Let's start with the most obvious and prevalent gene in this sex chromosome, the gene for color. As most of you know there are only three basic colors found in pigeons, those being ash red, blue/black, and brown. The term blue/black is used to simplify the fact that this is the same color, blue just appearing to look different because of the way the color pigments are arranged. Any other colors that you might be familiar with are not included here because they are created by mutations or modifiers to one of the three basic colors. The original rock pigeon is reported to have been a blue bar pigeon, so the color blue/black is referred to as "wild type", and all other colors mutated from this. Ash red is dominate to blue/black and brown is recessive to it. This order of dominance plays an important role in sex linkage. So, the sex chromosome is going to contain one of these three color genes. Another gene that can appear on the sex chromosome is Almond or Fade. These two mutations or "factors" are located on the same locus position on the chromosome, just as is for color where the three different colors are in the same locus (or location) but only one can be present. So, a chromosome can carry the factor for almond or fade, but not both. These two factors are the most dominate in order of dominance on the chromosome, with the color gene being next in line in order of dominance. The next gene locus recessive, or below, the color gene is the gene for intense. This is what makes the colors appear as we know them, that is ash red, blue or brown. However, there are two identified mutations to this gene, both recessive to it that are referred to as 2 "dilution" and "pale". The dilution gene is very common, but the pale mutation is very rare and probably has not been introduced to kings. These two color modifiers lighten up or "wash out" the intense colors. The last gene locus on the sex chromosome, and lowest on the ladder of dominance, is for non-reduced, the mutation of this being reduced. Reduced is a factor that changes the intense color to a pastel color, giving it a different appearance from the dilute or the pale.
So, let's sum this up so far. Cocks carry two sex chromosomes, hens carry one. Each sex chromosome has four distinct locations (locus) arranged like a ladder in order of dominance, with these locus positions containing genes that affect the color and appearance of the pigeon. Starting with the most dominate, these genes consist of:
1. Almond, fade, non-almond or non-fade.
2. Ash red, blue/black or brown.
3. Intense, dilute, or pale.
4. Reduced, or non-reduced
A single sex chromosome can contain any combination of these genes or modifiers. So, you could have an ash red hen that would only utilize the number two loci, making her ash red, period ! Or she could carry the dilute gene from locus three which would make her a dilute ash red (ash yellow). Never seen, but a possibility could be a ash yellow almond, or a pale blue fade. How about a reduced dilute brown almond ? well, kind of far fetched and not seen in our show kings, but you should get the picture. Any of these combinations are possible if these factors are introduced into the king pigeon.
Now, let's get to sex linkage. Understanding what genes can be contained in a sex chromosome will allow you to make matings which can determine the sex of the offspring. As previously stated, cocks have two X chromosomes and hens have one. From what we just learned, these chromosomes can contain many different combinations of genes or "factors". Each of the two chromosomes the cock carries can be different in makeup, so this allows for even more input. In the process of mating, the cock pigeon contributes one of his two chromosomes and the hen may or may not contribute hers. If the hen does not pass down or contribute her genes contained in her sex chromosome, then the squab that hatches will only have one which it got from the cock, making the squab a hen. But if the hen does contribute her X chromosome in this process, then the squab that hatches will have two and it will be a cock bird.
OK, so what makes a sex linked mating ? Well, if we know the genetic makeup of a mated pair, then we can determine some things before we even get an egg laid. Let us use some examples, starting with the most common. We mate an ash red hen to a homozygous blue bar cock (homozygous means that both his X chromosomes carry the color gene for blue/black). If the cock contributes one blue chromosome and the hen does not contribute to the egg, then the baby will be a hen and will be blue. All hens produced from this mating will be blue ! However, for the next egg the hen does contribute her sex chromosome, containing the color gene for ash red. The cock will also supply his blue gene to the egg, so the baby that hatches will have two sex chromosomes, making him a cock bird. His genetic makeup will consist of ash red and blue and because ash red is dominate to blue, the blue will be hidden and the bird will be ash red in color ! All cocks raised from this mating will be ash red. This is a classic example of sex linked mating, all blues raised will be hens and all cocks raised will be ash red. Now, these cocks raised from this mating will carry blue and ash red, one color on each sex chromosome, so they will be considered heterozygous, not homozygous as in the father. An ash red cock mated to a blue bar hen is not a sex linked mating. To establish a sex linked mating, the hen must always be dominate in any of the colors or factors that are contained on the sex chromosome.
Examples:
Blue is always dominate to brown - a blue hen on a brown cock is sex linked and will produce blue cocks and brown hens.
Ash red is dominate to blue and brown - an ash red hen to a blue or brown cock is sex linked.
Intense is dominate to dilution - a dilute cock (ash yellow, true silver, dun, khaki) to an intense hen (ash red, blue/black, brown) is sex linked. All cocks will be intense and all hens will be dilute.
Intense is dominate to reduced - a reduced cock to an intense hen is sex linked, all cocks will be intense, all hens reduced.
Almond and fade are dominate to all of the above - an almond or faded hen on any of the above will produce almond or fade cocks and non-faded or non-faded hens.
There are also other classic examples, too numerous to list here. A mating can be sex linked for color or sex linked for other factors. Example: A faded blue hen mated to an ash red cock is not a sex linked mating for color because the hen is not dominate to the cock in color. It is, however, a sex linked mating for the fading factor. The faded hen is dominate to the non-faded cock, so all cocks from this mating will be faded and all hens non-faded. The color of these offspring will vary depending on the genetic makeup of the cock. Another example: An ash yellow cock mated to a blue bar hen. Not a sex linked mating for color, but it is for dilution because the dilute cock is recessive to the non-dilute hen. All hens raised from this mating will be diluted and all cocks intense in color.
Well, enough is enough ! I will hit on some forms of sex linked matings in future articles, but this should help you understand the sex chromosome and its role in sex linked matings. Remember, there are many other chromosomes in the pigeons makeup, chromosomes that determine eye color, pattern, spread, grizzle, indigo, etc. but these genes are not located on the sex chromosome so they do not play a role in determining the sex of a pigeon. More on these factors later. Good luck in breeding the best possible king you can, a knowledge of some basic genetics will surely help !
