[Q] Black sheep

[paigetheoracle]

Is melanism in animals strictly genetic? Is there any evidence that it could be environmental? I ask because I've noticed in the way to work that there is a field where all the lambs are black (at least a dozen by my reckoning), yet other fields contain none or only a few, which set me wondering if what was eaten made any contribution?

[stereologist]

I've heard that black sheep were introduced into fields in a fixed ratio to the white sheep to make it easier to count the sheep in a field. No idea if this is correct, but it certainly suggests that the color of the sheep does not change.

[Moontanman]

Melanism by definition is totally genetic, I'm not sure if black sheep are considered classic melanism or not.

[Michaelangelica]

We did try to breed out black sheep. But some people- like amateur spinners and weavers- like multicoloured sheep and deliberately breed them. You may have been looking at a spinner's farm?

(Or a coalminer's episode of Shaun the Sheep?:hihi:)

 

Moths were said to change colour as pollution changed the colour of the trees and poles they settled on.

 

I would imagine natural selection and epigenetics could affect/effect an organisms colour

[paigetheoracle]

I've heard that black sheep were introduced into fields in a fixed ratio to the white sheep to make it easier to count the sheep in a field. No idea if this is correct, but it certainly suggests that the color of the sheep does not change.

 

Sounds a bit like an urban legend but it does 'kind of' make sense.

[enorbet2]

Why would melanism in any animal be different from that characteristic or any other in the human animal? IIRC since environment existed first, before DNA, that all inheritable characteristics are an adaptive response to environment, with the only exception being mutations, such as by chance radiation, toxins, etc which aren't necessarily adaptive but are still environmentally caused.

 

However in the case of fields of black sheep, unless one field has some extreme environmental difference usually unlikely when in close proximity, changes won't occur other than those already encoded along with the serendipity of the epigenome. In widely separated and different fields those changes incorporated into the genome will be very slow, taking place over many generations.

 

If I understand correctly, genetics, while interactive since Pandora's Box was opened, is primarily if not entirely reactive. Until and unless we discover some sort of DNA analogue for the birth of stars, environment seems to be the Prime Mover with Physical Law the pattern for any order out of chaos.

[stereologist]

Why would melanism in any animal be different from that characteristic or any other in the human animal? IIRC since environment existed first, before DNA, that all inheritable characteristics are an adaptive response to environment, with the only exception being mutations, such as by chance radiation, toxins, etc which aren't necessarily adaptive but are still environmentally caused.

 

However in the case of fields of black sheep, unless one field has some extreme environmental difference usually unlikely when in close proximity, changes won't occur other than those already encoded along with the serendipity of the epigenome. In widely separated and different fields those changes incorporated into the genome will be very slow, taking place over many generations.

 

If I understand correctly, genetics, while interactive since Pandora's Box was opened, is primarily if not entirely reactive. Until and unless we discover some sort of DNA analogue for the birth of stars, environment seems to be the Prime Mover with Physical Law the pattern for any order out of chaos.

 

Is this computer generated?

[Turtle]

:hyper: No one thought to Google the question??? :D No worries; it's what they pay me the big bucks for. :hihi:

 

Full article: >> Scientists Identify Genetic Basis For The Black Sheep Of The Family

...Classical genetics has associated alternative forms, or alleles, of the agouti signaling protein gene (ASIP) with coat color variation in a number of mammals including mice, rats, dogs, cats, pigs, and sheep. However, most research has been focused on the mouse, with little understood about the genetic basis for coat color in economically important livestock species such as sheep.

 

The wild-type coat color of sheep is typically dark-bodied with a pale belly, however sheep raisers have strongly selected for a uniformly white coat domestic sheep. A problem for the sheep industry is a recessive black "non-agouti" allele of the ASIP gene carried by white sheep that cannot be distinguished within the flock, resulting in black coat color at a low, but persistent frequency. Determining the exact genetic differences at the ASIP locus could assist in efficient selection for white coat color. ...

 

As to a field of all black sheep, one can only logically conclude they were selected to go there by humans and make no logical conclusions concerning their parentage. :hihi:

[Michaelangelica]

:hihi:

[modest]

As to a field of all black sheep, one can only logically conclude they were selected to go there by humans and make no logical conclusions concerning their parentage. :hihi:

 

:hyper: I agree. :hihi:

 

But, we could make logical conclusions about any future offspring. For a sheep to appear black it must have both recessive black alleles. If two black sheep knock hooves then, there should be a 100% chance that the offspring will also be black.

 

~modest

[Turtle]

:hyper:

 

 

I thought about putting that one up, but as the question is actually pretty good I decided not. :D

 

As to a field of all black sheep, one can only logically conclude they were selected to go there by humans and make no logical conclusions concerning their parentage.

 

I agree.

 

But, we could make logical conclusions about any future offspring. For a sheep to appear black it must have both recessive black alleles. If two black sheep knock hooves then, there should be a 100% chance that the offspring will also be black.

 

~modest

 

I know next to nothing about genetics, but I notice in the article they make no mention of the black sheep carrying the agouti alleles thingys, or passing them on. Moreover they make a couple comments that seem to imply that black sheep don't breed true. :hihi: Here's those bits & I'll let you herd me in the right direction on this one. :hihi:

 

Scientists Identify Genetic Basis For The Black Sheep Of The Family

...It was found that recessive black sheep harbor only poorly expressed non-duplicated agouti alleles, likely a result of a defective single-copy ancestral agouti gene promoter.

... and then...

For sheep raisers, this could ultimately mean a genetic test that would identify carriers of the black non-agouti allele. ...

[Michaelangelica]

What about black and white sheep?

or is that banned in USA?

I hope all hypography members are members of Shaun's fan club?

Shaun The Sheep - Meet the Flock

[modest]

I know next to nothing about genetics, but I notice in the article they make no mention of the black sheep carrying the agouti alleles thingys, or passing them on. Moreover they make a couple comments that seem to imply that black sheep don't breed true. Here's those bits & I'll let you herd me in the right direction on this one. :hihi:

 

Scientists Identify Genetic Basis For The Black Sheep Of The Family

...It was found that recessive black sheep harbor only poorly expressed non-duplicated agouti alleles, likely a result of a defective single-copy ancestral agouti gene promoter.

... and then...

For sheep raisers, this could ultimately mean a genetic test that would identify carriers of the black non-agouti allele. ...

 

I also know next to nothing about genetics :D

 

From what I recall of high school biology, each sheep will have two alleles either of which can be black or white. Since black is recessive the sheep must have two blacks for it to appear black. Since white is dominant it will appear white if it has even one white allele. If both parents are black then all four of the parent's alleles are black and there's essentially no copy of the white gene to pass on to the child sheep. The reverse would not be true of two white sheep parents because there could be a recessive black allele hiding. Without genetic testing there would be no way of knowing if the parents carry a single recessive black allele. If they both were a carrier (each parent had a single hidden black allele) then the offspring would have a 50% chance of inheriting the black version of the gene from each parent making a 25% chance of getting 2 blacks and appearing black.

 

That was my understanding and a couple web pages I found said the same:

 

RECESSIVE BLACK PIGMENTATION IN MERINO SHEEP - Fact Sheet

 

But, the site you linked seems to open up a different possibility that my knowledge of genetics is not sufficient to understand :hyper:

Scientists at the CSIRO Queensland Bioscience Precinct in Australia have now taken this step and identified the molecular mechanisms underlying white and black coat color in domestic sheep. The researchers investigated the genetic architecture of the ASIP gene in several sheep breeds by sequencing the ASIP locus and measuring gene expression. "Surprisingly what we found was in fact that the genetic cause of domestic white and black sheep involves a novel tandem duplication affecting the ovine agouti gene and two other neighboring genes, AHCY and ITCH," explains Dr. Belinda Norris, lead author of the study. "We discovered a novel mechanism in which the dominant white sheep is caused by the ubiquitous expression of a duplicated agouti coding sequence located immediately downstream of a duplicated ITCH gene promoter region." It was found that recessive black sheep harbor only poorly expressed non-duplicated agouti alleles, likely a result of a defective single-copy ancestral agouti gene promoter.

 

Scientists Identify Genetic Basis For The Black Sheep Of The Family

 

~modest :hihi:

 

EDIT: Here's a wiki description of the recessive / dominant allele thing:

 

Genetics - Wikipedia, the free encyclopedia

[Turtle]

just when ewe thought it was sheepish to not go black in the water, ya hear something new now through the grapevine. :( :) :hihi:

 

 

All-black penguin discovered | Yahoo! Green

 

...While multicolored birds will often show some variation, Dr. Baker explains that what makes this all-black King Penguin so rare is that the bird's melanin deposits have occurred where they are typically not present -- enough so that no light feathers even checker the bird's normally white chest.

 

 

Melanism is merely the dark pigmentation of skin, fur -- or in this case, feathers. The unique trait derives from increased melanin in the body. Genes may play a role, but so might other factors. While melanism is common in many different animal species (e.g., Washington D.C. is famous for its melanistic squirrels), the trait is extremely rare in penguins. All-black penguins are so rare there is practically no research on the subject -- biologists guess that perhaps one in every quarter million of penguins shows evidence of at least partial melanism, whereas the penguin we saw appears to be almost entirely (if not entirely) melanistic.