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Cockatiel Genetics Made Easy!
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"Well, there is help on the horizon and anyone
seriously interested in color genetics should take
a look at Linda Rubin's book: COCKATIEL
GENETICS MADE EASY! Though this book is
primarily directed to breeders of cockatiel
mutations, there is enough information in this
volume to teach anyone the secrets of dealing
with recessive, sex-linked, and dominant
mutations.
Click to read rest of review
- Dr. Rainer R. Erhart, American Cage Bird Magazine,
Volume 65, No. 12. p. 37.
Excerpt  From Chapter 10
Combining Autosomal Multi-recessive Mutations
Up until this point, we have covered numerous combinations of sex-linked mutations, their
crossover occurrences, and have even paired them with an autosomal recessive mutation.
Therefore, we are now ready to move forward and learn to pair autosomal recessive mutations to
one another. This work will then enable us to combine multiple recessive mutations, with
sex-linked mutations in future chapters. It shall, however, require learning a new graph which in
actuality, is merely a modified version of our original graph presented in earlier chapters.

Many biology texts refer readers to the traditional Punnett Square, which is simple enough to learn
whenever considering autosomal recessive mutations. However, the problem with such a model
is that we are unable to utilize it for the many autosomal recessive mutations we may work with in
a single pair of cockatiels. Therefore, a somewhat different graph must be utilized to meet our
needs.

As we work with the modified graph, you will recognize a familiarity in the pairing of genes below.
We will call our new graph,
The Recessive Graph, which is set up exactly the same as practiced in
previous chapters, but which uses the letter "
r."


             
                                                         
r        r             r        r  


Before we master riding a bicycle, we are usually supported by a pair of training wheels to help us
learn to balance and prepare us for our solo ride. In the same manner, we shall need a devise
which will act as our own set of training wheels to facilitate practicing such graphs until we are
more comfortable "soloing" on our own.

We shall identify such "training wheels" on our recessive graph with the letter "r," which shall stand
for
recessive. While some authors might be inclined to use the letter "z" (keeping with the logic of
"X" and "Y" for sex-linkage, and "z" for autosomes), I feel the use of an "r," which stands for
(autosomal) recessive will be less confusing and easier to remember. Quite simply, "r" stands for
"recessive," which is how many breeders in the fancy refer to autosomal recessive color and
pattern mutations.

You will note the familiar recessive graph, shown above, which now contains four "training" r's, two
each for the sire, and two each for the dam. Perhaps the best way to explain the modified
recessive graph it to illustrate it by returning to our shorthand.  Let's consider an example
involving a Whiteace cock X A Whiteface/Pied hen. We remember the gene letters we have always used for these mutations from previous chapters as shown below:

                                                                                                          Example:  
Whiteface cock X Whiteface/Pied hen

                                                                                                          Where:                                                              
                                                                                                          nn = Normal Grey                                                nn = Normal Grey
                                                                                                          nw = Normal Grey/Whiteface                             np = Normal Grey/Pied
                                                                                                          ww - Whiteface                                                     pp  = Pied


We will utilize our training "r"s on the recessive graph much like we use an "X" to hold a sex-linked gene. In this manner, we will be able to work with Multiple (autosomal)
recessives, as you will see in future examples. First, however, let's graph the above example of one (autosomal) recessive mutation to a different (autosomal) recessive
mutation.

If we were to assign the recessive genes using our old method, we might want to write something like this:

                                                                                                         Sire (Whiteface) = ww nn
                                                                                                         Dam (Whiteface/Pied) = ww np

which could be interpreted as: the sire is visually a Whiteface, but lacks any genes for Pied; the dam is visually a Whiteface, and carries a single quantity for pied, therefore
also making her heterozygous or split Pied. Not only would this method be long and cumbersome to figure out (especially with multiple recessive mutations), but it is
actually unnecessary.

Our aim in this Workbook is to keep our notation as simple as possible. Do we really need all those "n"s when, for example, we know that s single quantity of an assigned
recessive gene stands for a split, and a double quantity of a recessive gene stands for a visual?

Since we know that ww = Whiteface, and np = split Pied, why didn't we simple write out: ww np?  We could have, however, we would be redundant by including an "n"
when we know only one "p" (i.e., a single quantity) represents a heterozygous or
split Pied.  However, we also know that we need to diagram a  continue                     
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