Turkey Color Genetics Lessons

[Lagerdogger]

Introduction

Genetics is the science of how traits are passed from one generation to another. Turkey color genetics questions are common on this site, and some people have asked for a guide to color genetics. Hopefully this thread will be a useful reference. I will create another thread called "Turkey Genetics Feedback" where you can ask questions, complain, correct inaccuracies, or boo me off the stage. Please use the feedback thread for comments so people don’t have to look to hard to find a topic they may be interested in. There are still some genetic combinations that I don't fully appreciate yet, and I will stay away from these or simply say I don’t know (another chance to provide feedback).

I will start with a brief discussion of basic genetics, then talk about the standard bronze, then discuss how different colors are produced by deviating from the bronze. My vision is that by the end of this series, everyone will know how to cross different strains to intentionally raise any color of turkey they want.

So, here we go.

Lesson 1. Basic Genetics

To understand how turkey colors are determined, we need to start with a basic understanding of genetics. Genetics is the study of how traits (such as eye color in people) are passed from one generation to the next. This next section will introduce a lot of terminology. You will not have to remember all the terms to understand color determination, but it is presented here for background. This will be the longest, hardest, and least interesting of the lessons, but will help you to understand future lessons. I have presented a summary in advance to help you know where we are going.

Summary
Genes are found at particular spots on chromosomes called loci (plural of locus).
There are two genes that define every trait. One gene came from the father and one from the mother.
Genes usually come in dominant recessive allele pairs. Dominant alleles (genes) express themselves even if only one dominant gene is present. Dominant traits get capital letters, such as B, while recessive traits get lower case of the same letter, b.
There may be more than two alleles for a given trait.
Dominance may be incomplete.

A gene is a part of a strand of DNA. Genes are strung together into long strands of DNA called chromosomes. Chromosomes are paired, and each half of the pair of each chromosome has a set of genes for the same traits. In other words, if one half of a chromosome has genes for eye color, hair color, and skin pigment, then the other half of that chromosome also has genes for eye color, hair color, and skin pigment. One strand of each chromosome comes from each parent.

The location of a gene on the chromosome is called the locus. The genetic information for eye color in people is always at the same location on the same chromosome. It is always at the same locus.

The form of the gene is called an allele. Again, for human eye color, there are two basic alleles, one for blue eyes and one for brown eyes. The alleles are not always the same. If one parent has two alleles for brown eyes, and one parent has two alleles for blue eyes, the offspring will all have one brown eye allele and one blue eye allele. The term allele is often replaced with the word gene.

Most genes come in dominant/recessive pairs. In other words, there are two possible alleles for any one locus, and one is dominant over the other. It expresses itself even when both alleles are present. For human eye color, brown eye genes are dominant to blue eye genes, so people with one brown gene and one blue gene have brown eyes, just like people with two brown genes. Only people with two blue genes have blue eyes. Dominant recessive pairs are usually written with using the same letter, with the dominant gene capitalized. So B is used for brown eye genes, and b is used for blue eye genes. Someone with two brown eye genes would be describes as BB, and someone with two blue eyed genes would be described as bb. These combinations are called homozygous (two of the same allele). Someone with one of each would be described as Bb (heterozygous, meaning two different alleles).

Eye color is nice and simple because there are only two alleles, and one is completely dominant to the other. Some genes have more than two alleles, and there may be a chain of dominance, like a pecking order. The next lesson will have a turkey example involving three possible alleles at a locus. Also, dominance is not always complete. For example, if you cross a red snapdragon with a white snapdragon, you get a pink snapdragon. In this case, the red flower is RR (red gene, red gene), the white flower is rr (not red, not red), and the pink flower is Rr (red, not red). With incomplete dominance, one red gene and one not red gene makes the flower half red, or pink. Incomplete dominance will come up later.
I think this will be enough to get us started.

Summary
Genes are found at particular spots on chromosomes called loci (plural of locus).
There are two genes that define every trait. One gene came from the father and one from the mother.
Genes usually come in dominant recessive pairs. Dominant genes express themselves even if only one dominant gene is present.
There may be more than two genes for a given trait.
Dominance may be incomplete.

 

[Steve_of_sandspoultry]

delete

 

[Lagerdogger]

Lesson 2 – Base Colors - Standard Bronze, Black, and Black-winged Bronze

There are basically two types of genes that go into determining turkey color. The first of these is the base color, and the second are modifying colors. In this lesson we will talk about base colors, then add on modifying colors as things get more involved in later lessons.

The standard bronze is a bronze-based bird with no modifying color genes. It is homozygous bb for the base color. It is often written as b+b+, where the + indicates that we recognize that there are other modifying genes, but that none of them are doing anything. This will become clearer when we start to talk about modifying genes.

You may have noticed that the bronze base color is denoted as lower case bb. Recall from lesson 1 that lower case letters are usually recessive. In this case, the bronze based genes are recessive to black based genes. So a turkey that is BB or Bb will be a black turkey.

The base color genes are also interesting in that there are three choices for alleles, not just two. The third base color choice is black-winged bronze, denoted as b1. Black-winged genes are semi-recessive to both bronze based. So to be black-winged bronze, the bird must have two black-wing bronze base genes, written as b1b1. A bird that is Bb1 is black, and a bird that is bb1 looks like a standard bronze.

The reason I called the b1 semi-recessive to b is that in my birds that are bb1, the barring does not appear to be as bold or as well defined as in bb turkeys. My bb1 birds are still only about 9 weeks old, and the barring may change as they mature, so I will keep an eye on this and edit if needed. (If you have pictures of adult primaries from bb1 birds, post them on the turkey genetics feedback thread).

By the way, it is customary to write the dominant gene first, so a bird that is heterozygous for black based and bronze based would always be written as Bb, not bB.

 

[Lagerdogger]

Quote:
I think Steve's point here is that breeding involves more than just color of the bird. There are conformation aspects, standard weights, maintaining lines, etc. All I am trying to do here is talk about how the different colors come about. There are several websites that discuss the genetics of turkey color. Porter's Turkeys is a great reference and the easiest one to read, but still leaves some things unexplained to the novice. My goal here is that people who read this thread will be able to look at the genetics of a golden phoenix and see that it is really a black-winged golden narragansett with a gray gene, and they will be able to undersatnd why they wil not breed true, and then they will be able to not only identify the colors that will be produced, but also calculate the average proportion of each color.

I am hoping this will be fun for those who want to learn something they don't yet know.

 

[mochicken]

Thanks for sharing, I have breed snakes, bearded dragons, and lizards over the years and have learned alot about genetics and "het" for genetics in them but never even imagined that turkey breeds and colors were so dependent on genetics, seen or unseen in the "parents"

Thanks for sharing, this should definitely answer a few questions

 

[Lagerdogger]

Lesson 3 –Red Genes: Bourbon Red and Red Bronze

Bourbon Reds are bronze-based birds. What makes then red is that they have two red modifying genes. The red genes are recessive to the dominant “not red” genes, so red is denoted as r and “not red” is denoted as R.

So a Standard Bronze, normally written as b+b+ could also be written as bbRR, a bronze based bird with two dominant “not red” genes. A Bourbon Red would then be written as bbrr, a bronze based bird with two recessive red genes.

Bourbon reds breed true. This is because they are homozygous at all loci (they always have two of the same genes for every color). When they breed, the tom donates a bronze gene and a red gene…br. Then hen also donates a bronze gene and a red gene...br. When combined, there are always two bronze genes and two red genes…bbrr. So bourbon reds crossed with bourbon reds always give bourbon reds.

What happens if, at the red gene position (the red locus), you get a “not red” and a red gene, such as bbRr. If R was completely dominant to r, the bird would look like a standard bronze. But the red genes display what is called incomplete dominance. In other words, one red gene will affect the appearance of the bird, but not as much as two red genes. The result is a Red Bronze turkey. If you cross a Standard Bronze, bbRR with a Bourbon Red, bbrr, all of the offspring will be Red Bronze bbRr. The bronze always contributes bR, and the bourbon red always contributes br, for a poult that is bbRr.

So what happens when you cross back two red bronzes? The tom will contribute a “not red” gene to half its offspring, and a red gene to the other half. The hen will do the same thing, so half of the birds that have an R from the father get an R from the mother, while half of the birds that get an R from the father get an r from the mother. The offspring with r from the father also get half R and half r from the mother. So if we write out the genetic makeup of the offspring, with the father’s gene written first, we have
25% bbRR
25% bbRr
25% bbrR, and
25% bbrr

Since bbRr and bbrR are the same, 25% of the offspring will be standard bronze bbRR, 50% will be red bronze bbRr, and 25% will be bourbon red bbrr. These percentages are statistical averages and actual results may vary.

We see that red bronze do not breed true. Whenever you see heterozygosity (different genes for any particular color), the offspring will not breed true. If there are only two genes (in the case red and not red), then half the offspring will get one of each gene, 25% will have two of one of the genes, and 25% will have two of the other genes.

In this picture of young turkeys, there is a bourbon red on the far left, then a red bronze, then a standard bronze: two red genes, one red gene, no red genes.

 

[Lagerdogger]

Lesson 4: Narragansetts

Just like bourbon reds are standard bronze with two recessive red genes, Narragansetts are standard bronze with two recessive Narragansett genes. Narragansett genes are written as ng, while “not Narragansett is written Ng. So a standard bronze could be written b+b+NgNg, while a Narragansett is b+b+ngng.

Narragansett genes tend to lighten up whatever color is already present. They turn bronze birds into the typical gray Narragansett, red bronze into golden Narragansett, and sweetgrass into royal palms.

But the most interesting thing about Narragansett genes is that they are sex-linked. So if you cross a standard bronze hen with a Narragansett tom, the bronze donates b+Ng, and the Narrgansett donates b+ng. The result is that all the tom poults are b+b+Ngng, and look like bronzes, while all the hens are b+b+ng— and look like Narragansetts (the hyphen indicates only one Narragansett gene in the females). You can accurately sex this cross at about three weeks when the colors start to show.

In the follwoing photos, the color genes are identical in both birds. They each have a single red and a single Narragansett gene. The lighter color of the hen is the Narragansett gene being expressed. If the tom had two Narragansett genes, it would be colored like the hen, and if the hen had no Narragansett gene, it would be darker like the tom.

Tom - looks red bronze

Hen - looks golden Narragansett

 

[Lagerdogger]

Lesson 5 – Whites, Grays, and Palms

The dominant “not white gene is C, while the recessive white gene is c. The white genes make birds white, regardless of what the base pair is. So a BBcc is white, even though its base is black, and a bbcc bird is also white. Kevin Porter notes that bronze-based white Hollands have brown eyes while black based birds have blue eyes. I do not know if this holds true for all strains of white turkeys.

The white site is more interesting than this, though. It is also the site of the gray gene, cg. So a bird will some combination of two of C, c, or cg. Oregon grays, which are a beautiful collection of shades of gray, are b+b+cgcg. Interestingly, the black-wing based version of Oregon gray, b1b1cgcg, is a sweetgrass. Sweetgrass turkeys look more red than gray, but do not have any red genes. They are often confused with calicos, that do have a red gene.

The cg gene is also called the palm gene. Royal palms are black-wing based with two palm genes and two Narragansett genes, b1b1cgcgngng. The royal palm is the basic uncolored palm. All other palms are based on the b1b1cgcgngng, and just add other genes for color. For example, Calicos add one red gene b1b1cgcgngngRr. Red palms have two red genes, b1b1cgcgngngrr. Similarly blue palms add blue genes and chocolate palms add brown genes.

 

[Lagerdogger]

Lesson 6: Application – Making one color turkey from two other colors

If you’re not familiar with genetics, you might want to read this one slowly.

This was originally written with Narragansetts and Bourbon Reds, but the sex-linking made it complicated. Replaced the Narris with Oregon Grays. I hope I fixed it in all the right places.

Let’s pretend that the only heritage breeds left are Bourbon Red and Oregon Gray. But you want to have standard bronze turkeys that always breed true. How do you do this?
Let’s assume you have enough reds and grays so we don’t have any problems with inbreeding, and you can select for nice shape, size, and all those other things that we’re not talking about, so that all we have to worry about is color gene combinations.

What are we starting with. The Bourbon Reds are b+b+rr. Many other color genes that are turned off are not listed. The Oregon Grays are b+b+cgcg.

If we cross the two, all of the offspring will be b+b+CcgRr, because all the poults get b+Cr from the bourbon red parents and b+cgR from the gray parents.

Now we will pick out some toms and hens from this cohort, and breed them to each other. All the offspring will be double bronze-based b+b+. But the toms will contribute either an Cg or a cg at the gray site. Listing the father’s contribution first, we will have equal numbers of CC, Ccg, cgC, and cgcg. This can be rewritten with dominant gene first as

25% CC, 50% Ccg, and 25% cgcg

Each parent also has an equal chance of contributing an R or an r at the red site resulting in

25% RR, 50% Rr, and 25% rr.

Since the inheritance of the gray genes and red genes are independent of each other, the chance of getting any combination of gray genes and any combination of red genes in the same poult is just the product of the probabilities. So the likelihood of a poult being CCRR is 0.25*0.25, or about 6% The chance of being CcgRr is 0.5*0.5 = 25%
All the possible genetic combinations, and corresponding colors are

b+b+CCRR 6.25% Standard bronze
b+b+CCRr 12.5% Red Bronze
b+b+CCrr 6.25% Bourbon Red
b+b+CcgRR 12.5% Standard bronze with recessive cg
b+b+CcgRr 25% Red Bronze with recessive cg
b+b+Ccgrr 12.5% Bourbon red with recessive cg
b+b+cgcgRR 6.25% Oregon Gray
b+b+cgcgRr 12.5% Some kind of tri-color?
b+b+cgcgrr 6.25% Something buffy?

Since we are trying to produce a strain of true breeding bronzes, we would eat all the birds that were Oregon Gray or had obvious red genes, and keep only the birds that looked like standard bronzes.

Some of these birds would be standard bronze b+b+CCRR, but some would also be carrying a single cg gene but still look like standard bronze b+b+CcgRR. How do we tell which toms carry the unwanted gene?

This is where good record keeping comes into play. By breeding different toms to hens in a systematic manner, three things could happen. You could breed true St. Bronze to St. Bronze, and all the offspring look like St. Bronze. You could breed a St. Bronze to a bird carrying a cg gene, and all the poults would still look like St. Bronze, or you could breed to birds carrying the cg gene, and some of their poults will be Oregon Gray. Whenever you find a pair of birds that produced gray birds, they and all their offspring with any other birds are culled. Eventually, the cg genes will be eliminated. This may take quite a while.

 

[HallFamilyFarm]

Quote:
Kevin is about the best out there in the field of turkey genetics.

Lagerdogger, where did you learn most of your turkey genetics? Just curious.