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Is humanity losing DNA?


Asex

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Let's say half of Johnny's DNA is from his mother and half of his DNA is from his father.

There are many different halves that can arise from the complete DNA of his mother and so goes for the complete DNA of his father.

Let's say Johnny has a sister Jane that inherited from their mother exactly the half Johnny didn't and from their father exactly the half Johnny didn't.

So Johnny and Jane are a brother and a sister but genetically they are not related and could have healthy children.

In my opinion the odds for this happening are very small.

The reason I tell you about Johnny and Jane is because they are the only scenario in which humanity preserves the genetic material of the ancestors, all other scenarios lead to Johnny and Jane being genetically related which means some part of their parents' DNA was embodied twice while some wasn't embodied even once.

What do you think?

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Rising Sun

Each generation loses some DNA from their ancestors, but you don't take mutations into consideration. If there isn't too much inbreeding in a population, new mutations compensate what is lost. Without new mutations happening all the time, humankind would die from inbreeding depression sooner or later.

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If what you're asking is "Are humans losing genetic traits", then over time yes, previously existing traits vanish. However, new ones emerge from mutations.

Over time, humans are actually gaining DNA. There is a trend for species to have more chromosomes the longer they've been around. Ferns are amongst the oldest living things on the planet and have hundreds of chromosomes, whereas the relatively young human species has a meager 46 :P

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MoraDollie

DNA is never really "lost" to be frank. You have what's called genetic markers that basically tell the DNA when to turn specific traits "on" and when to turn it "off". When something is turned "on" or "off" has a LOT of factors that go into it (gene history, stress, enviornemental factors, etc).

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scarletlatitude

Let's say half of Johnny's DNA is from his mother and half of his DNA is from his father.

There are many different halves that can arise from the complete DNA of his mother and so goes for the complete DNA of his father.

Let's say Johnny has a sister Jane that inherited from their mother exactly the half Johnny didn't and from their father exactly the half Johnny didn't.

So Johnny and Jane are a brother and a sister but genetically they are not related and could have healthy children.

In my opinion the odds for this happening are very small.

The reason I tell you about Johnny and Jane is because they are the only scenario in which humanity preserves the genetic material of the ancestors, all other scenarios lead to Johnny and Jane being genetically related which means some part of their parents' DNA was embodied twice while some wasn't embodied even once.

What do you think?

*biology hat time*

DNA is not lost. (Law of conservation of matter) Humans have 46 chromosomes in 23 pairs. If you are missing some DNA, you are either never born or you have a genetic condition. That DNA that you are missing happened because your parents' gametes (egg and sperm) did not go through meiosis correctly. Some of the gametes ended up with more chromosomes and some ended up with less. Still, the total amount of DNA is conserved, just not split evenly.

What you mean is that human DNA is recombined. You are 1/2 mom, and 1/2 dad. The DNA doesn't disappear. It just gets rearranged into new combinations.

You most definitely are genetically related to your siblings. Yes you get 1/2 from each parent, and even if they got completely separate halves from mom/dad, they would still have older, ancestral DNA in common. They would still have grandmom/granddad DNA, great grandmom/granddad DNA, etc. It is impossible for them to NOT have some DNA in common... unless they are adopted siblings from completely different parents.

I don't understand what you mean by "embodied twice"? DNA is always mixed up. Unless you have an identical twin, you are supposed to have different DNA from your parents. That's the whole point of sexual reproduction. For organisms that reproduce asexually (ha!), they are genetically identical to their parents. This is not a good thing, because whatever can kill the parent can kill the offspring. Sexually reproducing organisms have gotten around that problem by mixing up the DNA. You are different from every other human for a reason -- hopefully, if evolution worked correctly, you should have the right combination of DNA to survive.

As was said above, there are a lot of environmental factors as well. There is a whole science called "epigenetics" which focuses on changes to DNA that do not come from the DNA molecule itself. The environment turns DNA on or off. There is a possibility that you have DNA, but it is just not turned "on" because you do not have the right set of epigenetic markers. That doesn't mean that the DNA ceases to exist, just like turning off a light switch doesn't make the light bulb vanish forever.

I think what you are referring to is evolution by natural selection. If so, then yes, genetic traits are supposed to appear and disappear over time, depending on what is favored in the environment. But, the DNA doesn't disappear. It is just changed. If you replaced your light bulbs with the new fancy CFL bulbs, it would still be a light that works just the same, but now it's a different kind of blub. Same idea with evolution. Same molecule, different arrangements.

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Rising Sun

Scarlet, I think Asex is talking about inbreeding and loss of genetic diversity here. Or if not, I didn't understand the question right.

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Skycaptain

Correct me if I'm wrong here, but don't siblings always carry enough shared DNA that a genetic fingerprint has a near 100 % accuracy in showing that a person is or is not related to another person.

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SorryNotSorry

DNA isn't all humanity is losing...

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Correct me if I'm wrong here, but don't siblings always carry enough shared DNA that a genetic fingerprint has a near 100 % accuracy in showing that a person is or is not related to another person.

I think a comparison of your DNA with your father's could show that you are NOT his child (same with your mother's), but I don't think you can make a bet regarding sibling DNA.

But I'm really scientifically ignorant, so I shouldn't say.

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LenaLuthor

DNA isn't all humanity is losing...

In some ways, humans are getting dumber. In other ways, humans are getting smarter.

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Correct me if I'm wrong here, but don't siblings always carry enough shared DNA that a genetic fingerprint has a near 100 % accuracy in showing that a person is or is not related to another person.

I think a comparison of your DNA with your father's could show that you are NOT his child (same with your mother's), but I don't think you can make a bet regarding sibling DNA.

But I'm really scientifically ignorant, so I shouldn't say.

AFAIK, it's certainly more of a gamble (i.e., you have no chance to reach the ~99% certainty that you can reach with parent-child comparisons/paternity tests), but you can still make what amounts to a reasonably educated guess when comparing sibling DNA, especially when you increase the number of genetic markers compared. (And if my math isn't off, it should be the same odds with grandparent and grandchild, too.) An average of 25% identical markers over the billions of theoretical combinations may not be proof beyond reasonable doubt anymore, but is still more than impressive enough that I'd advise it to be the direction to place your bet in.

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DNA isn't all humanity is losing...

In some ways, humans are getting dumber. In other ways, humans are getting smarter.

Yup. I don't think evolving from australopithecus to sapiens is getting dumber.

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TeddyMiller

Just considering one couple and their children, yes, some DNA isn't passed down. However, if you consider that couple as part of a large population, there are lots of other members of their generation who have some DNA in common with them, so pretty much all of the DNA in the older generation will also be in the younger generation.

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Just considering one couple and their children, yes, some DNA isn't passed down. However, if you consider that couple as part of a large population, there are lots of other members of their generation who have some DNA in common with them, so pretty much all of the DNA in the older generation will also be in the younger generation.

To ensure that *all* individual DNA gets passed down, every individual would need to have an infinite amount of kids. (Stochastics being what they are - every additional kid just gives another 50% chance for every gene that was missed out previously.)

Clearly, that isn't even a theoretical possibility, and the genepool is meant by natural necessity to have a bunch of genetic combos become lost forever, in every generation. No problem either, because - if the birth rate is high enough to approach or overcome mortality - it also constantly produces new combos, all the time. And the best thing? If it worked any differently than this constant loss and constant random replacement, then evolution would be utterly impossible, and intelligent design would be the best scientific explanation for the variety of species. So, no worries - individual DNA dying out is just as it has to be, unless you're a hard creationist, ;)

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As a matter of fact... we may have been keeping too much!

I remember reading a theory about how the developments in medicine and technology allow almost everybody to survive (and therefore pass their genes t the next generation), while in a modelic "survival of the fittest" scenario the least beneficial ADN sequences would be lost. While technically they could be right, I don't really agree. I think what we can offer to the world and the next generations go beyond basic survival - who's to say a "weak" but creative person is not what we need right now? ;)

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  • 3 weeks later...
scarletlatitude

Just considering one couple and their children, yes, some DNA isn't passed down. However, if you consider that couple as part of a large population, there are lots of other members of their generation who have some DNA in common with them, so pretty much all of the DNA in the older generation will also be in the younger generation.

To ensure that *all* individual DNA gets passed down, every individual would need to have an infinite amount of kids. (Stochastics being what they are - every additional kid just gives another 50% chance for every gene that was missed out previously.)

Clearly, that isn't even a theoretical possibility, and the genepool is meant by natural necessity to have a bunch of genetic combos become lost forever, in every generation. No problem either, because - if the birth rate is high enough to approach or overcome mortality - it also constantly produces new combos, all the time. And the best thing? If it worked any differently than this constant loss and constant random replacement, then evolution would be utterly impossible, and intelligent design would be the best scientific explanation for the variety of species. So, no worries - individual DNA dying out is just as it has to be, unless you're a hard creationist, ;)

It's the traits that are dying out. The DNA is being mutated. It doesn't really "go" anywhere. Although we are correct that it may or may not get passed onto offspring depending on what each sperm or egg get. Sorry to be a stickler for terminology.

Also you have to be careful about humans and natural selection. It doesn't apply to us in quite the same way because we can change our environment to suit our needs. Other species can't do that.

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Titus Oates

Yeah, if we didn't lose some genetic traits we would still be looking like tiny hairy cavemen, right? Some of those genes just aren't in the mix anymore.

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