SciFiber: How to Design a Sheep


In this next installment of SciFiber we will be exploring some of the genetic factors affecting the fleece color of sheep. This past quarter I was enrolled in a Biology class focusing on genetics and evolution and learned about epigenetics for the first time. Being the diligent fiber nerd that I am, I just had to know how to apply this new found knowledge to deepen my understanding of the science behind why the fiber we love works the way it does. Don't think that I have forgotten about my promise for a post on the makeup of keratinous fibers; it's in my blog queue and you'll be hearing from me again very soon!


We have all known a black sheep, and perhaps some of us have even identified as one. Black sheep of the family go against the grain, they embody traits seen in no other members. The phrase has permeated culture as the way to describe the oddball of the gene pool, but have you ever thought about where it came from?

 Well, yes, obviously. 

Well, yes, obviously. 

The literal black sheep of the herd is the singular black ovine in a sea of white (protip: just as cows are bovine and horses are equine, sheep are ovine). But why is the black sheep the odd man out? Why isn’t Axel here considered the white sheep of the family?

Knitters, this is where your intuition should be sparking. As Josh knows, you can’t overdye black. But you can dye white wool, and therefore white fleeces are far more desirable for dyers, knitters, and anyone who likes colorful clothing. So, in order to maximize profits, sheep farmers have been trying to reduce the number of black sheep in their flock for centuries. Every once in awhile a black sheep would pop out of a white/white pairing, but farmers are an intelligent breed, and were not surprised because they understood the role of heterozygotes in Mendelian inheritance (if that sounded like gibberish check out this primer, but don’t worry, you can save it for later, the rest of this post makes sense without it). But every few generations something different would come along.

The agouti sheep.

Also known as "badger face," sheep with agouti color patterns are rare and their fleece is desired by knitters, spinners and weavers who enjoy working with 100% natural, undyed wool. The richly colored fiber of agouti sheep has a natural variegation to it that spins up into drool-worthy handspun yarn. Angora rabbit breeders long ago recognized the beauty of agouti rabbits and began selecting for the trait during breeding. The result is a line of rabbits with incredibly beautiful, naturally variegated coats. This selection has taken hundreds of generations to stabilize, however, and you can bet your britches that an agouti sheep revolution won't happen overnight. In fact, the few breeders who have tried their hand at an agouti-based business have become frustrated by the inconsistency of the coloration of their sheep. From year to year and even from season to season sheep farmers have noticed drastic color changes in their agouti flock with seemingly little pattern1. If they were able to predict and control the color palatte of their flock we might see a boom of this beautiful wool. But what control can mere humans exert over ovine biological processes? The answer may lie in a developing subfield of genetics called epigenetics.

Before we unpack epigenetics

let's quickly go over the genetic factors affecting the coloration of sheep.


Genetics of Color in Sheep
Agouti-colored hair occurs in a wide range of mammals, most notably cats, mice, rabbits and, of course, sheep. Agouti hair is characterized by a banded structure of black and yellow pigments, and is a result of competition between two different signalling proteins at the Agouti Signalling Protein (ASIP) location in DNA. One of the signalling proteins creates pheomelanin, or yellow hair pigment, and the other creates eumelanin, or black hair pigment. Geneticists studying the ASIP location in both sheep and mice have found that the Agouti allele (or variation of the gene), is semi-recessive. That is, if you breed a white sheep and an agouti sheep you are most likely to produce a white offspring (agouti is recessive to white), but if you breed a black sheep and an agouti sheep you are most likely to get an agouti offspring (agouti is dominant to black).


 

Now, here’s where it gets interesting: researchers studying mice displaying agouti coloration have found that, through controlling the environment, they can affect whether mice display agouti or black coloration, and they've been able to hit just about every coloration in-between2. They have been able to exert this control using environmental factors that affect the epigenetics in these mice. Epigenetics describes a biological system of gene regulation where chemical reactions at the DNA level determine whether or not certain areas of the genetic code are turned "off" or "on." In the example below, all mice carry the agouti allele, however in the case of the black mouse it has been completely silenced (has been turned "off").

Just how have scientists been able to control the expression of agouti? One answer is through diet. Because the "offness" or "onness" of genes is related to the amount of methlyation at the gene location, increasing the amount of methyl in the diet of a pregnant mouse mom has shown to decrease the expression of the agouti allele in her offspring3,4. This means that, even in an agouti/agouti pairing, moms that eat diets rich in methyl can produce black babies. Even more interesting, there is some evidence that the amount of methylation, that is, the "onness" or the "offness" of the agouti gene, is heritable, meaning that it can be passed on to future generations of mice5.

So what does this mean for sheep?

 Maybe it's photoshop, maybe it's epigenetics!

Maybe it's photoshop, maybe it's epigenetics!

Unfortunately, while geneticists have been studying the DNA of mice for decades, interest in the genetic code of sheep has only recently surfaced. There is very little information about epigenetic effects in sheep coloring, but only because research has just begun! In just a few short years researchers have not only successfully located the ASIP gene in merino sheep but have also determined the role of the agouti gene in fleece color expression6. The gene duplication mechanism seen at the ASIP location in sheep is similar to that in the genome of mice, indicating that sheep farmers might soon be able to exert epigenetic control over their flock's fleeces through maternal diet alteration.

So keep your ear to the ground because I predict that within my lifetime we will have understood the epigenetics of sheep thoroughly enough that we might start seeing custom, boutique sheep colorations appearing on the market.










SciFiber: Welcome to the World of Fiber Science!

Yes, it's been a while, my friends. And I miss y'all every. single. day. If you've commented on my Instagram, Ravelry, Facebook and asked if I was planning on making a new episode... THANK YOU. If you haven't done any of those things but still found yourself here to read this post, THANK YOU TOO. I've missed my Hops and Hanks family and it's good to know that y'all have been missing me too.

The reality of my life right now is that I simply do not have the time to sit down and record a podcast episode, much less take the time to edit and produce it to the quality I prefer. The good news is that this is because I have so much on my plate at the moment and I'm loving all of it. I realize now that I started Hops and Hanks in an effort to escape from a "real life" that I was completely unhappy with. I intend to either write or speak more on this topic in the future, but just know that the support you all gave me during the first year of Hops and Hanks saved me. From a lot of things. I love you all.

The problem: even if I can't record episodes regularly, I want to make sure that this little internet home of mine doesn't die.

The solution: I'm going to write more. I can write in fits and spurts, as opposed to sitting down for the large chunks of time necessary to record podcast episodes. I can't promise any regularity, but this also means that whenever I update it's because there is something in my brain that I just have to get out. So you know it's gonna be good. 

One of the many, many things I've been working on in the months and months since I last updated this website is a little side research project on the structure of fiber. I gave a presentation last night to the Windy City Knitting Guild and I wasn't able to fit nearly enough information into the one hour time limit. So I thought I would try writing about it here, to give myself a little more space to ramble. What follows is the first post of hopefully many exploring the word of fiber science!


The world of fiber is a diverse one. While knitters like myself are at least familiar with using protein-based fibers like wool and silk, plant fibers like cotton and some synthetic fibers like acrylic, for the most part our understanding of the materials we are using usually stops there. I began researching the fibers I use in my knitting in an effort to better understand why they work the way that they do.

Why is wool so warm? How does it stay warm while it is wet? Why do alpaca sweaters grow irreversibly? Why does acrylic take dye so much better than wool? Just what, exactly, does it mean to make a yarn superwash?

These were some of the many questions bouncing around in my head when I was approached by the Windy City Knitting Guild to present on the topic of the science behind fiber, and I was more than happy to have an excuse to explore deeper the materials properties of the fiber we knitters use on a daily basis. I quickly found that there is a plethora of fiber research out there that has answered many of my questions, but it doesn't seem like most of it has been interpreted in a way for laypeople to understand. 

That's where I come in.

Because I am, very fortunately, a student at a research-oriented university, I have access to research journals and academic databases such as the Textile Research Journal. Which, the fact that this is even a journal that exists might be one of the most exciting revelations I have had during this little project. I mean, seriously?! An academic journal that has articles about the computational study of fabric drape? I mean, just look at some of these titles (with included interpretations!)...

 Interpretation: Which felts more, merino wool or alpaca?

Interpretation: Which felts more, merino wool or alpaca?

 Interpretation: How does the crimp of wool affect the way it feels against skin?

Interpretation: How does the crimp of wool affect the way it feels against skin?

And the list of really cool scientific articles does not stop there. So the point of this little blog series will be to pick out specific topics in bite-sized chunks for me to read about, hopefully understand, and then convey the most interesting bits to y'all, my Fearless Readers. Stay tuned for the first official exploration of fibers coming to a blog near you. And just for funsies, here's a sneak peak of what we'll be talking about...

SciFiber: Keratinous Fibers

What the heck is that weird s-shaped thing over there? Is that really a fiber? Why do I care? TUNE IN NEXT TIME.

 Thanks Dr. Desai [1]!

Thanks Dr. Desai [1]!


[1] http://drrajivdesaimd.com/?p=3458