As canary breeders, our goal is to selectively breed offspring with desirable genetic traits while excluding undesirable ones. In this article, I aim to provide a clear and concise explanation of the essential terms in canary genetics and inheritance laws. By understanding these concepts, you will be able to predict the colors of canary offspring and make informed breeding decisions. I will avoid unnecessary scientific jargon, as our focus is on practical application rather than theoretical understanding. Let’s begin by defining a few key terms.
Difference between Chromosomes, Genes, and DNA
There is a close connection between chromosomes, genes, and DNA to the extent that they are, sometimes, used interchangeably. But they are not the same thing. The cell embraces chromosomes inside its nucleus. Chromosomes are the structure that contains thousands of genes, and genes are made up of deoxyribonucleic acid (DNA).
Humans have 23 pairs of chromosomes. Only one pair is a sex chromosome, which determines the sex of offspring – male or female. The rest are autosomal chromosomes or autosomes. To differentiate between sex and autosomal chromosomes, we use letters (X and Y for example) for the former and numbers for the latter. I will explain the difference between these chromosomes in the next section.
As far as birds are concerned, they contain a different number of chromosomes, and the number depends on the species of bird, and we do not care much about the correct number of chromosomes for canaries or other birds. We only need to know that birds, like humans, have one pair of sex chromosomes, and the rest are autosomes. Chromosomes come in pairs because the offspring inherit one chromosome from the father and one from the mother.
Difference between Autosomal and Sex Chromosomes
The sex chromosomes are responsible for determining the sex of an individual, male or female. In humans, if the baby is a male, it carries the XY chromosomes, while the female carries the XX chromosomes. All traits that interest us as breeders are found on the X chromosome, not the Y. Any trait found on the sex chromosome is sex-linked, and it, therefore, passes from parents to male offspring only or female offspring only. On the contrary, traits located on autosomal chromosomes are not sex-linked, and thus, they pass to both males and females with an equal possibility.
Here we need to talk briefly about how pregnancy occurs in humans. The sperm penetrates the egg, and here fertilization or pregnancy occurs. The sperm cell carries 23 chromosomes, and the egg cell contains the same number. The female (egg) could only have an X on the sex chromosome. But the male (sperm) could either have X or Y. So, the egg has no choice but to give X to the offspring, while the sperm has two options, either to give X or Y.
The female always carries XX, so the male is the one who determines sex. If the sperm cell bears Y, then Y from the male combines with X from the female, and thus the baby is a male. But if the sperm cell carries X, then X from the male combines with X from the female, and hence the baby becomes a female.
The same applies to birds, except that the total number of chromosomes is not the same as I mentioned earlier. Most importantly, the female determines the sex, not the male, so the female carries XY and the male XX, and instead of using the X and Y system for the sex chromosomes, we use the Z and W system for birds, but I will keep using the human system for now.
The Y chromosome is relatively smaller than the X chromosome, which means that it carries a much smaller number of genes. Consequently, most genetic traits of interest to breeders, including color mutations like brown color in canaries, are located on the X chromosome.
To determine if a mutation is sex-linked or autosomal is to observe whether the mutation is inherited differently in males and females. If the mutation is only expressed in one sex (e.g., only in males or only in females), then it is likely sex-linked. If the mutation is expressed in both sexes, then it is likely autosomal.
We shall see why this information is useful when discussing traits or mutations that are sex-linked in the upcoming sections.
Mutations and Genetic traits
Since we know by now what DNA is, we can define a genetic mutation. It is simply a permanent change in the DNA sequence. When a gene mutates, the offspring may possess a genetic trait that is different from their parents. There are several types of mutations, some of which are inherited and others are not. What concerns us is heritable mutations. For this reason, all mutations mentioned in this article and the upcoming ones are inherited from parents to offspring. Before I list the most common mutated canary colors, you need to understand the difference between melanin and lipochrome pigments explained in our articles “Canary Types and Varieties” and “Types and Varieties of Canary Colors“.
Mutations for color-bred canaries include:
- Yellow lipochrome (yellow canary)
- Ivory lipochrome (diluted yellow canary)
- Red factor (Red ground color but when fed red and orange pigments)
- Red Ivory (diluted red lipochrome)
- Dominant white (white canary with yellow tints on the tip of its wings)
- Recessive white (purely white canary)
- Brown or cinnamon (ground yellow lipochrome and brown melanin)
- Fawn (ground white color and brown melanin)
- Blue (White ground color and black/brown melanin)
- Agate (Extra diluted black melanin)
- Isabel (diluted brown melanin)
- Onyx (white ground color and dark black melanin)
- Albino (White ground color canary with red eyes)
Note, color canaries can have a combination of these mutations for example the blue opal canary.
Other mutations that canaries inherit which are not related to feather colors include:
- Intensive feathers autosomal dominant
- Frosted feathers autosomal recessive
- Crest autosomal dominant
Difference between Genotype and Phenotype
The phenotype is simply the genetic trait that physically appears on the bird’s body, such as the color of the feathers, while the genotype is the genetic information that may have allowed a specific trait to appear on the bird or disappear from the bird. The genotype generally contains two alleles, one inherited from the father and one from the mother.
Remember when I said that the nucleus inside the cell carries a genetic copy from the father’s chromosomes and another copy from the mother’s chromosomes and that a chromosome is a structure that contains genes inside it, and that DNA is made up of lines of these genes?
Now imagine that the DNA contains genetic information or instructions for the green color. What is the genotype for this trait? If the father is pure green, he will carry two genetic copies (alleles), let’s call them GG (twice because the father inherits a green copy from his mother and another green copy from his father), and if the mother is also pure green, she will carry the same copy as well, so the chick will inherit a copy from his father and a copy from his mother, so he becomes pure green as well. So the genotype of the offspring is GG, and the phenotype is green.
Note, There is no canary with green feathers, the green color is just an optical illusion, as the ground color is yellow covered with black or brown and black melanin, and thus the bird appears to the naked eye green.
Heterozygous and Homozygous and Dominant vs. Recessive
In the previous example, the male and female were carrying identical genetic copies or alleles GG (pure trait), but sometimes the male and female can carry two non-identical copies such as Gb (mixed trait), G for green, and b for brown as an example. Will the chicks be green, brown, or brown and green in this case? The answer depends on several things: Does the male or female have a homozygous allele or two identical versions of the gene (GG) or heterozygous, which means two different copies of the gene Gb?
The answer also depends on the genetic trait. Is it dominant or recessive? Here, we have two traits: brown and green. Is green dominant over brown? Meaning does the green color overcome the brown color and appear on the chick and suppress the brown, or is the brown color that will overcome the green, and thus appear on the chick? And Is the genetic trait linked to sex or not?
Let’s say we want to cross a green male canary with a brown female canary and also assume that both colors are not sex-linked and green is dominant over brown.
- Both the green male and brown female are homozygous for their respective color alleles
- The genotype of the male would be GG (two dominant green alleles) and that of the female would be bb (two recessive brown alleles).
Following the principle that green is dominant over brown (represented by capital G and lowercase b, respectively), we can predict the possible outcomes for their offspring as follow:
- All offspring will be green and carry one copy of the brown allele (Gb).
- None of the offspring will be brown as they need to inherit two copies of the brown allele to express the brown trait.
- The probability of each offspring being green and carrying one copy of the brown allele (Gb) is 100%.
If we assume that the female is green (GG) and the male is brown (bb) and both green and brown are not sex-linked, the predicted outcome of their offspring would still be the same as before.
Now let’s assume the male is dominant green and female is recessive brown and brown is sex-linked while green is not, the result would be:
- 50% green males
- 50% green females
The following chart will help you determine whether the mutation you are dealing with is sex-linked or autosome and whether it is dominant or recessive:
So based on the principles of genetics and the information presented in the table, we can make predictions about the possible outcomes of offspring when we breed canaries with different mutations and traits.
Canary Offspring Sex Determination through Genetics and Inheritance Laws
Determining the sex of canaries involves looking for sex-linked mutations that are associated with certain physical traits, such as feather color.
In canaries, there are sex-linked mutations that affect the color of the feathers. For example, the brown mutation is a sex-linked recessive trait that is located on the X chromosome. Male canaries that carry one copy of the brown mutation will have brown feathers, while females must inherit two copies of the mutation (one from each parent) to have brown feathers.
By observing the feather color of the offspring, a breeder can determine the sex of the bird based on whether or not it has brown feathers. Offspring with brown feathers must be female, as they inherited two copies of the brown mutation, while offspring with non-brown feathers can be either male or female, depending on their genetic makeup.
It is important to note that this method only works for sex-linked mutations that are associated with visible physical traits, and it is not always 100% accurate. Genetic analysis is generally considered a more reliable method for determining the sex of canaries.
Written and authored by Omar Abusalem Edited and Co-authored by Bashar Jarayseh