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Basics of Genetics

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Genetics is a vast subject, so here I can only give a few the basics of genetics and how it relates to budgies and their breeding.

The shape, size, and color of every budgie is controlled by its genes. There are thousands of different genes, each controlling some little detail. Budgie breeders are usually most concerned with the ones that control color, so those are the only ones that will be dealt with here.

For each gene, there are two copies. These may be the same as each other, or they may be different. When a pair breeds, each parent gives each offspring one of each gene at random. Since there are two copies of each gene, that means that one copy is inherited from the mother and the other from the father.

Genes can behave in lots of different ways, but the most important are dominant and recessive. For dominant genes, a budgie only needs one copy to show the trait it controls. For recessive genes, it needs two copies, one from each parent. If a budgie only has one copy of a recessive, then it won't show the trait, but it can still pass the gene to its offspring. This situation is called a split.

For example, the most basic color controlled by genes is green/blue. Green is dominant and blue is recessive. Blue budgies always have two copies of the blue gene because it's recessive. Green budgies might have two green genes, but since green is dominant, they might also have one green gene and one blue gene. This is called "split to blue." A split doesn't show the trait that it is split to. It's hidden. You can only know you have a split before you breed a bird by knowing what its parents are.

If a budgie has two copies of the same gene (for example, blue-blue or green-green), then you know that gene will be passed to its offspring. If its two copies are different (for example, blue-green) then each copy has a 50% chance of being passed on to each offspring.

If you breed two blue budgies, then all their offspring will be blue. This is because both parents can only pass along blue genes, not green ones. If you breed two green budgies that are not split to blue, then all their offspring will be green, and will also not be split to blue. This is because both parents can only pass along green genes.

If you breed a blue budgie and a green budgie that is not split to blue, then all the offspring will be green, split to blue. This is because they got a green gene from one parent and a blue gene from the other.

It gets more complicated when you breed splits. If you breed a green split and a green that is not split, you will get all green offspring, but half will be split to blue! This is because the non-split parent will give them all green, but the split parent will give half green and half blue. If you breed a green split and a blue, then you will have half green split and half blue. This is because the blue parent will give them all blue, but the split parent will give half green and half blue.

It's most complicated when you breed two splits! This match will produce 25% green non-splits, 50% green splits, and 25% blue!

That's how all dominant and recessive genes usually work. Remember, dominant means only one copy of the gene is needed to show a trait, and recessive means two copies are needed.

A major exception to the dominant/recessive rules is sex-linked genes. Sex-linked genes are even more confusing! Budgies have special sets of genes called chromosomes that tell what sex it is. In budgies, XX means male, and XY means female. (See the note on humans at the bottom.) The little Y chromosome is so small that it carries almost no genes at all, so it can be ignored. This means that while males have two copies of every sex-linked genes, females have only one! Because of this, females cannot be split for sex-linked genes. If she has a dominant sex-linked gene, it will show as dominant, and if she shows recessive, it will show as recessive, even though she has only one copy of the recessive. Splits work the normal way for males' sex-linked genes.

If you're not confused yet, then here's an example! It uses and albino/lutino-normal (I'll call this one ino-normal). A blue budgie showing the ino gene will be albino (white with red eyes), and a green budgie showing the same ino gene will be lutino (yellow with red eyes). Ino is sex-linked, and it's recessive. Normal is dominant.

If you have a male ino, then it must have two copies of the ino gene, because ino is recessive. But if you have a female ino, then it has only one ino gene, because females are the exception: they only need one recessive if it's sex-linked. Females only have one copy of any sex-linked gene.

If you breed an ino male and an ino female, then all of the offspring will be ino. Likewise, if you breed a normal male who is not split to a normal female, then none of the offspring will be ino. (Remember that females cannot be split for ino.)

If you breed an ino male with a normal female, then half the offspring will be normal males split to ino, and the other half will be ino females. This is because the father gives ino to all his offspring, while the mother gives normal genes to all her sons, but none of these genes to any of her daughters. (Remeber the daughters only have one copy of these genes too!)

If you do the opposite and breed a normal (non-split) male with an ino female, then all of the offspring will be normal, since they all get a normal gene from their father. The males will all be split to ino because their mother gave them the ino gene.

Now the most complicated part: the split male. If you breed an normal male split to ino and an ino female, you will get 25% normal males split to ino, 25% ino males, 25% normal females, and 25% ino females. If you breed a normal male split to ino and a normal female, you will get 25% normal non-split males, 25% normal split males, 25% normal females, and 25% ino females. If you want, you can figure out the math.

That's the basics of how genes are passed from parent to offspring. Nobody said it would be simple! It's like a puzzle. If you understand and enjoy the puzzle, and if you love birds enough to devote the money necessary, then perhaps you would make a good budgie breeder!

NOTE FROM ABOVE: Humans are just the opposite of budgies. XX means female, and XY means male. So sex-linked genes in humans work the opposite of the way they work in budgies.

Thanks to John Machado, Maddy, and everyone on Budgie Chat for the knowledge they contributed to this page.

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