Multi-Gene Phenotypes
Some colors of peafowl are the result of multiple genes interacting with one another, and do not have genes of their own. A "platinum" color peafowl does not have a platinum gene; instead, it is homozygous for bronze AND homozygous for opal. When this happens, in some animals one mutation may be dominant over the other, but in others (and in peafowl), the colors co-express. This means both colors express in the phenotype at once, causing a new phenotype (platinum) that is not the same as either of the colors that comprise it (bronze or opal). Platinum is not the only color like this! Here are the others we know:
- Platinum (Bronze + Opal)
- Peach (Purple + Cameo) - This is a special case! See the section for "peach" below.
- Taupe (Purple + Opal)
- Mocha (Purple + Midnight)
- Ivory (Cameo + Opal)
- Hazel/Indigo (Purple + Bronze) - This is another weird case. In this case, two phenotypes share the same genotype, with variance in expression.
- Rosewood (genes unknown)
- Amethyst (genes unknown)
Completely Autosomal Phenotypes
To start a little easier, we look at the only completely autosomal phenotype that has multiple color genes: Platinum. As stated above, platinum is a combination of bronze + opal. A platinum genotype would include "br/br:o/o" as part of it. As you can see, there is not a "platinum" gene, and as such no bird can be "split platinum." Instead, they would be split bronze and split opal.
Normally when we split genes to go into a Punnett square, we split them into single genes (o/o becomes o and o), like this:
Normally when we split genes to go into a Punnett square, we split them into single genes (o/o becomes o and o), like this:
The "o" gene is on the same locus as the wild type gene that goes in that place, so it replaces the wild type gene and you only need one gene in the parent box. This can also occur with mutations (white and pied are on the same locus, and replace one another). However, when dealing with genes that are not in the same locus (and therefore are not alleles/do not replace one another), we have to ensure that all of the genes are represented. Do this by separating the chromosome pair with a slash (o/o) so that both chromosomes in a pair are represented in notation, and then we separate the loci with a colon (o/o:br/br) so that all mutations are represented.
In order to move this into a Punnett square, we must treat each section between the colon as its own thing, and split that section as if it does not have the other sections present. So, I've color coded the following squares to better illustrate it.
In order to move this into a Punnett square, we must treat each section between the colon as its own thing, and split that section as if it does not have the other sections present. So, I've color coded the following squares to better illustrate it.
Since the bird is homozygous for both genes, both genes always travel, and can go in the same box as one another. Now, in this instance, the genes do not need to go into the boxes in this color order; the orange "o" could have gone with the blue "br" and the red "o" could have gone with the green "br." The important thing is that all combinations of LETTERS (ie genes) are represented, not all colors of those letters (for example, you would not want to have "o/o:br" in a parent box). If you need a refresher beyond this on tracking multiple genes, please see Genetics 201.
Now that you remember how to split multiple genes into a Punnett Square, let's try that autosomal, multi-gene phenotype: Platinum x Platinum.
First we split the genotype into individual chromosomes in the parent squares:
Now that you remember how to split multiple genes into a Punnett Square, let's try that autosomal, multi-gene phenotype: Platinum x Platinum.
First we split the genotype into individual chromosomes in the parent squares:
And then we fill in the offspring boxes, the same as we would in a normal Punnett square, only this time we are pairing genes from the same side of the colon (this is why it's important to keep the genes in the same order for the parents). Fill in the left side of the colon first.
Then add a colon to move to the next chromosome, and fill in the next gene, taking one from dad's box and one from mom's box.
Then we do this for all the offspring boxes!
As you can see, all offspring will also be platinum.
Let's take a look at what happens when you breed a multi-gene phenotype to a wild type. Since this is autosomal only, we don't need to track sexes, but since there are two pairs of chromosomes we're tracking (one for bronze, one for opal), we need two wild type chromosome pairs to match the two genes we're tracking.
Let's take a look at what happens when you breed a multi-gene phenotype to a wild type. Since this is autosomal only, we don't need to track sexes, but since there are two pairs of chromosomes we're tracking (one for bronze, one for opal), we need two wild type chromosome pairs to match the two genes we're tracking.
And then we fill in each side of the color like before.
The genotype "WT/br:WT/o" is the same as a split bronze (WT/br) and split opal (WT/o), therefore the offspring are all split bronze and split opal. You can make this same bird breeding bronze x opal, instead of platinum x wild type.
Multi-gene phenotypes also have another special quality. Normally if you breed a color to a non-same color (example, bronze x opal), you would get all wild type phenotypes ("blues") that carry the colors of the parents. However, if you breed a multi-gene phenotype (like platinum) to one of it's component mutations (in this case, bronze or opal), you will get that second color.
Let's have a look at Platinum x Opal! Again, we want to keep the same number of chromosomes on each parent, so since opal is missing bronze in the bronze locus, we add a wild type pair of chromosomes.
Multi-gene phenotypes also have another special quality. Normally if you breed a color to a non-same color (example, bronze x opal), you would get all wild type phenotypes ("blues") that carry the colors of the parents. However, if you breed a multi-gene phenotype (like platinum) to one of it's component mutations (in this case, bronze or opal), you will get that second color.
Let's have a look at Platinum x Opal! Again, we want to keep the same number of chromosomes on each parent, so since opal is missing bronze in the bronze locus, we add a wild type pair of chromosomes.
In this case, all of the offspring are opal het bronze. This is because the opal gene is part of platinum, so offspring can get a copy from each parent. But, since Platinum requires homozygous bronze as well, none of the offspring will be platinum. The same is true any time a multi-gene bird is bred to ANY of its component genes (for example, if platinum is bred to bronze).
This same effect can happen when multi-gene birds are bred to split birds that have one of their component colors. Let's look at Platinum x Blue split Bronze.
This same effect can happen when multi-gene birds are bred to split birds that have one of their component colors. Let's look at Platinum x Blue split Bronze.
As you can see, all offspring are het for opal (which they got from their platinum parent), and all offspring have at least one bronze gene (which they got from their platinum parent). Since the het bronze parent only had one bronze gene, only half the offspring got 2 copies of bronze, and are bronze het opal.
Let's also have a look at what happens when a multi-gene phenotype is bred to a bird who is heterozygous for both of its component genes. In this case, a platinum bird bred to blue het bronze AND opal. You'll notice that this Punnett square has more offspring boxes than usual- that is because we are still making sure that all possible combinations of letters from the parent genotype are represented in the parent boxes. The split parent can donate two wild type genes (WT:WT), one bronze and one wild type gene (br:WT), one bronze and one opal gene (br:o), or one wild type and one opal gene (WT:o), so you need 4 parent gene boxes instead of just 2.
The platinum parent, as before, has the same pair of genes it can donate.
Let's also have a look at what happens when a multi-gene phenotype is bred to a bird who is heterozygous for both of its component genes. In this case, a platinum bird bred to blue het bronze AND opal. You'll notice that this Punnett square has more offspring boxes than usual- that is because we are still making sure that all possible combinations of letters from the parent genotype are represented in the parent boxes. The split parent can donate two wild type genes (WT:WT), one bronze and one wild type gene (br:WT), one bronze and one opal gene (br:o), or one wild type and one opal gene (WT:o), so you need 4 parent gene boxes instead of just 2.
The platinum parent, as before, has the same pair of genes it can donate.
We can see that this pairing produces blue het bronze and opal, bronze het opal, platinum, and opal het bronze. If you look at the number of boxes and the number of matching genotypes, we can see each of these results accounts for 25% of the total offspring.
You might be wondering why we write out the br:o two times on the platinum parent boxes, and the short answer is because we're still accounting for all combos of the genes the parent has, and it's easier to just do it every time than to figure out which times you actually need to and which times you don't, especially when you're learning. Leaving it out when it's actually needed can affect the percentages and accuracy of the offspring you predict.
The last autosomal-only example we'll have a look at is what happens when you breed to a full color component that is split to the other component. In this case, a platinum bred to a bronze het opal.
You might be wondering why we write out the br:o two times on the platinum parent boxes, and the short answer is because we're still accounting for all combos of the genes the parent has, and it's easier to just do it every time than to figure out which times you actually need to and which times you don't, especially when you're learning. Leaving it out when it's actually needed can affect the percentages and accuracy of the offspring you predict.
The last autosomal-only example we'll have a look at is what happens when you breed to a full color component that is split to the other component. In this case, a platinum bred to a bronze het opal.
In this case, half the offspring will be platinum (because the het parent has one copy of each of the genes needed for platinum) and half will be bronze het opal (because the het parent doesn't have two copies of both genes needed). This would be true regardless of which gene the parent is homozygous for and which gene the parent is het for, so if the parent had been opal het bronze, you would have still seen 50% platinum, but you'd see 50% opal instead of bronze.
We don't currently have any other known autosomal-only multi-gene phenotypes, but if and when someone produces them, they should work the same way as Platinum. You'd just simply replace the gene markers with the gene markers for the other colors. This also works if you're trying to predict outcomes for birds that don't exist yet, that you might be trying to make. Let's have a look at making one!
We don't currently have any other known autosomal-only multi-gene phenotypes, but if and when someone produces them, they should work the same way as Platinum. You'd just simply replace the gene markers with the gene markers for the other colors. This also works if you're trying to predict outcomes for birds that don't exist yet, that you might be trying to make. Let's have a look at making one!
Multi-gene Phenotypes with Sex-linked Inclusion
While we do not know which (if any) autosomal genes are on the same chromosome and/or in the same locus, we do know that no autosomal color is on the same chromosome as the sex-linked colors, because all sex-linked colors are on the Z sex chromosome and all autosomal colors are not- that's what makes them sex-linked or autosomal in nature.
That being said, the mutations with sex-linked genes are not quite all the same, and are a bit trickier, genetically, than anything we've discussed so far. We'll take the most straightforward ones first: Taupe, Mocha, and USA Ivory. These three behave as expected when breeding them, with no surprises.
Like with autosomal multi-gene phenotypes, normal sex-linked multi-gene phenotypes breed true. For example, if you breed Taupe x Taupe, you will get Taupe. However, unlike autosomal multi-gene phenotypes, you can get sex-linked hens from breeding a sex-linked multi-gene phenotype to a non-same color containing no component colors. What this means is if Taupe is opal + purple, and you breed it to any bird that isn't taupe, opal, purple, or split to opal or purple, you will still get purple hens, because purple is sex linked and purple is a component of taupe.
That being said, the mutations with sex-linked genes are not quite all the same, and are a bit trickier, genetically, than anything we've discussed so far. We'll take the most straightforward ones first: Taupe, Mocha, and USA Ivory. These three behave as expected when breeding them, with no surprises.
Like with autosomal multi-gene phenotypes, normal sex-linked multi-gene phenotypes breed true. For example, if you breed Taupe x Taupe, you will get Taupe. However, unlike autosomal multi-gene phenotypes, you can get sex-linked hens from breeding a sex-linked multi-gene phenotype to a non-same color containing no component colors. What this means is if Taupe is opal + purple, and you breed it to any bird that isn't taupe, opal, purple, or split to opal or purple, you will still get purple hens, because purple is sex linked and purple is a component of taupe.
This isn't true when breeding a wild type (or other non-component) male to a multi-gene sex-linked phenotype hen- in that case, all offspring would be blue het for the autosomal color, and males would be het for the sex linked color.
This is the same pattern of outcomes for mocha and US ivory as well.
Now, sex-linked multi-gene phenotypes act a little differently than autosomal multi-gene phenotypes when bred to the component colors. I will use Taupe again for the example. Let's look at a taupe cock x purple hen first, to see what happens when these phenotypes are bred to the sex-linked component color.
Now, sex-linked multi-gene phenotypes act a little differently than autosomal multi-gene phenotypes when bred to the component colors. I will use Taupe again for the example. Let's look at a taupe cock x purple hen first, to see what happens when these phenotypes are bred to the sex-linked component color.
Like autosomal multi-gene phenotypes, all the offspring will be the sex-linked component color (in this case, purple), and be het for opal.
It is the same for breeding a sex-linked component color cock (in this case purple) to the sex-linked multi-gene phenotype (taupe) hen- all offspring will still be the sex-linked color (purple in this case).
It is the same for breeding a sex-linked component color cock (in this case purple) to the sex-linked multi-gene phenotype (taupe) hen- all offspring will still be the sex-linked color (purple in this case).
It will ALSO behave the same if you breed a multi-gene sex-linked phenotype (taupe) to the autosomal component hen (in this case, opal)- you will get the same phenotype results as the autosomal multi-expression phenotypes.
HOWEVER! You will NOT get the same results as autosomal-only multi-gene phenotype when it comes to breeding multi-gene sex-linked phenotype (taupe) cock to the autosomal component (opal) hen. With autosomal-only, all offspring would be the autosomal component color. However, since sex-linked color males produce their color hens regardless of mate, you will get full multi-gene phenotype hens.
So that covers the basics for sex-linked mulitg-gene phenotype breeding. Any new phenotypes that involve one autosomal and one sex linked color should behave the same way as these.
Exception #1 - Hazel and Indigo
Hazel and Indigo, by genotype, are both homozygous bronze and homozygous purple. The gene transference works like above, but the phenotype of the offspring may be that of hazel or that of indigo, seemingly at random. Breeding hazel x hazel may produce both hazel and indigo, and breeding indigo x indigo may produce both indigo and hazel.
We do not have an explanation for this, its just something you have to bear in mind as an exception to the rules.
We do not have an explanation for this, its just something you have to bear in mind as an exception to the rules.
Exception #2 - Peach
Peach is unlike any other color or pattern or leucistic mutation, and merits its own section for explaining it.
The peach phenotype is the result of chromosomal crossover. Basically, once egg and sperm connect and begin to exchange genetic coding, there's a brief phase where non-linear mixing of genetic code can occur (ie, genetic code gets placed on the opposite chromosome of the pair rather than the one it was intended for). In the case of peach, when a purple and a cameo were bred together instead of transferring purple to one Z and cameo to the other Z, crossover occurred in a very specific way that placed both mutations on the same Z.
A bird whose Z chromosomes all have both purple and cameo on them will display the phenotype we call Peach.
Peach is unique because although it is composed of purple + cameo, the purple and cameo genes cannot be separated again- kind of. On very rare occasion, a crossover event could undo the combination, removing one of the genes from the chromosome. However, typically peach cannot be separated into purple and cameo, and so must be treated both as a single gene and as a multi-gene.
It is also true that a typical breeding of cameo x purple will NOT result in peach. Before we get into the actual peach genetics, let's look at why cameo x purple will not produce peach.
Here is what happens when you breed a purple cock to a cameo hen:
The peach phenotype is the result of chromosomal crossover. Basically, once egg and sperm connect and begin to exchange genetic coding, there's a brief phase where non-linear mixing of genetic code can occur (ie, genetic code gets placed on the opposite chromosome of the pair rather than the one it was intended for). In the case of peach, when a purple and a cameo were bred together instead of transferring purple to one Z and cameo to the other Z, crossover occurred in a very specific way that placed both mutations on the same Z.
A bird whose Z chromosomes all have both purple and cameo on them will display the phenotype we call Peach.
Peach is unique because although it is composed of purple + cameo, the purple and cameo genes cannot be separated again- kind of. On very rare occasion, a crossover event could undo the combination, removing one of the genes from the chromosome. However, typically peach cannot be separated into purple and cameo, and so must be treated both as a single gene and as a multi-gene.
It is also true that a typical breeding of cameo x purple will NOT result in peach. Before we get into the actual peach genetics, let's look at why cameo x purple will not produce peach.
Here is what happens when you breed a purple cock to a cameo hen:
As you can see, no peach. What about the other way around, with a cameo cock and a purple hen?
Still no peach. You could breed purple and cameo together in any combination, including splits, and still never have a bird that experiences the exact right crossover event to combine them. This means you cannot purposely make peach from scratch, the way you can with other multi-gene phenotypes.
So, now that we know we can't make peach from scratch on purpose, let's look at how Peach happened. Modeled below is an example of what happens in the case of chromosomal crossover.
So, now that we know we can't make peach from scratch on purpose, let's look at how Peach happened. Modeled below is an example of what happens in the case of chromosomal crossover.
In the first square of the offspring, you can see 1 cameo mutation has migrated off of the Z it was on, and landed on the other Z, creating a "peach" Z chromosome (and making the other Z a normal blue).
This will not actually happen in one quarter of offspring! This is a one-in-a-million random chance occurrence. By looking at historical records of the spread of peach, I believe it has appeared twice from scratch- one in a chromosomal crossover event (the peach hens that appeared at Legg's from a purple hen) and one fresh mutation (peach from a full cameo pen, where purple may have mutated freshly- purple is likely a simple melanin dilute, a kind of mutation that happens often).
Visually this rare male from the chart will be the same as his brothers, who are blue split purple/cameo. You would only know this happened when the male that experienced crossover is bred, and half of his female offspring come out peach. This will be indistinguishable from a male who just happened to be het from an already-established peach bloodline, so there's no longer a sound way to know if a chromosomal event has occurred or if your bird was just split.
As I said at the beginning, the same thing can happen in reverse as well- the kind of event which added the gene to the opposite Z can remove it, resulting in blue, purple, or cameo offspring from peach x peach. This is rare as well, and not the typical outcome.
This will not actually happen in one quarter of offspring! This is a one-in-a-million random chance occurrence. By looking at historical records of the spread of peach, I believe it has appeared twice from scratch- one in a chromosomal crossover event (the peach hens that appeared at Legg's from a purple hen) and one fresh mutation (peach from a full cameo pen, where purple may have mutated freshly- purple is likely a simple melanin dilute, a kind of mutation that happens often).
Visually this rare male from the chart will be the same as his brothers, who are blue split purple/cameo. You would only know this happened when the male that experienced crossover is bred, and half of his female offspring come out peach. This will be indistinguishable from a male who just happened to be het from an already-established peach bloodline, so there's no longer a sound way to know if a chromosomal event has occurred or if your bird was just split.
As I said at the beginning, the same thing can happen in reverse as well- the kind of event which added the gene to the opposite Z can remove it, resulting in blue, purple, or cameo offspring from peach x peach. This is rare as well, and not the typical outcome.
So now that we know how peach occurred and why you can't just make it, we can have a look at how it transfers. Please bear in mind that because Peach is a weird exception (the ONLY multi-sex-linked-gene phenotype, rather than a mixed autosomal + sex-linked phenotype), these are only the expected, most common outcomes, and that the exceptions discussed above can still occur. However, they're so unlikely that you will probably not experience them.
Even though Peach is technically a combo of two genes, it travels like a single gene. Let's look at peach male x wild type. Remember that all genes within the parenthesis must travel with the Z they are attached to.
Even though Peach is technically a combo of two genes, it travels like a single gene. Let's look at peach male x wild type. Remember that all genes within the parenthesis must travel with the Z they are attached to.
This very closely resembles the way a normal, single-gene sex link works! The difference is you can see two genes on the Z chromosome instead of one. It will also travel the same way as a single-gene sex-link if you breed a peach hen to a wild type male, like in the chart below.
However, it will also act like a normal multi-gene phenotype when bred to its component colors! Let's look at peach male x purple hen:
Like with any sex link, the male always gives his daughters his color, and like a normal dual color bred to its component colors, the males are the component color.
With a peach hen x purple male (or cameo male), the offspring would all be purple (or cameo, depending on which male was used).
With a peach hen x purple male (or cameo male), the offspring would all be purple (or cameo, depending on which male was used).
If you look at the above chart, the top offspring row contains a special kind of bird: Z(pl)Z(pl:c). Some people will call this "purple split cameo" but this is kind of a misnomer, as the cameo cannot be purposely separated from the purple on its chromosome. However, there is no "peach" gene (since peach is a combination of other genes), so "purple split peach" is not technically accurate either. That said, "purple split peach" is a slightly easier concept when trying to communicate what the bird is, genetically, and slightly more accurate as to how the genes travel.
And that's everything for multi-gene phenotype colors! This page has ONLY covered colors; the next two lessons will cover patterns and leucistic mutations, and the last page will have test breedings folks have asked me to do with many genes at once.
Head back to Peafowl Genetics main page!
Head back to Peafowl Genetics main page!