Abstract
I NTRODUCTION
It is not unusual for beginner and novice parrot and cockatiel breeders to misunderstand the topic of linebreeding and inbreeding. Often times I'm asked, What is the closest a cockatiel could be related to another cockatiel without producing genetic defects or lethal factors?
INBREEDING
To answer that question we must trst de Che inbreeding. Among the stricter proponents, inbreeding includes pairings such as parent to offspring, siblingto-sibling, and half-sibling to half-sibling. A less strict detriition contnes inbreeding to brother-sister pairings only. This article will refer to inbreeding as the breeding of brother to sister pairings.
Some readers may be surprised to learn that the closest genetic breeding is to mate brother to sister. Genetically, brother to sister pairings are the most identical to one another, closer even than to their own parents. Because each sibling inherits half its biological genome (all its genes) from its sire, and the other half from its dam, each chick shares nearly the same identical genes as its siblings.
By comparison, a son paired to its own mother would share only half its genes with its dam; similarly, a daughter paired to its own father would share only half its genes with its sire. Because full siblings carry genes from both their parents, brothers and sisters would share the greatest number of genes in common.
Now, with that being said, it is best understood that most hobbyists should never breed brother to sister pairings, most of the time, in the majority of circumstances. Although special conditions do exist where inbreeding may be permitted, they are better intended for the advanced champion breeder and never for the inexperienced to experiment with.
Unfortunately, it is often the beginner or novice breeder who unwittingly or unknowingly dabbles the most in inbreeding! For example, siblings bred from one pair may take advantage of breeding with one another; or, the hobbyist may allow full or half siblings to breed, not fully understanding the dangers and consequences of such unions.
Inbreeding should only be undertaken in a wellestablished linebreeding program where the aviculturist has many years - often more than a decade - of background knowledge and experience or fully understands exactly what is to be accomplished by the union. Ideally, a planned inbreeding trial is carried out with the express purpose of introducing a new characteristic into an existing, established line. The goal of the inbreeding trial is to set an identitable characteristic (e.g., a new color or superior show trait) into a line in order to create a new strain, embedding this characteristic within an already developed aviary stud.
However, in inbreeding practices, not only will all the superior, (positive), recessive traits rise to the surface; inbreeding will also force all the inferior, (bad), recessive traits to the surface. By trait, I am referring to any inherited gene for color, shape, size, personality, fertility, parenting skills, immune system, health, or any other visible or invisible characteristic. There are countless traits that are inherited through the genes of an individual bird. Although this process also applies to linebreeding, it is even more intense in inbreeding practices.
So why breed brother to sister? Brother to sister matings can be attempted under very special circumstances such as setting a particular trait into proven, pedigreed champion or grand champion stock where the seasoned aviculturist fully understands the beneQs and risks taken. However, serious culling of the stock is necessary, usually by selling off as pets any undesirable birds produced.
In informed inbreeding practices among seasoned breeders - contrary to horror stories - not all young produced are hideous, monster chicks! Unfortunately, frightening stories about inbreeding among humans, or inappropriate pairs of animals that are not suitable candidates are what abound. The taboo is necessary among humans, but not among all animal pairings. Livestock husbandry is based upon linebreeding and occasional inbreeding practices.
In fact, if superior champion birds are used it is possible to produce a highly valued trait. However, simply pairing a brother-sister combination merely because they are champion stockmoes not guarantee this result! One must know precisely what the goal of a union is and which trait is sought.
There can also be special exceptions necessitating inbreeding such as when there are no other relatives available, or when attempting to quickly prove a
new color mutation. However, even then it would be safer, and more preferable, to breed back to a parent because parent and offspring share only half the genes as compared to full siblings.