The Wonders of Genetics, Sex Linkage, and Feather Colors.

The science of genetics, indeed, deals in wondrous happenings and that's most certainly true with Budgerigars. It's nothing short of miraculous that the original green Budgie gave rise to more than 50 different color variants. The miracle is on a different level that the way the "street-wise' breeder sees it. The miracle is not random. It is neatly predictable with just a few exceptions wrought by Mother Nature. The facts add up well, and they are simple enough for a person with ordinary intelligence to grasp and use. After a short rime, they seem easy to work with. True, a bit of patience and perseverance is needed. Take out sheet of paper and note unfamiliar scientific words you'll need to understand. Write down the meanings and study the implications. Soon theories will lead to practical benefits in your hobby. You can take your new knowledge quite far and achieve your " miracles" rather quickly with minimal expense. Genetics provides you with the peace of mind that nothing will happen to throw a monkey wrench into your breeding plans. It also provides you with insurance that you won't chase after unattainable goals. And you'll know what you need to achieve the goals that you can attain.

For example, if you want to breed a violet variant, you will know that you don't have to buy more than a single violet bird. When a new variant comes into vogue, you will be able to meet the demand while the price is high. And you can graduate to the highest level of Budgie breeding the development of an entirely new color variant. No one can say that the breeding programs that led to 50 new color variants have to stop there. You can be the person of the future who will add something new and desirable to the Budgerigar.

Building Blocks of the Body
Every form of higher life derives from the merger of an egg cell contributed by the mother and a sperm cell from the father. This merger forms a new cell called a zygote. After a period of development, this zygote forms a new living being. To put this into avian terms, when a female and a male Budgie mate, the egg cell of the female is fertilised by the sperm of the male. These two cells meld into one, out of which the Budgie embryo grows. If the egg housing the embryo is properly brooded, it develops into a young Budgie. The body of man, beast, bird, or plant is made up of millions of cells, all of which are derived from the one starter cell by means of cell division. At a certain moment, a wall is formed within the starter cell and soon the cell splits in two. In this way, one cell gives rise to two; two cells develop into four, four cells become eight and so on, till after seven more divisions we have 1,024 cells. Cell division can be quite rapid once it gets underway.

Cell division, then, is the method by which an egg develops. The zygote (or starter cell) forms the egg yolk, which comes into the world surrounded by a layer off egg white and another protective layer off egg shell. And there it lies in the nest of your Budgies, ready to be brooded until 20 days later a young is hatched. Cell division keeps progressing after hatch until a full-grown Budgerigar has been formed. To understand the process, lets return out attention to the original egg cell and sperm cell, which also are called gametes or reproductive cells. The reproductive cells contain everything that contributes to the development of a new bird. Once the gametes meld, they give rise to a new body, to feathers and legs, to wings and eyes, and to color traits and behaviour.

More information on GENETICS can be found at Budgerigars Galore by Dolores Noonan.

The whole miracle of reproduction occurs inside the melded new zygote The carriers of life operate in that small space to organise the construction of the new bird to be. These carriers of life are called chromosomes. As I just mentioned, the zygote successively forms into two, four, eight sixteen cells and so on. If this process were to go too far, we would get a Budgie of gigantic dimensions. There has to be a mechanism that regulates growth, that says at a given moment: "Stop! Development is complete. We now must start into maintenance." This mechanism is provided by the chromosomes. You can see them under high magnification in a microscope as small clumps inside the cell. Inside the chromosomes are housed still smaller bodies, called genes.

These genes determine the genetic traits of the developing Budgie. They determine the color and every other detail about the new Budgie. For the breeder, they do the most important of jobs. Each body cell contains a certain number of chromosomes, always in even numbers. When a cell divides, the chromosomes also divide. Therefore the new cell contains the same number of chromosomes as the original cell. If the original cell starts with eight chromosomes, then cell division results in two cells, each also containing eight chromosomes. Normal cells always have the same number of chromosomes. No matter how many times they divide, each daughter cell maintains the eight chromosomes.

The Exception: Reproductive Cells
Reproductive cells represent an exception to the basic rule of cell division. The egg cell and the sperm cell described above contain just half the usual number of chromosomes. For example, body cells of Budgerigars normally contain 14 chromosomes. But the egg cell of the female contains only seven; so does the sperm cell of the male. Once these two reproductive cells meld into the zygote, the female contributes seven chromosomes and the male contributes another seven. Together, they once again provide 14 chromosomes. As the zygote with its 14 chromosomes starts dividing, normal cell division occurs once again. And again, every daughter cell gets 14 chromosomes, derived from the original zygote.

Why does this happen? Nature never does anything without a reason. If the egg cell and the sperm cell would contain the normal number of Budgie chromosomes(l4), then after mating we would get a melded cell with 14 plus 14 chromosomes---a total of 28. If that cell were to divide in the normal manner, we would get cells that all contain 28 chromosomes, giving rise to a Budgie with body cells of 28 chromosomes. But a Budgie by nature has just 14 chromosomes per cell. So we would get a bird that would not have the proper number of chromosomes to be a Budgie! Such reflections are, however, academic. By the dictates of hereditary the egg cell and the sperm cell must have one-half the number of chromosomes of ordinary cells---half from the male parent and half from the female parent. Because chromosomes are the carriers of the various hereditary traits transmitted by the genes, the bird inherits traits from both parents according to their own genetic make-up.

Single and Double factor
Single factor means the baby got one factor such as spangle from either the male or the female parent.
Example: If you bred a normal with a spangle you would get 50% normal babies and 50% spangle babies. The spangle babies would have picked up the spangle factor from just one of the parents so it is noted as having a single factor in its background.

Double factor means the baby got one factor such as spangle from both parents.
Example: If you bred a spangle to a spangle you would get some spangle babies having the spangle factor from one of the parents, making it a single factor spangle, and some babies with the spangle factor from both parents making it a double factor spangle. There would also be some normal babies carrying none of the factors or no genes for spangle.

Other samples of factors are cobalts dark factor, mauve etc. A factor is sort of like a color or modifier and not a variety such as Cinnamon or Opaline.

No Water-colour Set
If the parent birds are white and green, the young inherit both white and green color genes. So they should look more or less half green and half white, or some color in between. But Nature doesn't work like a water-colour set that makes up light green by mixing white and green together. There are more elements that influence heredity. You see, there are visible and invisible genetic factors called recessive and dominant. If you dislike strange words, you can call them shy factors and aggressive factors. For the heredity of Budgies, these are of prime importance in most cases, one color factor appears to dominate the other. For example, a green Budgie can be "white" at the same time, even though it doesn't look white. Its whiteness is overpowered by its greenness, or in other words, green coloration dominates over white, so that people speak of dominant green. The bird being described is obviously green, but has received the white gene also from one of its parents even though it isn't visible. The white color therefore is called recessive---or shy if you like. To repeat, the zygote receives the genes of both the male and the female. It thus contains a gene for white, and therefore the developing young will carry this gene in all its cells. But you can't tell that from the young birds appearance.

Homozygous Versus Heterozygous
A bird that carries a second, hidden color trait in addition to its apparent color is called a heterozygote. That's a difficult term. A good translation of that word would be: inheriting impurely. A bird without hidden color traits is called a homozygote, which could be translated as inheriting purely. If you have understood the previous discussions clearly, you now know that a heterozygous bird and a homozygous bird can look exactly alike. A homozygous (or purely inheriting) green bird is completely green in its makeup, while a heterozygous green bird can look just as green, but carries a hidden, invisible trait for another color. Two homozygous green Budgerigars will always produce homozygous green young, for the simple reason that no Budgie, in fact no organism, can give its young a trait that it doesn't carry itself. Let's look at a Practical example.

John Williams, the barber, wants to start breeding Budgies. One of his clients told him that Budgies are truly pleasant birds that are easy to breed. He has a preference for green Budgies and therefore he goes to a dealer where he blithely purchases two green Budgies. Everything goes according to plan. A few weeks later, the couple produces eggs. Another 20 days later, Williams tells his clients at the shop that he has new young Budgies. "Which color," a client asks? "Green, of course," Williams replies. "Naturally you can't see that yet," he adds. "They still don't have their feathers. But the male and the female are green, so the young will be green as well." A few weeks later, however, our friend the barber discovers that those crazy Budgies of his are not turning out to be green. At least, not all of them. Believe it or not, he has two blue ones in the brood.

Williams doesn't really mind. He can learn to like blue Budgies just the same. And maybe he thinks he has bred something quite unusual. But really, it is the most usual thing in the world. If Williams had wanted to be sure to breed only green Budgies, he would have had to ask the dealer for genetically pure green birds. If he had known the scientific term, he would have asked for "homozygous green Budgerigars." Instead he got hold of possibly two heterozygous Budgies, or one heterozygote and one homozygote. Both looked green. But one of them, or both, had a hidden trait for blue. It might not have been an easy task for Williams to purchase a pair of homozygous green birds, even if he had known about the concept and the difficult word involved. Far too many breeders work with colony breeding cages, so that they are unsure about the heritage of their birds. Only breeders who breed one pair per cage can be sure after a few seasons what type of birds they are dealing with. Only then would they be able to sell breeding birds that are genetically pure for a specific color.

And only then would their hobby be on a certain course. When geneticists speak of dark green, olive yellow, cobalt, etc., they always refer to the pure color----the color of homozygous birds. if a bird is heterozygous, they indicate this by recording the invisible color after the visible one. A green bird that also carries a white factor is called green/white. When read out loud, this is sounded as "green split for white," and the bird could be called "white blooded." Similarly, a graywing cobalt/white would be a "white blooded graywing cobalt" or a "graywing cobalt split for white. The latter designation is simple and clear. By now you understand that someone who buys a pair of Budgies without a forethought never can be sure how the young will turn out. You cannot just go by looks, because you might be encountering heterozygous or homozygous birds, or one of each. In the great majority of cases, the haphazard buyer will get heterozygotes, impurely inheriting birds, because most breeders understand too little about the theory of color inheritance. They breed shotgun style under the motto, whatever will be will be.

Serious breeders attain a good understanding of the colors lurking in their stock after a few matings. If you know what is hidden inside your birds, then you can accurately and easily predict the results of any crossing.


The sex-linked varieties are opaline, cinnamon, lutino, and albino. We will try and show the formula for Mendel's principles of inheritance. In budgerigars, it is the hen which determines the sex of the offspring. This is opposite to that of humans, where the male determines the sex.

Albinos are white and lutinos are yellow parakeets with red eyes. To put it in the simplest terms, albinos and lutinos lack the black pigment melanin altogether. This is why these birds do not even have a dark protective layer against light in their eyes, and the red blood shines through. Yellow parakeets (lutinos) are descended from the green type; white ones (albinos), from the blue type. The special thing about the inheritance of the melanin factor is that it is carried on the X chromosome and is therefore sex-linked.

Lets start first with two normal birds. Color in theses examples does not matter. They can be blue or green. The cock is shown as "X X" and the hen is "X Y" (Two "X"s will always be a cock and "X Y" will always be a hen.) In this document the small c, o, a, and l represent the cinnamon, opaline, albino, and the lutino. The important thing to remember is that hens can never be "split" for sex-linked varieties. Cocks, however, can be. What we mean by "split" is that the bird visually looks like a normal bird, (either blue or green with black and white, or black and yellow bars on the head, neck, back, and wings) but genetically he may be carrying the factor for cinnamon or opaline, etc. Or a combination of factors. When we pair up two birds, the cock will pass on one of his "X"s to the young and the hen will pass on either the "X" or the "Y". Now lets show what happens when you pair up the two normal birds.

Normal Cock "X X" and a Normal Hen "X Y" produce

"X X" normal cock
"X Y" normal hens

Quite simply, we will produce normal chicks, cocks and hens. We see this in the example above and we got the answer by taking one of the "X"s from the cock and bringing it down and then took the "X" from the hen and brought that down. As we said before, an "X X" is always a cock, so we know this pairing will produce normal cocks. Then we took an "X" ( it does not matter which one in this example, it does in other examples) from the cock and the "Y" from the hen. An "X Y" is always a hen so we will always have normal hens.

A cinnamon cock will be shown on paper as "Xc Xc". If there is a little "c" on only one of the "X"s it would split cinnamon cock. This is a cock that looks normal, but can pass on the cinnamon factor to his offspring.

A cinnamon hen is shown as "Xc Y". You will note their is one little "c" in this example. There will never be any letters attaching the "Y" only the "X" and as a hen cannot be split for any sex-linked varieties, the little "c" on the "X" in this case means she has to be cinnamon.

Now the same would apply to opaline if you replaced the word "cinnamon" in the last two paragraphs above with opaline and replaced the small letter "c" with a small "o". So an opaline cock would appear as "Xo Xo" and an opaline hen as "Xo Y".

The same also applies to lutino (L) and albino (A).

Below is a list of some of the birds and how you would show them on paper.
Remember that "X X" is the cock and "X Y" is the hen. The small "a" is albino, the small "l" is lutino, the small "o" is opaline and the small "c" is cinnamon.

X X normal cock
X Y normal hen
X Xc split cinnamon cock
Xc Xc cinnamon cock
X Xo split opaline cock
Xc Xco cinnamon split opaline cock
Xl Xl lutino cock
Xl Xlco lutino split cinnamon and opaline cock
Xo Xo opaline cock
Xco Xco cinnamon opaline cock
Xa Xa albino cock
XY normal hen
Xc Y cinnamon hen
Xo Y opaline hen
Xco Y cinnamon opaline hen
Xl Y lutino hen
Xa Y albino hen

Now using the list we will try and show some examples so you can get the idea. Remember the rule of bringing down one letter from both the cock and the hen.

Example 1
With a split cinnamon cock "X Xc" and normal hen "X Y" the possibilities are

Xc X split cinnamon cock
Xc Y cinnamon hen
X X normal cock
X Y normal hen

Example 2
With a cinnamon cock "Xc Xc" and a normal hen "X Y" the possibilities are

X Xc split cinnamon cocks
Xc Y cinnamon hens

Example 3
With a split cinnamon cock "X Xc" and a cinnamon hen "Xc Y" the possibilities are

Xc Xc cinnamon cock
Xc X split cinnamon cock
Xc Y cinnamon hen
X Y normal hens

Example 4
With a split cinnamon opaline cock "Xc Xo" and a cinnamon hen "Xc Y" the possibilities are

Xc Xc cinnamon cock
Xco X split cinnamon opaline cock
Xco Xc cinnamon split opaline cock
Xc X split cinnamon cock
Xc Y cinnamon hen
Xo Y opaline hen
Xco Y cinnamon opaline hen
X Y normal hen

The Dominent Varieties
Australian Dominent Pied-----}
Yellowface------------------- } -60% dominant approximately.

Dominant Factor Birds: To produce birds of the dominant varieties, only one of the parents has to be of a dominant type. No bird can be split dominant.

The Recessive varieties
Recessive Pied
Black-eyed Yellow
Black-eyed White

Recessive factor Birds: To produce birds of the recessive varieties, both of the parents must carry the recessive factor either in a visual form (ie a recessive pied) or in the split from (ie light green/split recessive pied.)

The SEX-Linked Varieties

Sex-Linked Birds: The sex linked factor passes from Mother to Son in the split form AND from Father to Daughter in the visual form OR to a son in the split form. (ie No hen can be split for a sex-linked factor.)

1. Opaline Cock & Opaline Hen = Opaline Cocks & Hens.
2. Oplaine Cock & Normal Hen = Split Opaline Cocks & Opaline Hens.
3. Split Opaline Cocks & Opaline Hen = Opaline Cocks & Hens, Split Opaline Cocks & Normal Hens.
4. Split Opaline Cock & Normal Hen = Normal Cocks & Hens, Split Opaline Cocks & Opaline Hens.
5. Normal Cock & Opaline Hen = Split Opaline Cocks & Normal Hens.

The sex of the offspring is controlled in this way. The hen has 2 sex chromosomes - one a male and the other a female. The cock has 2 male chromosomes. If a male chromosome from the cock meets an male chromosome from the female the youngsters will be male. If the male chromosomes from the cock meet a female chromosome from the female the youngsters will be female. Therfore, that is why the female deterrmines the sex of the babies.

It will be noted that some of the matings described above, produce normal/opaline cocks and also ordinary cocks. Generally speaking these matings should be avoided because it is not usually possible to tell from their external appearance which are split and which are non-split. This can only be proved by test matings, which entail much waste of time--possibly a whole breeding season.
Fanciers who have not studied Budgerigar genetics are sometimes confused by the terms Type I and Type II appearing against the names of birds carrying a single dark character. The following explanation makes clear the difference between the two types:- Type I are produced by crossing a Skyblue with an Olive, resulting in Dark Green/blue with the dark character from the Olive. Type II are produced by crossing Light Green with Mauve resulting in Dark Greens/blue with the dark character from the Mauve. The distribution of the shades of colour when dealing with expectations of crosses when one parent is a Dark Green/Blue Type I or a Dark Green/Blue Type II differs from the usual Mendelian percentages of each colour. The knowledge of this will help the breeder to match the breeding pairs so as to raise as many of the desired shade of colour as possible.
A Dark Green/Blue Type I of any variety paired to a Sky Blue of any variety will give the theoretical expectation of 43% Sky Blue, 7% Cobalt, 43% Dark Green/Blue Type I, and 7% Light Green/Blue. When a Dark Green/Blue Type II is used instead of a Type I then the expectation is 43% Cobalt, 7% Sky Blue, 43% Light Green/Blue, and 7% Dark Green/Blue Type II. It will be observed that both pairings however give 50% blue coloured and 50% green coloured young and it is only the shade of colour that varies. The dark character in any bird described as Type I had its origin in a bird which was Olive, and in Type II in a bird which was Mauve.

What Gives the Feathers Their Colors?

Ordinarily, objects or images look colorful to us because of their color pigment in them. But in certain objects extremely fine structures appear to our eyes as colors. A mass of tiny water- drops distributed in a certain way is a case in point; these water drops are perceived by us as a rainbow. In bird feathers both methods of producing color are at work: pigments and structural colors. A feather has a central shaft, or rachis, and vanes made up of many barbs that branch off from the shaft and interlock with barbules. The shaft provides the feather with rigidity and the vanes give it added surface for flying. The basic colors of a parakeets plumage are made up as follows:

White: The horny structure of the feather contains no pigments at all.
Yellow: The outer keratin layer contains yellow pigment; the center contains no pigments.
Blue: The keratin layer is colorless; the air bubbles in the porous zone below the keratin break light down into the rainbow colors. Dark pigments (melanin) in the center absorb all colors except blue; blue is therefore reflected.
Green: The keratin layer contains yellow pigment. The center porous zone creates blue, and yellow plus blue make green.
Black: The keratin layer and the center both contain melanin but there is no yellow pigment.

The four basic colors of parakeets, disregarding black markings, are therefore all derived from yellow and black pigments. The structural color blue appears only if black is present in the central region.

(For accuracy's sake we have to note that there are also intermediary states where black pigment is present in varying concentrations.) We have already seen that every bird has a double set of genes; the genes for yellow can therefore be in the state "F" or 'f." Consequently the trait yellow occurs in one of three possible combinations. Any given bird has inherited one of these three combinations from its parents and keeps it for life. The three possibilities are: FF-green; Ff--green, because F is dominant over f; and ff--blue. If two green parakeets are mated the outcome is quite unpredictable.

But what can you expect if your bird produced only three eggs? In this case 25% of the offspring of such matings will have genes FF, 50% will have Ff, and the remaining 25% will have ff.
(F=yellow pigment is produced.)
(f=yellow pigment is not produced.)

In actuality you are not likely to get exactly the predicted percentages. If you want results that accurately reflect the above proportions you have to breed a large number of birds.


E-Mail: berniehansen@sympatico.ca



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