Wildwood Farm

Back to School: Biology

The study of life is integral to 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 could 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 genetics.

Chicken Genetics Links
Poutlry genetics for the non-professional.  I experienced a few annoying popups at this site, but the content is worth it.

Genetics of Barbu Bantams.  This site has an unfortunate background color, but again, excellent content specific to Barbus and d'Uccle chickens

Why Chickens?  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.

Chicken Genetics
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 trait.
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.

Test Cross
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. 


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To cite this page:
Dent,Susan M.. D.V.M. http://www.mtaonline.net/~docdent/  Accessed (insert date here)

© 2006 by  Susan 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