Peafowl Genetics 205: Leucistic Mutations
What is Leucism?
So far we have learned about colors and patterns, which are pretty straightforward. But I haven't mentioned white, pied, silver pied, or white eye, and with good reason. While these may be considered "patterns" in a sense, what they actually are is something a little different than either of those things. They are leucistic mutations, or mutations that change the phenotype due to a genetic condition called leucism. Leucism causes the pigment cells in the bird's neural crest to fail to migrate to the right places during fetal development. This results in a white-diluted bird when it's pale leucism, patches of skin that contain no pigment cells (pied) when it's partial leucism, and a completely white bird when it's total leucism.
This is different than albinism! Albinism causes pigment cells to produce no melanin, but the pigment cells are still present, and can still produce other pigments, like reds and yellows.
What this means is that leucism doesn't alter any genes responsible for color or pattern. It does not dilute or saturate any given pigment, which is what color mutations are. And because it "deletes" the pigment cells altogether, no color or pattern can be expressed, even though the genes for those colors or patterns still exist in the bird. This makes white birds a bit of a challenge- "under" the white, the bird may have genes for any color (including all of the colors!) or pattern, but you would never know unless you bred the bird to a matching color or pattern. Some people describe this term as "masking" and that's probably a good way to look at it; that white/pied are not colors or patterns, but rather a mask over the bird's genetic color or pattern.
This is different than albinism! Albinism causes pigment cells to produce no melanin, but the pigment cells are still present, and can still produce other pigments, like reds and yellows.
What this means is that leucism doesn't alter any genes responsible for color or pattern. It does not dilute or saturate any given pigment, which is what color mutations are. And because it "deletes" the pigment cells altogether, no color or pattern can be expressed, even though the genes for those colors or patterns still exist in the bird. This makes white birds a bit of a challenge- "under" the white, the bird may have genes for any color (including all of the colors!) or pattern, but you would never know unless you bred the bird to a matching color or pattern. Some people describe this term as "masking" and that's probably a good way to look at it; that white/pied are not colors or patterns, but rather a mask over the bird's genetic color or pattern.
White-eye Notes
White-eye is a poorly-understood gene in general. For now, most people assume it is another leucistic gene, and that may be true. There is a third form of leucism, called pale leucism, which resembles what happens to silver pied birds, where the color is diluted with white and becomes silvery. But, there are other genes in other animals called "white spotting genes" that also cause this effect. Without genetic testing, it's hard to say for sure which one white-eye is, or why it has different phenotypes (speckled white across the eye markings, solid white circles, silvering on some birds but not others, etc). It could just be that it's a polygenic trait, as well.
However, for the sake of this guide, until proven otherwise, we are going to treat it as one gene with two different epigenetic modifiers. White-eye (WE) and white-eye with a silver modifier (WE^s which I will note as sWE for ease of typing). If there's ever genetic testing to look at the actual genes involved, I will update this guide.
However, for the sake of this guide, until proven otherwise, we are going to treat it as one gene with two different epigenetic modifiers. White-eye (WE) and white-eye with a silver modifier (WE^s which I will note as sWE for ease of typing). If there's ever genetic testing to look at the actual genes involved, I will update this guide.
Which genes are leucistic?
White and pied are leucistic genes, and are alleles of one another. This means that they replace one another on the same locus. We know that this is the case because of how Pied breeds, and because of how pied is created from scratch.
A visually white bird has the genotype WW- two copies of the white gene.
A visually pied bird has the genotype Wp- one copy of the white gene, and one copy of the pied gene.
A visually normal bird with white flights may be dark pied (pp), blue het white (WT/W), or blue het pied (WT/p). There are some reports that blue het white eye (WT/WE) also can appear with white flights, but I have not seen this confirmed personally.
Silver pied is an interaction of the white gene (W), the pied gene (p), and a white eye gene with the silver modifier (sWE). The genotype would look like W/p:sWe/sWE.
White bred to white will always produce white.
Dark pied bred to dark pied will always produce dark pied.
Pied or Silver pied does not breed true, and produces a range of genotypes/phenotypes- 25% white, 50% pied (or silver pied), and 25% dark pied (or dark pied white eye).
White bred to dark pied produces 100% pied. This makes knowing the parentage of your birds very useful, if you want to produce all the same bird in your offspring.
A visually white bird has the genotype WW- two copies of the white gene.
A visually pied bird has the genotype Wp- one copy of the white gene, and one copy of the pied gene.
A visually normal bird with white flights may be dark pied (pp), blue het white (WT/W), or blue het pied (WT/p). There are some reports that blue het white eye (WT/WE) also can appear with white flights, but I have not seen this confirmed personally.
Silver pied is an interaction of the white gene (W), the pied gene (p), and a white eye gene with the silver modifier (sWE). The genotype would look like W/p:sWe/sWE.
White bred to white will always produce white.
Dark pied bred to dark pied will always produce dark pied.
Pied or Silver pied does not breed true, and produces a range of genotypes/phenotypes- 25% white, 50% pied (or silver pied), and 25% dark pied (or dark pied white eye).
White bred to dark pied produces 100% pied. This makes knowing the parentage of your birds very useful, if you want to produce all the same bird in your offspring.
Leucistic Genetics
White
We will start with the easiest one first: white. White is an incomplete dominant gene. In heterozygous form, it (sometimes) shows with white flights and/or a white throat latch. It shares this phenotype with het pied and homo pied, and cannot be visually differentiated. In homozygous form, it turns the entire bird white.*
- *There are some reported cases of whites showing a feather, or even a few feathers, that have color. This is because white is NOT a color or a pattern. Those feathers are a result of pigment cells that succeeded in migrating to the correct location during development. OFTEN these spots will disappear over time, as the pigment cells have been weakened and die off. White birds with color coming through likely have weak leucism genes, and consideration for whether a breeder wishes to pass on such weakness should be made before breeding.
As you can see, nothing fancy. It moves like a regular autosomal recessive. All of the birds are blue. However! These birds may have white flight feathers or a white throat latch in their phenotype!
White also works the same as an autosomal recessive when bred to a split, except that because it's an incomplete dominant, it may show in the phenotype even in het form!
White also works the same as an autosomal recessive when bred to a split, except that because it's an incomplete dominant, it may show in the phenotype even in het form!
As you can see, half the offspring will be white, and half the offspring will be het white. HOWEVER. Again, those het whites may have phenotype differences, they may not look completely normal, because they aren't.
Let's look at het white x het white, and then we'll move to the trickier stuff with regards to white.
Let's look at het white x het white, and then we'll move to the trickier stuff with regards to white.
Again, pretty straightforward and on paper it looks like a regular autosomal recessive. But because it shows in het form, it's actually an incomplete dominant. Actual recessives CANNOT show in het form- it's why they are classified as recessives.
So now that you understand the way white works on its own with regards to the wild type, let's take a look at how it "masks" other colors. For the first table, let's look at a white x bronze breeding. This is a white out of wild types, and a bronze with no other mutations. Since we're tracking multiple mutations again, whip out your colon markers or go brush up on Genetics 203 if you need to.
So now that you understand the way white works on its own with regards to the wild type, let's take a look at how it "masks" other colors. For the first table, let's look at a white x bronze breeding. This is a white out of wild types, and a bronze with no other mutations. Since we're tracking multiple mutations again, whip out your colon markers or go brush up on Genetics 203 if you need to.
Again, nothing particularly special here! It looks like it works like any other autosomal "color" would, and produces all blue offspring when bred to a non-same color. Except (you guessed it) all the babies could have white flights or throat latches.
However, not all white birds are created equal. Remember that leucism does not change the color genes, it only alters the development of pigment cells, so color cannot be deposited on the feathers. But that doesn't change what color genes the bird has!
Here is a white (out of bronze) when bred to a bronze bird. Bear in mind that this white looks IDENTICAL to any other white in existence, by phenotype...
However, not all white birds are created equal. Remember that leucism does not change the color genes, it only alters the development of pigment cells, so color cannot be deposited on the feathers. But that doesn't change what color genes the bird has!
Here is a white (out of bronze) when bred to a bronze bird. Bear in mind that this white looks IDENTICAL to any other white in existence, by phenotype...
...and yet all the offspring are bronze!
This is because that "white" bird is actually a bronze bird being affected by total leucism. The leucism masks what the bird's phenotype would have been, if it had the ability to deposit pigment.
It will work the same with whites that are sex-linked colors as well. Here is a white (out of purple) cock bred to a wild type hen.
This is because that "white" bird is actually a bronze bird being affected by total leucism. The leucism masks what the bird's phenotype would have been, if it had the ability to deposit pigment.
It will work the same with whites that are sex-linked colors as well. Here is a white (out of purple) cock bred to a wild type hen.
Unlike a blue het purple bird, which would not show purple in the phenotype either, ALL of the hen offspring in this case would be purple without there being a visually purple bird present. But because the leucism "masks" the purple that would show, we get the same result as if the bird was purple visually. And (of course) all of the babies would possibly have white flights/throat latches to show they carry a leucistic gene.
As a last example, let's take a het purple het white male from above and breed him to one of the bronze het white hens from the previous table, and see what we get. Remember there are NO phenotypically white birds in this scenario- this is a blue phenotype bred to a bronze phenotype, but watch what happens:
As a last example, let's take a het purple het white male from above and breed him to one of the bronze het white hens from the previous table, and see what we get. Remember there are NO phenotypically white birds in this scenario- this is a blue phenotype bred to a bronze phenotype, but watch what happens:
Your hens will be 50% white hens, and 50% of the non-white hens will be purple. However, what you won't SEE is that 50% of the WHITE hens (bottom right corner) are also genetically purple. Not carrying, they ARE purple. They just can't display it because of the leucism.
So, even though white looks simple on the surface, you can see there may be a lot going on under the hood, so to speak. White does not (and CANNOT) co-express the way peafowl colors can, as it isn't actually a color gene, and its mechanism of function is completely different from theirs. The only time white co-expresses is with the other leucistic genes. Let's have a look at how.
So, even though white looks simple on the surface, you can see there may be a lot going on under the hood, so to speak. White does not (and CANNOT) co-express the way peafowl colors can, as it isn't actually a color gene, and its mechanism of function is completely different from theirs. The only time white co-expresses is with the other leucistic genes. Let's have a look at how.
Pied
When you hear the term 'pied' what you think of is a colored bird with white patches on it. This coloration is the "pied" phenotype. But pied, the gene, cannot create that phenotype on its own. When we talk about pied here, I will be referencing the GENE, not the phenotype, unless I have explicitly said phenotype.
The pied gene is the only truly dominant gene we know of in peafowl. To be considered a dominant gene, the gene must a) express in the phenotype even in single form and b) express the same in heterozygous form as in homozygous form. Both of these are true for pied. Like white, pied expresses in het form by white flights and a white throat latch. Unlike white, pied expresses the same in het form as in homo form- even in homozygous form, the bird only has white flights and a white throat latch, not large patches of white.
Because of this expression where most of the bird remains colored, homozygous pied is colloquially called "dark pied." It's not a great name for it, because in other animals a dark pied would be an animal with low pied expression, where a "loud" pied would be an animal with high pied expression. But, in other animals, their pied gene works straightforward- two pied genes makes a pied phenotype with patches of white in the phenotype. It's just not like that in peafowl, however. We have loud pied peafowl, but dark pied is NOT just a low-expression bird- it's the name of a genotype: p/p.
So what DOES make the pied phenotype? As discussed at the beginning of this page: a white gene. When white and pied interact, they co-express and create the pied phenotype. Since the two are alleles, the white gene would replace one of the pied genes, for a W/p genotype. Because of this, the pied phenotype does not breed true!
Let's look at why that is, by looking at the genes of pied x pied.
The pied gene is the only truly dominant gene we know of in peafowl. To be considered a dominant gene, the gene must a) express in the phenotype even in single form and b) express the same in heterozygous form as in homozygous form. Both of these are true for pied. Like white, pied expresses in het form by white flights and a white throat latch. Unlike white, pied expresses the same in het form as in homo form- even in homozygous form, the bird only has white flights and a white throat latch, not large patches of white.
Because of this expression where most of the bird remains colored, homozygous pied is colloquially called "dark pied." It's not a great name for it, because in other animals a dark pied would be an animal with low pied expression, where a "loud" pied would be an animal with high pied expression. But, in other animals, their pied gene works straightforward- two pied genes makes a pied phenotype with patches of white in the phenotype. It's just not like that in peafowl, however. We have loud pied peafowl, but dark pied is NOT just a low-expression bird- it's the name of a genotype: p/p.
So what DOES make the pied phenotype? As discussed at the beginning of this page: a white gene. When white and pied interact, they co-express and create the pied phenotype. Since the two are alleles, the white gene would replace one of the pied genes, for a W/p genotype. Because of this, the pied phenotype does not breed true!
Let's look at why that is, by looking at the genes of pied x pied.
As you can see, 25% of the offspring (upper left) will be WW. Just like any homozygous gene, there's no colon between them because they are on the same locus. The upper right and lower left boxes represent 50% of the offspring, and they are pied, Wp. Notice that even though the letters are not the same, indicating different genes, there's no colon- this is because the two are alleles, and exist on the same locus, just like if the W was a p or the p was a W. Lastly, 25% of the offspring will be dark pied, pp.
Even though the two parents are both the same phenotype, because the genes involved are not all the same genes, the offspring won't all be the same as the parents.
This difference in genes also means that if you only have one pied phenotype parent, the offspring cannot for sure be said to be "split pied." MANY people make this mistake, and say "split pied" when what they are trying to communicate is that one parent was the pied phenotype. Let's look at why, by breeding a pied parent to a wild type.
Even though the two parents are both the same phenotype, because the genes involved are not all the same genes, the offspring won't all be the same as the parents.
This difference in genes also means that if you only have one pied phenotype parent, the offspring cannot for sure be said to be "split pied." MANY people make this mistake, and say "split pied" when what they are trying to communicate is that one parent was the pied phenotype. Let's look at why, by breeding a pied parent to a wild type.
As you can see, NOT all of the offspring are het pied. Only half of them are het pied, the other half are het white. Visually, they may look exactly the same, so the only way to for-sure tell which one you have, would be to breed one to a white. We'll have a look at that next. For one last note, to get around saying "split pied" when you have only one single pied parent, you can say "split leucistic."
Breeding White and Pied Together
Since the pied phenotype contains white as a part of it, breeding it to white also means you don't get the wild type. This is how we know they are alleles- if white and pied were not alleles, breeding white to pied would produce the wild type.
So let's have a look at what happens when white is bred to pied.
So let's have a look at what happens when white is bred to pied.
As you can see, half the offspring will be white, and half the offspring will be pied phenotype. None of the offspring will be dark pied, however. This is one of the easier pairings to make, if you want to avoid the dark pied phenotype, or hets.
So what happens if you breed a het white to a het pied? Let's have a look.
So what happens if you breed a het white to a het pied? Let's have a look.
As you can see, 25% of the offspring are true wild types, 25% are het pied, 25% are het white, and 25% are pied! Again, with the hets you would likely see white flights/throat latches, and you would need to breed to a white to tell which is which. That being said, not all het white or het pied birds have white flights or throat latches. Some of them have NO outward indicator. So even the ones with no white may be hets. There's no way to tell for sure without breeding to a white. This makes keeping offspring from a breeding like the above kind of sticky, as you can't truly say who is split to what, or if they're clean or not.
Next up, let's look at het pied x white and how it differs from the above.
Next up, let's look at het pied x white and how it differs from the above.
As you can see, that one extra white gene drastically changes the genetic outcome. From 75% uncertain genotypes, you now have a simple 50% pied, 50% het white spread of babies.
But what about the other way around? Let's look at pied x het white
But what about the other way around? Let's look at pied x het white
Even though one of the birds is a "full" mutation (not a het/split bird), you still end up uncertain about half the offspring, which may be het white, or het pied, with no way to tell the difference without breeding them to a white. But, you get more variance in the known offspring, producing white and pied.
Dark Pied
So far we've only looked at pied and het pied, where the bird only has one copy of pied. This is because the pied gene has some weird circumstances surrounding its homozygous form. The homozygous form is called "dark pied." Despite "pied" being in the name, these birds can present with absolutely no white feathers at all. The name should go out of style, because it's confusing, but we work with what we have.
However, please remember that "dark pied" is the description of a phenotype that's a specific genotype. It's not a new or separate gene, it's homozygous pied. This means there is no "het dark pied" genotype. That's just split pied. So, we're only going to go over a few breedings using dark pied.
Since dark pied is a homozygous genotype, it will breed true when bred to itself.
Dark pied x Dark pied
However, please remember that "dark pied" is the description of a phenotype that's a specific genotype. It's not a new or separate gene, it's homozygous pied. This means there is no "het dark pied" genotype. That's just split pied. So, we're only going to go over a few breedings using dark pied.
Since dark pied is a homozygous genotype, it will breed true when bred to itself.
Dark pied x Dark pied
Since dark pied is homozygous pied, it can be used to create a pairing which produces 100% pied offspring. This is useful if you're trying to create a lot of pied birds, but it means your breeders won't look pied. The fact that white x dark pied will make 100% pied is how we know that the pied phenotype is a heterozygote, and that it's made of the white and pied alleles.
A dark pied bird will also never produce white offspring when paired to a pied. This is one of the ways we know when a bird is NOT het white, despite that het white looks the same as het pied/homo pied. But, you will get 50% pied when breeding dark pied x pied.
And that should cover what you need to know about the pied gene!
White Eye
White eye describes the phenotype where the eye markings on a bird change from black to white. White eye has variable expression and sometimes expresses in the phenotype even in single copy. Sometimes the white eye markings are speckled white, sometimes the marking is a clean-edged mark in the center of the eye. Sometimes the white eye markings are confined to the train feathers, sometimes the markings appear on the tips of body feathers. Sometimes it causes a dusty, silvery coating over the whole bird, called "frosting." This variance is likely due to various epigenetic modifiers to the gene, and seems to be heritable.
NOT all white eye genes are created equal. Those epigenetic factors can cause major differences in the phenotype when they interact with other leucistic genes. A bird that is pied + white eye may be pied white eye or silver pied, depending on which type of white eye gene was inherited. Because even a het white eye bird can express white eye/silvering, a silver pied bird may only have one silver white eye gene and one normal white eye gene, and produce regular pied white eye offspring.
White eye travels like any other autosomal gene, so I won't do Punnett squares for it; the major complication for it is in the phenoytpe, not the genotype.
NOT all white eye genes are created equal. Those epigenetic factors can cause major differences in the phenotype when they interact with other leucistic genes. A bird that is pied + white eye may be pied white eye or silver pied, depending on which type of white eye gene was inherited. Because even a het white eye bird can express white eye/silvering, a silver pied bird may only have one silver white eye gene and one normal white eye gene, and produce regular pied white eye offspring.
White eye travels like any other autosomal gene, so I won't do Punnett squares for it; the major complication for it is in the phenoytpe, not the genotype.
Silver Pied
The silver pied phenotype is comprised of one white gene, one pied gene, and two white eye genes that have the silvering modifier. To be considered silver pied, the bird MUST have silvering, otherwise it is simply a pied white eye bird. Some people also don't consider the bird to be silver pied unless white covers 80%+ of the bird's body, but no one has a good way to quantify the percentage of white. No one is measuring to see if a bird is only 79% white. But silvering you can easily tell if it is present or not, and if it isn't present, then the bird isn't silver pied.
As stated earlier, silver pied is a polygenic phenotype, which means it's a description of how a bird looks, and does not describe a single mutant gene. As we've seen in earlier lessons, "Bronze" for example describes a bird homozygous for the bronze mutant gene, but "Platinum" describes a bird that's homozygous for the bronze mutant gene AND homozygous for the opal mutant gene. There is not a platinum gene. Similarly, there is no "silver pied" gene. A bird cannot be "split silver pied" because of this.
Let's look at why, by pairing a silver pied bird with a wild type.
As stated earlier, silver pied is a polygenic phenotype, which means it's a description of how a bird looks, and does not describe a single mutant gene. As we've seen in earlier lessons, "Bronze" for example describes a bird homozygous for the bronze mutant gene, but "Platinum" describes a bird that's homozygous for the bronze mutant gene AND homozygous for the opal mutant gene. There is not a platinum gene. Similarly, there is no "silver pied" gene. A bird cannot be "split silver pied" because of this.
Let's look at why, by pairing a silver pied bird with a wild type.
Since it's a polygenic mutation, we have to track the white and pied alleles, and then also the silver white eye gene. As you can see, the spread of offspring greatly resembles that of the pied x WT pairing we did earlier! And that's because it's the same pairing, with one extra gene. As you can see, there's no "silver pied" gene, and the offspring instead are either het white or het pied. Since true SP birds are homozygous for the silver white eye gene, all the offspring will also carry a single sWE gene.
Since silver pied is a version of pied, it also means that silver pied x silver pied will have the same 25/50/25% spread of offspring as pied x pied!
Since silver pied is a version of pied, it also means that silver pied x silver pied will have the same 25/50/25% spread of offspring as pied x pied!
So, silver pied will pair with white and dark pied very similarly to pied, just with the added silver white eye gene to track. Remember that with white, the parentage matters, and that's true here too- a white out of silver pied x silver pied will have two copies of silver white eye. It's also possible for a bird to be homozygous silver white eye without being silver pied. Just like with pied, breeding white (from silver pied x silver pied) and dark pied silver white eye (DP from SP x SP) will create 100% silver pied!
And that wraps up the leucistic mutations genetic lesson.
You can return to the main genetics page by clicking here!
And that wraps up the leucistic mutations genetic lesson.
You can return to the main genetics page by clicking here!