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  #1601  
Old 07-18-2018, 07:11 AM
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Default Re: A Question For The Lone Ranger

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(Generally, a salt in which sodium is the electron donor looks, behaves, and even tastes very similar to a salt with the same electron receiver but potassium as the electron donor.)
I haven't looked close enough to say it's a 1:1 ratio, but a lot of the "low sodium" products use potassium as the replacement for that salty flavor.
Truth, and I use potassium salt in the house. People have noticed the difference.
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  #1602  
Old 09-25-2018, 09:24 AM
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Default Re: A Question For The Lone Ranger

Genetic macular degeneration. I hope I make sense, I'm a wee tired and trying to get this out while I'm thinking of it.

Old man I know, his mother had macular degeneration, and it turns out he picked up the gene too. According to him it's only passed down through women. Now how I understand genes handed down is:

If recessive disorder, woman would need two mutated X chromosomes, and thus 100% chance of passing on an affected chromosome to male or female offspring, and males would have the disorder (In most cases.) Females might pick up the disorder only if father has an affected X chromosome. Otherwise she would be carrying the gene.

If dominant disorder, woman would only need to have one affected X chromosome, could possibly have two but not necessary, and so 50-50 chance of any offspring picking up the gene.

In either case, a son who picks up the gene would not transfer it to his son, as he donates the Y chromosome, but would transfer 100% of the time the affected gene to a daughter.

So:
-Am I recalling high school biology correctly?
-Are there some edge cases out there where such a disorder would not transfer, ever, through the male?
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  #1603  
Old 09-26-2018, 06:38 AM
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Default Re: A Question For The Lone Ranger

There are actually quite a few mutations that can lead to macular degeneration, so it can be an autosomal disorder (in which case, it's inherited the same in males and females) or a sex-linked disorder.

The genetics of such things are a bit more complex than we're generally taught in school, because there are multiple forms of dominance, and it's not always true that a "dominant" allele completely masks the effects of a "recessive" allele. Still, for simplicity's sake, let's assume that this is indeed the case.


So yes, if the trait in question is sex-linked, that means the gene in question is located on the "X" chromosome but not the "Y" chromosome. Since a woman has 2 "X" chromosomes and a man has only 1, such traits will be inherited differently in males and females.


[The distinction between "genes" and "alleles" is sometimes a bit confusing. The gene for a trait corresponds to the region of a particular chromosome that codes for that trait. For example, we might talk about a gene for eye color. Alleles are variants of a gene -- so we might talk about an allele for blue eyes vs. an allele for brown eyes; those would be allelic variants of the eye color gene.]



Anyway, if the trait in question is sex-linked and caused by a recessive allele, the only way a woman could have the condition is if she inherited a recessive allele from each of her parents. (This would mean that her father definitely had the condition, and her mother was at least a carrier.)



If a woman has the condition, then each of her sons is essentially guaranteed to inherit an allele for that trait from her, since each of them inherits his single "X" chromosome from her. And since a son doesn't have a second "X" chromosome that might carry a dominant allele, he will have the condition.

Similarly, each of that woman's daughters will inherit a single recessive allele from their mother, and so will be a carrier at the very least. Whether or not a daughter has the condition depends upon what she inherits from her father. If the father doesn't have the condition, then each of his daughters will receive a dominant, normal allele from him, and so will be a carrier, but won't have the condition. If the father does have the condition, then each of his daughters will receive a second recessive allele from him, and so will have the condition.


So in other words, if the condition is the result of a sex-linked recessive allele, then a woman can only have the condition if she inherits the defective allele from both parents. If she inherits the defective allele from one parent but a functional allele from the other, she will be a carrier but won't have the condition.

If a woman is a carrier and her husband does not have the condition, there's a 50% chance each of their sons will inherit their mother's defective allele and so have the condition. There's no way (barring mutation) a daughter of this couple could have the condition (because each daughter will inherit a dominant allele from her father), but there's a 50% chance that each daughter will inherit a recessive allele from her mother and so be a carrier.

Thus, sex-linked recessive conditions are much more common in males. Given that a male inherits his single "X" chromosome from his mother, if that chromosome happens to carry a recessive allele, there's no way that the man's father could contribute a dominant allele for that trait that would mask the recessive allele's effects.




If a trait is caused by a sex-linked dominant allele, then the situation is basically reversed. In this case, a female has two opportunities to inherit the allele in question, whereas a male has only one.

A man who carries a dominant sex-linked allele will give it to each of his daughters -- and to none of his sons. A woman who carries one copy of the dominant allele has a 50% chance to give it to each of her children -- whether they're male or female.

So yes, sex-linked dominant conditions are more common in females than in males. (Deleterious conditions caused by dominant alleles are rare, however. This is because natural selection can easily weed dominant alleles out of a population, if they have harmful effects. It's much harder to rid a population of harmful alleles if those alleles are recessive.)



Under normal circumstance, since a father does not give his son an "X" chromosome, there is no way that a son can inherit a sex-linked trait from his father. Normally. It is rare, but a translocational mutation can transfer a gene from the "Y" chromosome to the "X", or vice versa. So it is possible (though extremely rare) that a father could pass an allele that is normally sex-linked to his son.
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  #1604  
Old 09-26-2018, 08:25 AM
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Default Re: A Question For The Lone Ranger

I get from that that in a purely binary system I had the basic idea down.

I had to squint and reread a few times though and that just tells me if I presented the old man with that post his head would unscrew and fall off. :) Otherwise what they're all doing is probably the right thing. Communicating with their doctors.

+1 :thanks:
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  #1605  
Old 09-26-2018, 09:23 AM
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Default Re: A Question For The Lone Ranger

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and that just tells me if I presented the old man with that post his head would unscrew and fall off. :)
If this old man has the genes for a head that can unscrew and be removed, I would have thought that would be a much more interest topic of discussion ...
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  #1606  
Old 09-26-2018, 09:32 AM
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Default Re: A Question For The Lone Ranger

Now, a related question for TLR: what actually is a gene?

I'm aware of there being 4 bases C, A, T, G in DNA, and that they pair up. I'm aware (and I think this is universal?) that 3 bases code an amino acid, and that although 3 bases with 4 possibilities for each gives 43=64 possible sequences, we (life on Earth) only have 20 or so amino acids (what happens with other sequences?). And then I think that sequences of amino acids code proteins.

Then what? Are genes these DNA codes for proteins? How does the cellular machinery know where a gene starts and stops? How do we? And least important of all, who comes up with the names for genes, like hox, engrailed (don't know where I remember that from)?
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  #1607  
Old 09-26-2018, 03:22 PM
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Default Re: A Question For The Lone Ranger

Hoo boy, that's something that'll take a bit of time ... after all, "What are genes and how do they work?" is a question to which entire textbooks are devoted -- big, thick, densely-written texts that weigh more than a small child.

I'll try to knock together a decent outline, but it may be a couple of days before I can get to it.
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  #1608  
Old 09-26-2018, 03:52 PM
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Default Re: A Question For The Lone Ranger

Huh? Aren't they just denim and shrink up in the dryer so sometimes it's like trying to put on Spandex. Those genes?

Or, more like Gene Kelly?
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  #1609  
Old 09-26-2018, 04:07 PM
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Default Re: A Question For The Lone Ranger

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Hoo boy, that's something that'll take a bit of time ... after all, "What are genes and how do they work?" is a question to which entire textbooks are devoted --
I started reading the Wikipedia article and :headasplode: I'm glad it's not just me!
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  #1610  
Old 09-26-2018, 05:44 PM
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Default Re: A Question For The Lone Ranger

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I'm aware of there being 4 bases C, A, T, G in DNA, and that they pair up. I'm aware (and I think this is universal?) that 3 bases code an amino acid, and that although 3 bases with 4 possibilities for each gives 43=64 possible sequences, we (life on Earth) only have 20 or so amino acids (what happens with other sequences?).

At least that one's simple. There is usually more than one sequence, up to six, that code for a certain amino acid.
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  #1611  
Old 09-28-2018, 06:04 AM
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Default Re: A Question For The Lone Ranger

Heard on NPR a discussion about DNA searches. One thing particularly caught my attention. The subject of being related to people of historical interest came up. The guest said that after a few generations, you "no longer share DNA with that ancestor". I had no idea.
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Old 09-28-2018, 06:45 AM
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Default Re: A Question For The Lone Ranger

Well, you have to share DNA with your ancestors. The DNA came from somewhere.

It's just that when you go back far enough, you're not guaranteed to share it with any particular ancestor, and even if you do, it might not be very much.

So if you go back 8 generations, you have 256 ancestors (absent inbreeding). Well, on average you'd have 1/256 of your DNA be from each one.

But that's on average. It will vary from that, in a few ways:

1. Mutations can obviously cause things not to match the ancestor's DNA
2. If you're a male, the Y-chromosome would be mostly from the patrilineal ancestor
3. Your mitochondrial DNA comes from your matrilineal ancestor, although it's not a very large amount of DNA comparitively
4. DNA is mostly inherited as whole chromosomes, and there are 46 of those.
5. Crossover (which can also happen to a small portion of the Y-chromosome) will recombine some of those chromosomes, so you can have a chromosome which contains portions from more than one of those 128 ancestors

But still, there are 256 ancestors but only 46 chromosomes... And even accounting for crossover, you likely have some ancestors that you have little or even no DNA from, and some that you have significantly more than 1/256th from. At some point (I don't know when) if you go back far enough you probably don't share any DNA with that person (with exceptions for direct patrilineal* and matrilineal ancestors).

*Probably only if you are yourself a male
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  #1613  
Old 09-28-2018, 03:31 PM
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Default Re: A Question For The Lone Ranger

I wonder how independent those 256 ancestors really are though. Is 8 generations still few enough to neglect 'inbreeding'? (Hardly seems the right word to use, given all breeding would be inbreeding by this definition!)
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  #1614  
Old 09-28-2018, 05:25 PM
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Default Re: A Question For The Lone Ranger

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Heard on NPR a discussion about DNA searches. One thing particularly caught my attention. The subject of being related to people of historical interest came up. The guest said that after a few generations, you "no longer share DNA with that ancestor". I had no idea.

Hairsplitting is necessary here, for one thing we share more than 99% of our DNA to begin with. What the guest meant would have to be qualified as sharing "at least one large, mostly unchanged chunk on the order of a chromosome's worth of DNA".
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  #1615  
Old 09-28-2018, 08:52 PM
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Default Re: A Question For The Lone Ranger

Yes, But made my point but with actual facts about shared DNA, not speculation!
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  #1616  
Old 09-29-2018, 02:09 AM
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Default Re: A Question For The Lone Ranger

There's endless opportunity for speculation here. Let's say most people spend all their lives in a village or the next, how likely is it that one of your ancestors lost a chromosome but then picks it up again from someone else? There are interesting combinatorial problems lurking there that one could put on a math exam.
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  #1617  
Old 09-30-2018, 02:06 AM
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Default Re: A Question For The Lone Ranger

LTR, I believe that some mushrooms are brightly colored so that you know they are toxic, but what about animals that are 'color blind', are there other clues that would tell them to not eat certain mushrooms? or do they just not eat mushrooms at all? I understand that most birds do not have a sense of smell and that some animals are 'color blind'.
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