/03/scott-kellys-medical-monitoring-has-spawned-some-horrific-press-coverage/ https://arstechnica.com/science/2018/03/scott-kellys-medical... > As a result, the more relevant comparison (and one NASA did) is Scott's DNA before and after his time in space. That can tell us how many changes were picked up while in space. But as noted above, he would have probably picked up some mutations even if he sat here on Earth. And that's where his twin Mark, who did sit here on Earth, comes in. Mark's before and after gives us a sense of the normal background rate of mutation on Earth. Comparing that rate to Scott's tells us the important number: the degree to which this rate is elevated in the environment of low-Earth orbit.
- everly 9y ago
  "DNA is not fixed, they change all the time." Then why is it significant that time in space changed it?
  - tytytytytytytyt 9y ago
    It might have changed it more or in different ways.
  - mikhailt 9y ago
    It’s the rate of change compared to his twin on earth. This ars article explains better: https://arstechnica.com/science/2018/03/scott-kellys-medical-monitoring-has-spawned-some-horrific-press-coverage/ https://arstechnica.com/science/2018/03/scott-kellys-medical...

88e282102ae2e5b 9y ago

Sure, but everyone is accumulating mutations all the time, so you need a control on the ground to see if space itself is affecting the mutation rate.

lithos 9y ago

Some accounting for a year of aging. Though the news press is probably more scientifically significant.

telchar 9y ago

Well, consider the counterfactual of what would have happened to the astronaut's DNA if he hadn't gone to space. We don't know how it would have changed, so we can't compare it directly. Since we needed to do the experiment I'm guessing our knowledge DNA was not sufficient to predict that, so it makes sense to use a twin to get the closest proxy to the counterfactual that we can.

mikhailt 9y ago

How would you rule out age-related changes since this specific astronaut was in space for a year? DNA is not fixed, they change all the time. It is always better to have more data points to rule out several variables, especially considering that it is rare to have an astronaut with a twin sibling.

lostlogin 9y ago
So how did it ever match his twin? Not being facetious but echoing the parent comments confusion. Do the age related changes occur the same way in identical twins?
- mikhailt 9y ago
  This article may explain better than I can: https://arstechnica.com/science/2018/03/scott-kellys-medical-monitoring-has-spawned-some-horrific-press-coverage/ https://arstechnica.com/science/2018/03/scott-kellys-medical... > As a result, the more relevant comparison (and one NASA did) is Scott's DNA before and after his time in space. That can tell us how many changes were picked up while in space. But as noted above, he would have probably picked up some mutations even if he sat here on Earth. And that's where his twin Mark, who did sit here on Earth, comes in. Mark's before and after gives us a sense of the normal background rate of mutation on Earth. Comparing that rate to Scott's tells us the important number: the degree to which this rate is elevated in the environment of low-Earth orbit.
everly 9y ago
"DNA is not fixed, they change all the time." Then why is it significant that time in space changed it?
- tytytytytytytyt 9y ago
  It might have changed it more or in different ways.
- mikhailt 9y ago
  It’s the rate of change compared to his twin on earth. This ars article explains better: https://arstechnica.com/science/2018/03/scott-kellys-medical-monitoring-has-spawned-some-horrific-press-coverage/ https://arstechnica.com/science/2018/03/scott-kellys-medical...