Budgerigar Genetics

by the late John Walkley

There is an old proverb that says "Like begats like."" Although there may be some variations in likeness, we would be surprised if an offspring did not resemble its parent in some way. For instance, we would be astounded to find a budgie chick which had the shape or the song of a canary or finch (well, most of us would!). To understand why this doesn't occur, and why likeness in shape, size and colour, and the countless other characteristics, are carried from generation to generation, we need an appreciation of the principles and mechanics of heredity.

In this article, we'll look very briefly at the history, early work and terminology of genetics, with the idea of cross-referencing them to the genetics of the budgerigar. Of more direct interest, we'll have examples of colour genetics and line/inbreeding.

Hopefully, this will give some knowledge of genetics on a broad front, without going into too much complex detail (and genetics can be complex). All, of of course, with special reference to the budgerigar.

History of Genetics

Heredity is a phenomenon familiar to everyone nowadays. However, it has not always been accepted as such. In Greek mythology, human beings arose from animals, trees or stone, and could easily be turned back into these. Indeed, the Greek philosopher, Aristotle (384-322 BC) believed that plants and lower animals, such as snails and flies etc., spontaneously arose from decaying matter. This may possibly be explained by the appearance of flies etc., around piles of decaying leaves.

It wasn't until the work of Louis Pasteur (1822-1875) that this notion was finally laid to rest. Pasteur showed that the spark of life could only be kindled by life itself. This is applicable to all life forms, including the most minute organisms such as bacteria and viruses.

About this time, many scientists were trying to solve the mechanism of inheritance. One line of thought was that heredity was transmitted as though it were a fluid, like blood. In this manner, parents transferred some of their fluid to the offspring, which consequently showed some of the parents' characteristics. Although this theory has been disproved - blood has absolutely nothing to do with the transmission of heredity, the terms "pure-blooded", "half-blooded", "blood-line", etc., still remain in use.

The first person to provide a theory and convincing proof was Gregor Mendel (1822-1884), a monk in an Augustinian Abbey in Austria. Mendel had studied natural science, and whilst at the monastery, he undertook a study of the characteristics of the common garden pea. At the end of it in 1885, Mendel published a paper of his findings, and the generalizations we now know as "quot;Mendal Laws".quot; His paper, which explained heredity by the transmission of units called genes, lay neglected for years, until his death. It was then rediscovered by three scientists who had each independently obtained results confirming Mendel's work. The importance of the work was quickly realized and many other scientists carried out all sorts of experiments with animals and plants to show that they all followed the same manner of inheritances that Mendal had predicted. This is a convenient spot to look at some of the terms that Mendal used.

Terminology of Genetics

Genes

From his results, Mendal was able to conclude that contrasting characteristics were determined by "something" that was transmitted from parent to offspring (via the sex cells). This "something" he called genes. Simply, genes are found in the cells of the body, or more exactly, on tiny bodies called chromosomes, which are located in the nucleus of each cell. To get an idea of their minuteness, consider that the human body contains some 200 billion or more cells. The budgerigar probably consists of about a billion cells. But how do we describe genetical make-up?

Genotype: Literally, the genetic description of an individual.
Phenotype: The external or physical appearance of the individual.

These two terms are easily remembered by the first few letters, eg:

Genotype=Gen=Genetic (Description)
Phenotype=Ph=Physical (Description)

The phenotype of a light green budgerigar would obviously be light green. However, its genotype may, or may not, be the same as the phenotype. It could be a pure light green, or light green "split" (masking) blue or dilute, etc.

Homozygous

To understand this term one needs to realize that chromosomes come, one from each parent and are hence genes, and arranged in pairs. Each pair of genes is responsible for a particular characteristic and may consist of two dominant genes, two recessive genes or one of each. Where the two genes are similar (whether dominant or recessive), the individual is described as homozygous, or true breeding, for a particular characteristic.

Heterozygous

Where the pair consists of one dominant and one recessive gene, the individual is heterozygous, or a hybrid, for the particular characteristic.

Editor's Note: This article is part of a booklet Welcome to Caring For and Breeding Clearwing Budgerigars used as a welcome to new members of the CBBA and is reprinted by kind permission of that Association.

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