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Author Topic:   How do you define the word Evolution?
New Cat's Eye
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Posts: 11816
From: near St. Louis
Joined: 01-27-2005
Member Rating: 1.6


Message 856 of 936 (813667)
06-29-2017 1:04 PM
Reply to: Message 855 by Faith
06-29-2017 12:51 PM


Re: Polyploidy -- evolution by doubling the genome
You shouldn't call yourself names...
This message is a reply to:
 Message 855 by Faith, posted 06-29-2017 12:51 PM Faith has not yet responded

  
Taq
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Posts: 7263
Joined: 03-06-2009
Member Rating: 3.7


Message 857 of 936 (813669)
06-29-2017 1:09 PM
Reply to: Message 853 by Faith
06-29-2017 12:50 PM


Re: Polyploidy -- evolution by doubling the genome
Faith writes:

Now we've got brown mice as well as black and white, and lots and lots of brown desert. That's a new version of the story.

There have been brown and black mice from the very start. Don't know where you got the white mice from.

The black mice are only found in limited areas that have black basalt rock outcroppings. In the vast majority of territory where pocket mice are found they are brown. The brown allele has not replaced the black allele, and the black allele has not replaced the brown allele. The black allele did not have to replace the brown allele in order for there to be black mice.


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 Message 853 by Faith, posted 06-29-2017 12:50 PM Faith has responded

Replies to this message:
 Message 858 by Faith, posted 06-29-2017 1:22 PM Taq has responded

  
Faith
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Posts: 26616
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 858 of 936 (813672)
06-29-2017 1:22 PM
Reply to: Message 857 by Taq
06-29-2017 1:09 PM


Re: Polyploidy -- evolution by doubling the genome
This is not the story that has been told about these mice before this. If there is no intense selection pressure then of course you're not going to lose the alleles for the other colors. That happens with intense selection pressure.
This message is a reply to:
 Message 857 by Taq, posted 06-29-2017 1:09 PM Taq has responded

Replies to this message:
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 Message 860 by caffeine, posted 06-29-2017 4:23 PM Faith has responded

    
Taq
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Posts: 7263
Joined: 03-06-2009
Member Rating: 3.7


Message 859 of 936 (813680)
06-29-2017 3:38 PM
Reply to: Message 858 by Faith
06-29-2017 1:22 PM


Re: Polyploidy -- evolution by doubling the genome
Faith writes:

If there is no intense selection pressure then of course you're not going to lose the alleles for the other colors. That happens with intense selection pressure.

But you said that the black allele had to completely replace the brown allele in order for that phenotype to exist. That isn't the case.


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caffeine
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(2)
Message 860 of 936 (813681)
06-29-2017 4:23 PM
Reply to: Message 858 by Faith
06-29-2017 1:22 PM


Re: Polyploidy -- evolution by doubling the genome
This is not the story that has been told about these mice before this. If there is no intense selection pressure then of course you're not going to lose the alleles for the other colors. That happens with intense selection pressure.

The story has not changed; you may just have misunderstood it before.

The animal is question is Chaetodipus intermedius. The image below is from Nature. Most Ch. intermedius are the same colour as the light brown in upper left and lower right.

A few, however, are darker colours like the other two in the image. These darker coloured ones live in parts of the Sonoran desert with dark black rocks from prehistoric volcanic eruptions. These dark areas are separated from one another. Dark and light mice freely interbreed.

The reason we only find dark mice in the areas with volcanic rocks is natural selection - this is your reduction of genetic diversity. Lighter coloured mice get eaten more often on the volcanic rocks; and darker coloured mice get eaten more often elsewhere. The reason the different alleles are not eliminated from the global population of Ch. intermedius is that the selection pressures are different in different places.

The reason Taq is so inordinately fond of these mice as an example of evolution, though, is that there is not one allele for dark colouration. Every isolated 'island' of volcanic rocks seems to have a different allele for producing black fur. Once this allele arises, natural selection maintains it in the area with the dark rocks; but prevents it from spreading to other places where it would be beneficial - since no mouse can carry the gene except across the sandy-brown desert.

This does not look like your preferred pattern of two ancestral mc1r alleles differentially expressed in different populations; with mutated forms that either do nothing or are detrimental. Instead, we see different mutated forms becoming dominant in different areas of black rocks where they're beneficial - whichever one happened to arise first.


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 Message 858 by Faith, posted 06-29-2017 1:22 PM Faith has responded

Replies to this message:
 Message 861 by Taq, posted 06-29-2017 5:46 PM caffeine has acknowledged this reply
 Message 862 by Faith, posted 06-29-2017 5:48 PM caffeine has not yet responded
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Taq
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Posts: 7263
Joined: 03-06-2009
Member Rating: 3.7


Message 861 of 936 (813683)
06-29-2017 5:46 PM
Reply to: Message 860 by caffeine
06-29-2017 4:23 PM


Re: Polyploidy -- evolution by doubling the genome
caffeine writes:

The reason Taq is so inordinately fond of these mice as an example of evolution, though, is that there is not one allele for dark colouration.

I would put that 3rd on the list of reasons I like this example. The 1st reason is that they were able to correlate the phenotypic change to mutations in a specific gene. The 2nd reason is that we know that this mutation could not have existed in ancestral pocket mice because the basalt outcroppings appeared in just the last few million years. Prior to these volcanic eruptions there were only brown mice because the black allele would have been selected against and removed from the population.


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Faith
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Posts: 26616
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 862 of 936 (813684)
06-29-2017 5:48 PM
Reply to: Message 860 by caffeine
06-29-2017 4:23 PM


Re: Polyploidy -- evolution by doubling the genome
In earlier discussions they were described as black and white or black and light.

In any case it is still true that to get one color means losing the other colors.


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 Message 860 by caffeine, posted 06-29-2017 4:23 PM caffeine has not yet responded

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Taq
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Posts: 7263
Joined: 03-06-2009
Member Rating: 3.7


Message 863 of 936 (813686)
06-29-2017 5:50 PM
Reply to: Message 862 by Faith
06-29-2017 5:48 PM


Re: Polyploidy -- evolution by doubling the genome
Faith writes:

In any case it is still true that to get one color means losing the other colors.

Getting a new color does not require the loss of the other color, as you have tried to claim.


This message is a reply to:
 Message 862 by Faith, posted 06-29-2017 5:48 PM Faith has responded

Replies to this message:
 Message 864 by Faith, posted 06-29-2017 5:56 PM Taq has responded

  
Faith
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Posts: 26616
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 864 of 936 (813688)
06-29-2017 5:56 PM
Reply to: Message 863 by Taq
06-29-2017 5:50 PM


Re: Polyploidy -- evolution by doubling the genome
In the population that must be black for the sake of survival it does mean either losing or severely reducing other colors.
This message is a reply to:
 Message 863 by Taq, posted 06-29-2017 5:50 PM Taq has responded

Replies to this message:
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Taq
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Posts: 7263
Joined: 03-06-2009
Member Rating: 3.7


(1)
Message 865 of 936 (813691)
06-29-2017 6:03 PM
Reply to: Message 864 by Faith
06-29-2017 5:56 PM


Re: Polyploidy -- evolution by doubling the genome
Faith writes:

In the population that must be black for the sake of survival it does mean either losing or severely reducing other colors.

But you don't need to eliminate the other color in order to have black mice, which is what you claimed before. It is the mutations that produce black fur, not the removal of the brown allele.


This message is a reply to:
 Message 864 by Faith, posted 06-29-2017 5:56 PM Faith has responded

Replies to this message:
 Message 866 by Faith, posted 06-29-2017 6:09 PM Taq has responded

  
Faith
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Posts: 26616
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 866 of 936 (813693)
06-29-2017 6:09 PM
Reply to: Message 865 by Taq
06-29-2017 6:03 PM


Re: Polyploidy -- evolution by doubling the genome
But you don't need to eliminate the other color in order to have black mice, which is what you claimed before. It is the mutations that produce black fur, not the removal of the brown allele.

But for the black fur to characterize the whole population in the black environment you have to get rid of the alleles for the other colors. I don't get why this isn't obvious. If they keep popping up they'll be eaten by predators until all that's left is the black mice. Why isn't this obvious?

Edited by Faith, : No reason given.


This message is a reply to:
 Message 865 by Taq, posted 06-29-2017 6:03 PM Taq has responded

Replies to this message:
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PaulK
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Posts: 13313
Joined: 01-10-2003
Member Rating: 2.0


Message 867 of 936 (813707)
06-30-2017 12:48 AM
Reply to: Message 866 by Faith
06-29-2017 6:09 PM


Re: Polyploidy -- evolution by doubling the genome
In reality it would take a long while to get rid of all the copies of the brown allele, because the black is dominant. Even if there isn't interbreeding with the brown population - and there probably is.

More importantly there can only be an overall decline in genetic diversity - even in a population of black mice - if there were multiple brown alleles. If there was only one allele at the start then ending up with one allele is not a decline.


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CRR
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Posts: 578
From: Australia
Joined: 10-19-2016


Message 868 of 936 (813714)
06-30-2017 4:27 AM
Reply to: Message 860 by caffeine
06-29-2017 4:23 PM


Re: Polyploidy -- evolution by doubling the genome
caffeine writes:

The reason Taq is so inordinately fond of these mice as an example of evolution, though, is that there is not one allele for dark colouration. Every isolated 'island' of volcanic rocks seems to have a different allele for producing black fur. Once this allele arises, natural selection maintains it in the area with the dark rocks; but prevents it from spreading to other places where it would be beneficial - since no mouse can carry the gene except across the sandy-brown desert.

This does not look like your preferred pattern of two ancestral mc1r alleles differentially expressed in different populations; with mutated forms that either do nothing or are detrimental. Instead, we see different mutated forms becoming dominant in different areas of black rocks where they're beneficial - whichever one happened to arise first.

You're right, this looks like the mcr1(brown) allele is the original and several different mutations can produce a dominant mcr1(black).

Coat colour is controlled in large part by the interaction of two proteins, the melanocortin-1-receptor (MC1R) and the agouti-signaling protein. The mutations in mcr1 prevent this interaction resulting in dark coats. So it's not that the mice have gained the ability to produce dark coats but rather they have lost control of the colour resulting in dark coats. So it is a loss of function mutation; one that is beneficial when the mice live on dark rocks.

Interestingly, another melanic population of these mice on a different lava flow shows no association with Mc1r mutations, indicating that adaptive dark color has evolved independently in this species through changes at different genes. http://www.pnas.org/content/100/9/5268.full


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 Message 860 by caffeine, posted 06-29-2017 4:23 PM caffeine has acknowledged this reply

Replies to this message:
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Taq
Member
Posts: 7263
Joined: 03-06-2009
Member Rating: 3.7


(2)
Message 869 of 936 (813742)
06-30-2017 11:53 AM
Reply to: Message 866 by Faith
06-29-2017 6:09 PM


Re: Polyploidy -- evolution by doubling the genome
Faith writes:

But for the black fur to characterize the whole population in the black environment . . .

That is not what we are talking about. You said that natural selection produces the black fur. This is false. It is mutations that produced the black fur, not selection.


This message is a reply to:
 Message 866 by Faith, posted 06-29-2017 6:09 PM Faith has responded

Replies to this message:
 Message 871 by Faith, posted 06-30-2017 11:59 AM Taq has responded

  
Taq
Member
Posts: 7263
Joined: 03-06-2009
Member Rating: 3.7


(2)
Message 870 of 936 (813743)
06-30-2017 11:56 AM
Reply to: Message 868 by CRR
06-30-2017 4:27 AM


Re: Polyploidy -- evolution by doubling the genome
CRR writes:

Coat colour is controlled in large part by the interaction of two proteins, the melanocortin-1-receptor (MC1R) and the agouti-signaling protein. The mutations in mcr1 prevent this interaction resulting in dark coats. So it's not that the mice have gained the ability to produce dark coats but rather they have lost control of the colour resulting in dark coats. So it is a loss of function mutation; one that is beneficial when the mice live on dark rocks.

Dark coat colors are a gain in function:

"In the laboratory mouse, loss-of-function mutations at Mc1r are recessive and result in light color, whereas gain-of-function alleles are dominant and result in dark color (16)."
http://www.pnas.org/content/100/9/5268.full


This message is a reply to:
 Message 868 by CRR, posted 06-30-2017 4:27 AM CRR has responded

Replies to this message:
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