OK - so I've been puzzling about inheritance of colours in Dexters.
It looks like black is dominant and red recessive - so you'd expect two reds to always have a red - but is that so? In an idle (really idle?) moment I'm sure I found an exception to this in the herd book.
And then how do Duns work?
In fact - when I went all the way through the herd book (sad or what?) it seemed that just about any colour combination could produce any of the three colours?
Any thoughts out there?
Colours
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Alison@Hatherland
- Posts: 16
- Joined: Thu Dec 16, 2004 6:18 pm
- Location: Tiverton, Devon
Hi Alison
I've just been doing some reading on this, though I'm still trying to get matters clear. I am sure others have a better understanding than me, but this is how I understand things at present:
Cattle have 60 chromosomes - a chromosome is a set of linked genes. Each gene consists of two alleles, one from the sire and one from the dam. There is one gene on chromosome 18 which provides the basic determination of colour in cattle, of black or red. There are actually three possible alleles for this gene that may be found in any combination, let's call them - E, e and E+. E is always dominant and leads to black, e is recessive and two of them lead to red, E+ is known as "wild red" in Dexters and two of them are currently thought also to lead to red (though details about the "wild red" in Dexters have yet to be confirmed in genetic research). This means, as you suggest, that a red sire and a red dam will always have red offspring.
Dun occurs as a result of gene interaction on chromosome 8 - this was just discovered in 2002, in research which confirmed its uniqueness in Dexters. Dun thus depends on what happens at ANOTHER gene to the red/black gene. The dun allele is recessive, so two of the dun alleles need to be present at the gene on chromosome 8 to have an effect.
However, and this is the key point, two dun alleles do NOT have an effect IF at the other gene on chromosome 18 there are two red alleles, such as e/e. If a Dexter is e/e (18) and d/d (8), it will be red.
From what I've read so far, I think the following is the reason for this.
The way I conceptualise it is that the e allele causes red colouring in cattle hair. It does this by producing a pigmentation called phaeomelanin. E causes eumelanin pigment to be made which then "overwhelms" the phaeomelanin, producing black - in a sense, the red pigmentation is still there (sometimes you can see a red tinge to a cattle beast's black coat when it fades a bit in the sun).
What the dun gene does, when there are two dun alleles, is to produce a "dilution" of eumelanin, the black pigment. That is how the dun shades appear. Black is biochemically altered to brown. But the chemical doesn't work on phaeomelanin, the red pigment.
Other colour chractaeristics, like skin colour, white spots, etc. are due to interactions with other genes - so it all becomes quite complicated, but geneticists have worked out a lot of it.
NOTE: This is just what I have come to understand so far from my reading, and it may be inaccurate in places, but it makes sense to me so far. I will be putting this information, with links to useful Internet sources, on my www.dex-info.net website soon.
Does this help?
John
I've just been doing some reading on this, though I'm still trying to get matters clear. I am sure others have a better understanding than me, but this is how I understand things at present:
Cattle have 60 chromosomes - a chromosome is a set of linked genes. Each gene consists of two alleles, one from the sire and one from the dam. There is one gene on chromosome 18 which provides the basic determination of colour in cattle, of black or red. There are actually three possible alleles for this gene that may be found in any combination, let's call them - E, e and E+. E is always dominant and leads to black, e is recessive and two of them lead to red, E+ is known as "wild red" in Dexters and two of them are currently thought also to lead to red (though details about the "wild red" in Dexters have yet to be confirmed in genetic research). This means, as you suggest, that a red sire and a red dam will always have red offspring.
Dun occurs as a result of gene interaction on chromosome 8 - this was just discovered in 2002, in research which confirmed its uniqueness in Dexters. Dun thus depends on what happens at ANOTHER gene to the red/black gene. The dun allele is recessive, so two of the dun alleles need to be present at the gene on chromosome 8 to have an effect.
However, and this is the key point, two dun alleles do NOT have an effect IF at the other gene on chromosome 18 there are two red alleles, such as e/e. If a Dexter is e/e (18) and d/d (8), it will be red.
From what I've read so far, I think the following is the reason for this.
The way I conceptualise it is that the e allele causes red colouring in cattle hair. It does this by producing a pigmentation called phaeomelanin. E causes eumelanin pigment to be made which then "overwhelms" the phaeomelanin, producing black - in a sense, the red pigmentation is still there (sometimes you can see a red tinge to a cattle beast's black coat when it fades a bit in the sun).
What the dun gene does, when there are two dun alleles, is to produce a "dilution" of eumelanin, the black pigment. That is how the dun shades appear. Black is biochemically altered to brown. But the chemical doesn't work on phaeomelanin, the red pigment.
Other colour chractaeristics, like skin colour, white spots, etc. are due to interactions with other genes - so it all becomes quite complicated, but geneticists have worked out a lot of it.
NOTE: This is just what I have come to understand so far from my reading, and it may be inaccurate in places, but it makes sense to me so far. I will be putting this information, with links to useful Internet sources, on my www.dex-info.net website soon.
Does this help?
John
Hi Alison
Another way to respond to your questions is to note that it can be difficult to distinguish betwen red and dun sometimes when you are just looking at a Dexter. For a long time in the US, dun wasn't recognised and so dun Dexters were registered as red.
A Herd Book entry of red or dun is a result of a subjective decision on behalf of the breeder and very occasionally it might be wrong. Now that Dexter breeders understand the genetics much better, any such errors should be avoided more or can be tested genetically (in the US, it is strongly recommended that all non-black Dexters be DNA tested to confirm their colour).
Two red Dexters will always produce red. Two black Dexters can produce black or red or dun, depending on whether they each have two black alleles or not, and depending on whether they carry one each of the dun allele. I had better not continue until I do some calculations, as it becomes a little more complex when dun is involved.
John
Another way to respond to your questions is to note that it can be difficult to distinguish betwen red and dun sometimes when you are just looking at a Dexter. For a long time in the US, dun wasn't recognised and so dun Dexters were registered as red.
A Herd Book entry of red or dun is a result of a subjective decision on behalf of the breeder and very occasionally it might be wrong. Now that Dexter breeders understand the genetics much better, any such errors should be avoided more or can be tested genetically (in the US, it is strongly recommended that all non-black Dexters be DNA tested to confirm their colour).
Two red Dexters will always produce red. Two black Dexters can produce black or red or dun, depending on whether they each have two black alleles or not, and depending on whether they carry one each of the dun allele. I had better not continue until I do some calculations, as it becomes a little more complex when dun is involved.
John
So why are there different shades of Dun or Red? As in humans, where different people produce different amounts of melanin in their skin, does the amount of eumelanin or phaeomelanin produced by each individual animal, decide what shade of Red or Dun that particular animal is? Also, can one animal change shades, depending on the time of the year, ie. the amount of sunlight that animal is exposed to?
I don't really expect answers to all these questions. They're just interesting things to ponder, that's all. Genetics is an interesting subject.
I don't really expect answers to all these questions. They're just interesting things to ponder, that's all. Genetics is an interesting subject.
Inger
NZ
NZ
In reply to Inger,
If their coats behave the same as horses coats which seems quite likely they could have a slightly different coloured summer and winter coat. For instance the palomino I have now is very light in the winter and dark gold in the summer, whereas the bay is darker in the summer but lightens with the sun unless I rug or stable him.
Lightening with the sun is a known "problem" in the horse showing world, which is why people buy summer turnout rugs, often with neck covers as well so the coat stays a true colour and shines better. I did to this to my very unimpressed horses a couple of years ago when I wanted them to look good for the shows.
I don't know if serious cow showing people rug their cows but it wouldn't surprise me.
Stephanie
If their coats behave the same as horses coats which seems quite likely they could have a slightly different coloured summer and winter coat. For instance the palomino I have now is very light in the winter and dark gold in the summer, whereas the bay is darker in the summer but lightens with the sun unless I rug or stable him.
Lightening with the sun is a known "problem" in the horse showing world, which is why people buy summer turnout rugs, often with neck covers as well so the coat stays a true colour and shines better. I did to this to my very unimpressed horses a couple of years ago when I wanted them to look good for the shows.
I don't know if serious cow showing people rug their cows but it wouldn't surprise me.
Stephanie
Stephanie Powell
Duffryn Dexters 32824
Abergavenny
https://www.facebook.com/Duffryn-Dexter ... 609196773/
Duffryn Dexters 32824
Abergavenny
https://www.facebook.com/Duffryn-Dexter ... 609196773/
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Kathy Millar
- Posts: 725
- Joined: Wed May 19, 2004 4:53 pm
- Location: Vancouver Island, BC, Canada
Alison, you are not alone! I too read herd books although in my case it is a flock book. I will read it for hours even though I will never encounter most of the sheep and their genetics as I live on an island and there are very little Shetland sheep (or Dexters for that matter) here. I feel a bit more connected I guess when I read about what other folks are up to with their animals.
John, here is Canada we must now colour DNA any animals being registered as red. I too get very confused between some reds and some duns. Then again, you should try and sort out the colours of Shetland sheep!! :O
Kathy
John, here is Canada we must now colour DNA any animals being registered as red. I too get very confused between some reds and some duns. Then again, you should try and sort out the colours of Shetland sheep!! :O
Kathy
Kathy
Home Farm, Vancouver Island, Canada
Home Farm, Vancouver Island, Canada
Kathy
Thank heavens the Shetland Sheep Society here doesn't insist on registering lambs within 30 days like the Dexter people do. All those black lambs at birth gleefully changing colour over the summer to palest fawns and greys except those who stay black of course. Then there is the chart with 63 !! variations of markings to choose from all with practically unpronouncable names. And we have Dexter people fretting about which of the THREE colours applies to their cows. ???
Thank heavens the Shetland Sheep Society here doesn't insist on registering lambs within 30 days like the Dexter people do. All those black lambs at birth gleefully changing colour over the summer to palest fawns and greys except those who stay black of course. Then there is the chart with 63 !! variations of markings to choose from all with practically unpronouncable names. And we have Dexter people fretting about which of the THREE colours applies to their cows. ???
In NZ, working out whether the calf is Red or Dun, doesn't seem to be a big problem for breeders, that I have heard. When I had a Red calf with a black nose and was new to Dexters and their colour variations. I sent pictures to our Herd Registrar by email and He was able to decide for me. We registered the heifer as Black, because she had a black nose and sure enough, by six months of age, she'd turned Black. My guess is she carries Red. Which is why she started out Red with a black nose.
We have a grace time of 1 year in which to register the calf. So our system is easier to work with, than yours I think.
We have a grace time of 1 year in which to register the calf. So our system is easier to work with, than yours I think.
Inger
NZ
NZ