|The study of life is
our practices on Wildwood Farm. Whether we are training our pets,
fertilizing the gardens, or breeding chickens, we recognize the
importance of incorporating sound scientific principles. That's
one of the many reasons we find learning about biology to be so
rewarding: the immediate applications of biological knowledge to our
hobbies and lifestyle. We love to share our enthusiasm for the
subject and so have offered here a summary of a few biological
concepts and how we are applying them on our farm.
You have to love
this topic with its blend of farm practicality, cellular biology,
mathematically applications and cutting edge technology. What else
you ask for?
Follow this link to some practice
problems we have set up for you. They vary in difficulty from
gentle to moderate.
There are many good sources that summarize and explain principles of
Mendelian genetics, both on the web and in textbooks, and we encourage
you to review these sources. Here are a few links but remember to
come back here when you are done for our own particular flavor of
Chicken Genetics Links
genetics for the non-professional. I experienced a few
annoying popups at this site, but the content is worth it.
of Barbu Bantams. This site has an unfortunate background
color, but again, excellent content specific to Barbus and d'Uccle
Chickens have much to
recommend them. They are easy to keep, show a huge variety in
types, have a one year generation time, and lay eggs year round. One
hen can easily produce thiry chicks in the warm season, and more if you
were willing to raise chicks indoors.
One unusual characteristic of chickens is that unlike many organisms,
their mutations are often dominant.
Comb shape is an easily observable trait, though they have rather funny
names. Let's start with the seen-one-seen-'em
all-garden-variety-so called "wild type"
comb: the single comb.
This is the type found in the domesticated chicken's ancestor the
jungel fowl. It's the type where you take a latex
glove and blow it up and pull it over your head. It' the type
seen on the cartoon character "Foghorn Leghorn" or the Kellogs
trademark rooster. In its extreme its long and floppy, and though
some of the best laying breeds have it, it can be a disadvantage in
regions with cold winters. They are susceptible to frost bite and
such injuries can at worst kill the bird and at best slow egg
production and make the poor creature miserable. Breeds that have
big single combs include leghorns, manorcas, and
andalusians. In some breeds the combs are smaller making them
more suited for Alaskan winters. One popular such breed is the
production Barred Rock.
The single comb trait is recessive.
Another common comb shape is the rose
comb. In its perfection it
is small, bumpy, lies close to the head and has a small point on the
end. It is particularly desirable in conditions where the birds
are subjected to sub freezing weather. One of my favorite breeds
that has this comb type is the Wyandotte.
Rose comb is a dominant trait.
So let's say you take a rooster that is pure Barred Rock. He
comes from a long line of barred rocks where there has been nothing
observed but single combs. We know that he got one gene from his
sire and one gene from his dam, and that both of these comb genes were
single combs. Because those genes are the same (remember, he's
"pure"), we say he is homozygous.
And because at this time we are
only concerned with his comb,as opposed to the color of his legs or the
shape of his beak, we say he is homozygous recessive for single comb
Enough about him. Let's find him a mate. Supposed you have
a Wyandotte hen. She's a pure bred hen from a reliable
breeder and for many generations back there are nothing but rose combs
in her pedigree. She is homozygous for rose comb.
So what dy'a get when you cross a rock with a wyandotte? You do
the breeding, hatch the eggs and every single one of those adorable
chicks has a rose comb. This is because the rose comb gene is
dominant to the single comb. Such a cross produces individuals
who are heterozygous, that is,
have one gene for rose comb and one gene for single comb.
Let's do another example, that happens to be a true story. A few
years ago I bought a Wyandotte rooster from a farm that had done some
cross breeding to improve their lind of birds. The rooster was
beautiful and had a perfect rose comb. I bred him to many single
combed hens and got lots of nice chicks , half of which had single
combs and half of which had rose combs. What does that tell us
about the genetics of my Wyandotte rooster? It reveals that with
respect to comb type he was not pure, but was in fact
heterozygous. A breeding where an individual showing a dominant
trait is bred to one or more individuals with a recessive trait is
called a test cross. If
I was interested in breeding chickens who were pure for rose comb, I
would know not to use that rooster, no matter how lovely he is.
Mendel and 4H Record Books
Mendel, like many gardeners and farmers of his time, liked to try
different crosses of types in his fields, but what set him apart from
the others was that he actually took the time to record his results and
apply math to them! On one hand, that may sound like a
no-brainer, but how many of us do the same? We enjoy the
game of "what do you get when you cross a ...." but then rely on our
memories rather than writing the results down. One of the ideas
we try to impress on our 4-Hers is the importance of keeping
records. For most of us this does not come natural and that's OK,
but for the serious producer and hobbiest it is a must. The IRS
uses the keeping of records as one of their criteria to differentiate a
business from a hobby.
|To cite this page:
Dent,Susan M.. D.V.M. http://www.mtaonline.net/~docdent/ Accessed
(insert date here)
|© 2006 by
Dent.Any part of this document
may be reproduced or utilized in any form or
by any means provided proper citation and credit are given for the work
and no-cost dissemination is intended. Page last updated 12/25/06