Page Title

ORIGINAL
BOOK REVIEW
by
Dr. Rainer R.
Erhardt
"Well, there is help on
the horizon and
anyone seriously
interested in color
genetics should take a
look at Linda Rubin's
book: COCKATIEL
G ENETICS MADE EASY!
Though this book is
primarily directed to
breeders of cockatiel
mutations, there is
enough information in
this little volume to
teach anyone the
secrets of dealing
with recessive,
sex-linked, and
dominant mutations..."
ACBM, Vol. 65, No.12
CLICK TO READ THE
REST OF THE REVIEW!
112 pages, 15 chapters,
glossary & more!

Multiple Bird
Households
by
Linda S. Rubin

Ultimate
Parrot Guide
by
Linda S. Rubin

click for descriptions, chapter excerpts, & reviews!

Series by
Linda S. Rubin

Is the Homozygous Normal Grey Endangered?
Copyright © 2006 LINDA S. RUBIN
CF Genetics Consultant/Panel Judge
www.CockatielsPlusParrots.com
“All Rights Reserved”

Over the past several decades, breeding cockatiel color mutations
became so popular that today, finding a pure, homozygous Normal
Grey that does not carry any other color form is just about next to
impossible. Pairing Normal Grey cockatiels to other colors has been
encouraged because of the increased market demand for mutations,
resulting in Normal Grey young that are more often than not,
heterozygous or split to one, two, or a multitude of colors.

I may inadvertently be revealing my own age when I look back and
remember that I had entered the world of cockatiel culture when only
the Pied and the Lutino mutations were the only colors available at
that time. I well remember saving up for the more expensive Lutino
male I purchased prior to the formation of the two major national
societies for cockatiels in America. A few years later, I saw the
importation of the first Cinnamons and Pearls from Europe, into the
United States, with other colors to follow. We had never given it much
thought at the time whether the future would require or need pure
Normal Grey breeding stock; in truth, we were in love with the new
color varieties.

Those of us who started out by establishing breeding studs in budgies
well remember hearing about the extreme difficulty in finding a pure
Normal Green budgerigar. So many budgie breeders had used the
original Normal Green budgie in the livestock principle of "dipping into
the Green," as it was called – using pure, homozygous Normal Greens
to infuse such valuable traits as health, vitality and fertility to improve
their stock. Similarly, cockatiel breeders now fear the same fate of
losing the pure, homozygous Normal - the grey form originating in the
wild.

Yet, the question must be asked, is it important to save the original
wild form that is not split to any other color mutation? Is it necessary to
save breeding colonies of homozygous Normal Greys that carry no
other color, with the sole intent of using them to increase size, infuse
health, hybrid vigor, fertility, stamina, immunity and other valuable
traits first appearing in the wild Normal Grey, or at least in the Normal
Greys first linebred for superior traits in our early aviaries?

Today, we are fortunate to have color mutations that do carry
significant size; indeed, there are linebred color mutations that are
even larger than many Normal Greys. In actuality, size has little to do
with color; instead, size is a trait that can be controlled through the
examination of background bloodlines and the practice of selective
breeding.

Take, for example, the Whiteface mutation first imported into the
United States in 1980. As with many of the new autosomal recessive
mutations, the early birds were small in comparison to other colors.
Normal Greys and other quality linebred birds that exhibited size as a
dominant trait were chosen to improve Whiteface stock. Eventually,
with careful attention to livestock husbandry and selection practices,
breeders produced offspring in successive generations that achieved
size. As a result, today we have breeding studs with lines of quality
Whiteface, and Whiteface cross mutations, which often place over
Normal Greys in competition.

The good news is that linebreeding techniques work admirably well to
introduce size to other colors, providing the larger partners are bred
from strains that have size set into their line. Additionally, the mode of
genetic inheritance of color mutations can also play a significant factor
when breeding for size.

Because many autosomal recessive mutations initially appear on the
small side, these color varieties are often in need of hybrid vigor from
larger, more robust birds. However, many sex-linked recessive and
autosomal dominant mutations, bred from linebred stock where size is
set as a dominant trait, can aid in bringing recessives mutations and
even Normal Greys up in size. However, the practice of linebreeding
by utilizing proven bloodlines from aviaries that have these valuable
traits set within their lines is pivotal to such endeavors.

Although linebreeding is not the focus of this article, some brief
commentary may be helpful. Linebreeding is the systematic breeding
back of distantly related birds. Some examples of linebreeding include
grandparent to grand-offspring, aunt to nephew, great-uncle to grand-
nephew, cousin to cousin, etc.

Linebreeding is useful for establishing and setting any desirable trait
in a line, as well as breeding out undesirable, visible or hidden faults.
In the overall picture, the first step to setting a desirable trait is as
simple as selecting pairs that display the chosen quality to be passed
on to their young. Because physical traits must be visible in order to
be dominant and therefore “set” within the future line, only select birds
that visibly display the qualities you seek. Desirable traits such as
size, crest, good proportions, head qualities, and so forth must be
physically evident, or dominant, in order to be inherited by a
preponderance of future offspring.

It is difficult to know at this time whether we are truly losing a rare gift,
that is, the original Normal Grey cockatiel that is pure in its color form
without carrying any other color mutations in its genotype. History may
demonstrate our regret. Yet, because selective breeding for improved
traits has more to do with genetics and linebreeding techniques,
perhaps we are in no danger other than breeding for standards that
might lose the original characteristics of the bird we first loved in the
wild.

Because the Normal Grey cockatiel is a co-dominant, there will be
some Normal Grey offspring produced. Yet, even in the best of
situations, test breeding will be necessary in order to learn which
Normal Greys are pure homozygous, or which may be heterozygous
and therefore carry other colors in split form. At present, only Normal
Greys that are split to autosomal recessive Pied may carry tick
markings about the head and body indicating their heterozygous state.

In earlier decades, the Normal Grey cockatiel was the first choice to
add size and strength to new mutations. However, today, we have
other choices and colors to turn to, providing these exceptional traits
are set into their lines. As long as we continue to produce both Normal
Greys along with healthy color mutations that excel in traits such as
size, vigor, fertility, and exceptional parenting skills, we are continuing
to breed responsibly.

Nevertheless, the question must be asked, will the original Normal
Grey that is found only in the wild flocks in the Australian Outback still
grace our aviaries in years to come? I still remember the impressive
flocks I saw of sizeable Normal Greys feeding in the fields and flying
overhead in the wilds of St. George in the Australian Outback. For the
aviculturist who maintains one of the few breeding studs of
homozygous Normal Greys, it could possibly prove to be that
proverbial pot of gold at the end of the rainbow.

Brief Article Legend:

Chromosome: A set of threadlike structures composed of DNA and a
protein that form in the nucleus of a cell when it begins to divide.
Chromosomes travel in pairs and carry a bird’s genes that determine
its hereditary characteristics.

Dominant: A hereditary trait that is visual or expressed over a
recessive trait. The Normal Grey found in its wild form is dominant. At
the time of this writing, the Dominant Silver is the only dominant
mutation in cockatiels.

Gene: The basic physical unit of heredity that controls all traits (visual
or hidden) in a bird. Genes are inherited from both parents and are
passed on to offspring.

Heterozygous: In brief: unidentical genes reside on chromosomes for
a given hereditary characteristic. For example, “Np” is heterozygous
for Normal split to Pied. The term “split” is used in aviculture to mean
heterozygous.

Homozygous: In brief: identical genes reside on chromosomes for a
given hereditary characteristic. For example, “pp” is homozygous
(visible) for the Pied mutation.

Genotype: The full genetic makeup of an individual organism.
Mutation: Any change in the genetic information of a hereditary
characteristic. In color breeding, any variety other than Normal Grey.

Autosomal Recessive: In color breeding, these mutations are carried
on the autosomes (i.e., any chromosome that is not sex-linked).
Examples of autosomal recessive mutations include: Pied, Silver,
Fallow, Whiteface, Pastelface (Pastel), Suffused Yellow, and
Goldcheek.

Sex-linked Recessive: In color breeding, these are the genes located
on the pair of sex chromosomes and are therefore linked to the parent’
s gender. Some examples of sex-linked color mutations include:
Lutino, Cinnamon, Pearl, and Yellowcheek.

Split: An avicultural term that means the same as heterozygous, where
a cockatiel has dissimilar gene pairs for a hereditary characteristic. A
cockatiel that is split only carries the genes for that mutation but does
not visibly show it. For example, a Normal Grey split to Lutino appears
as a Normal Grey but carries the mutation for Lutino that will be
inherited by some of its offspring.

c.2007 Nancy J. Mello
Click on image to enlarge