An Introduction to Chicken Genetics — Chicken DNA Part I
Why Poultry Played Such an Important Role in Early Genetic Discoveries
By Doug Ottinger, Minnesota
Genetics. If you are already bored by the first word of this article, don’t worry. Most likely, you are in good company. There are a lot of fellow readers out there who are afraid that this will be a scientific article, laced with a bunch of technical terms that only a nerd, who lives in a science lab, can understand.
If you are like me, you fell in love with chickens, regardless of the fact that they have 39 pairs of chromosomes, more than 16,700 genes and most of their chromosomes are micro-chromosomes. You really did not care, and furthermore, you could probably care less to this day. Take heart! I will not be talking a lot about that kind of stuff in this series. My goal is to share some educational material and make the topics interesting at the same time.
Starting around the turn of the 20th century, interest in the field of genetics and heredity began to grow in the scientific and educational communities at an almost exponential rate. Many animals and organisms were studied, but by some estimates, no organism or animal, including humans, had any more research done on them than chickens. For the next 60 years or so, vast amounts of money and time were expended by many of the leading colleges and universities, as well as federal and state governments, to gain a better understanding of poultry genetics and breeding, and ultimately improve overall production. Poultry was a component of almost every family farm during this time. Many families relied on the production and sale of eggs, as well as butchered birds, to help makes ends meet.
Because this was such a very real economic component of life, government agricultural departments, in not only the United States and Canada, but in much of the developed world, committed notable resources to this endeavor.
Prior to the concept of genetics evolving, breeders still had a good understanding of the role that heredity and lineage played in breeding improvement. German farmers in the Pennsylvania upcountry, as early as the 1700s, were aware of the deleterious effects that too much inbreeding could have on a flock. Each spring, many farmers in the individual communities held rooster swaps with one another, to bring new blood and vigor into their poultry lines.
Meet Mr. Gregor Mendel
To fully appreciate some of the early research done with fowl, one has to understand a little history of genetic research. Almost every high school student during his or her year in biology class learns about a Monk in the 1800s, named Gregor Mendel, who was fascinated by the variations of pea vines in his garden. Between 1856 and 1863, Mendel kept copious notes on the parent plants, as well as the offspring, when the next generation of pea seed was planted, dividing the results into distinct mathematical ratios. Mendel noticed that certain traits were much more prevalent than others. Because of this, he used the terms “dominant” and “recessive” (which we still use today) to describe them.
Most students are taught how to make a little square, divide it into four sections (or more), and to put the symbols for various genetic traits (or dominant and recessive genes) on the top and side of the square’s sections. They then make simple mathematical predictions about the outcome of cross-breeding plants or animals.
Many biology teachers move as rapidly as possible through the material, teaching the students that Gregor Mendel was the father of modern genetics. (Hence the term, “Mendelian Genetics.”) However, if you could go back in time and talk with Gregor Mendel and ask him about his research work in pea-vine genetics, he would probably ask you “Mendelian … What?”
For you see, the term “genetics” was not coined until some 22 years after his death. Mendel’s studies were studies in heredity, as he termed them. If you tried to draw one of those squares (known as a “Punnell Square”), and enter the symbols for dominant and recessive pea-plant genes, poor Brother Mendel would be even more perplexed. For you see, it was a man named Reginald Punnell who came up with that little divided square many years later. And Mendel was not the one who came up with the theory of genes! However, Mendel’s work was very advanced for the time, and it cannot be undervalued. His work did help later researchers confirm some of their studies, as they achieved similar results with other organisms.
A New Study: Cross-Breeding
Another researcher, William Bateson (1861-1926), was one of the first individuals to formally study the effects of cross-breeding and heredity in chickens. Bateson was intrigued by the variations and differences in the combs in individual birds. Consequently, he began thinking of ways to conduct a study that would answer some of the whys and wherefores of the seeming vast differences of comb structure in different breeds of the genus Gallus.
Starting in 1898, Bateson began cross breeding Indian Games (pea combs), Wyandottes (rose combs), Dorkings (rose comb), and Single Comb White Leghorns. He kept precise data on his findings, of both F1 and F2 crosses. There was a distinct 3:1 ratio in the F2 generation, almost identical to the findings of Gregor Mendel many years earlier. What becomes even more interesting, however, is the fact that Bateson reportedly did not even hear of Mendel or his research until two years later in 1900. One must remember that information traveled at a crawl in this era, so this is not totally surprising. Bateson studied traits in chickens as well as several other organisms. His findings of distinct ratios coincided with the findings of Gregor Mendel, giving the first proof that Mendel’s findings on heredity applied to the animal as well as plant kingdom.
In 1902, Bateson presented his findings to the Evolution Committee of the Royal Society in London. Up until this time, Mendel’s findings had been largely discredited by the leading men of science.
Between 1900 and 1910, Bateson directed a series of informal studies in heredity and genetics at Cambridge University. Most of his students (including his wife Beatrice and her sister) were women associated with Newham College. Numerous studies in both plant and animal organisms were carried out, when Mendelian theories were not recognized as a legitimate field of study. It was Bateson who reportedly coined the word “genetics” (from the Greek word Gennos, meaning “to give birth”).
He first used the word officially, at the Third International Conference of Plant Hybridization, held in London in 1906. However, it appears that another researcher, Hugo Devries, may have well been the one who came up with the actual theory of genes. Working with another researcher, Reginald Punnell, Bateson co-discovered the theory of genetic linkage. The two researchers also founded The Journal of Genetics in 1910. One very interesting twist, however, to the story about William Bateson, is the fact that he refused to believe in the theory of chromosomes, which other researchers began to accept in the first quarter of the 20th century. It is said that he only partially accepted the theory by the time he died in 1926.
Back to Poultry DNA
The 1920s were a decade when genetic studies on fowl became more prevalent in scientific circles. Poultry breeding, genetics and biological studies, almost too numerous to count, were conducted by researchers at universities, government agricultural agencies and growing agricultural industries. Poultry had such a prominent place in the basic farm and home economy that no effort was spared in conducting studies to improve the farm and home flocks across the United States and Canada.
Genetic studies were in full swing and numerous studies involving poultry were being conducted by many leading universities. There were several reasons behind this. First, as mentioned, was the economic impact that poultry had on the basic farm and home economies. Researchers wanted to find out what factors made hens lay more, and bigger, eggs. They wanted to find out genetic effects on growth and body conformation of birds for the broiler industry. They wanted to find out how heredity and nutrition worked. In fact, just about any conceivable question was put to scientific study during these years. (One of the most comprehensive books that cites thousands of these studies, throughout its bibliographic listings, is Genetics of the Fowl, by F.B. Hutt, PhD., D.Sc. It was first published by McGraw-Hill in 1949.)
One very big problem faced by farmers and poultry men was disease and deformities that often showed up in flocks. With no understanding of what was causing the problems, there was no knowledge on how to stop these disasters as they happened. Much research was conducted in these areas and notable advances were slowly made in the eradication of disease in poultry flocks.
As The Great Depression of the 1930s worsened and changed almost every aspect of life across America, government cut very little funding for research in the fields of poultry improvement. As one looks at the number of research papers written, and sees the increase in findings made, it is evident that research in poultry was alive and well during this time. Research for home flocks continued throughout the war years of the 1940s. Many of these studies are also cited by Hutt. One interesting fact is that many of these studies, from the 1920s throughout the 1940s, involved genetic issues and referenced them, even if the research itself was not directly about genetics.
One area of extensive research, much of it conducted in the 1930s, were studies done on the endocrine systems in chickens. Numerous studies and research papers, cited by Dr. Hutt, involved studies on the thyroid glands, parathyroid glands, pituitary gland, hypothalamus, adrenals and other components affecting the endocrine system. Numerous experiments were done on birds that had thyroid glands or parathyroid glands surgically removed. Surgical techniques had advanced to a point where even the extremely small glands in the fowl could be surgically excised for research.
A better understanding of organic and biochemistry was now in place, and hormones were being better understood. Effects of hormones on growth were tested. Disease resistance was studied. Even hormonal effects on blood pressure in the capillaries could be studied by measuring the changes in blood pressure in a chicken’s comb. Cornell University performed extensive studies on eradicating Lymphomatosis, as it was called, or fowl leukemia, in chickens. Not only was much of the research on disease and endocrine systems important to agriculture, but much of it was directly transferable to studies in human anatomy, health and disease control.
Genetic studies in chickens were also preferable to many researchers, as the fairly short incubation time of 21 days could get research underway rather quickly. Any studies involving embryonic development could be easily handled by opening individual eggs, instead of having to remove embryos surgically.
Now that I have painted a somewhat broad picture of the genetic research done on chickens over the first half of the 20th century, we are ready to jump into the nuts and bolts of genetic information about chickens. But that will be in the next article. I will also share some interesting and quirky things you may not know about Flossie, Henrietta and Herkemer (or whatever the names of your pet chickens are!). Until then, enjoy the time with your birds. They are truly amazing little creatures that are just as interesting on the inside as they are on the out.
Sources:
Hutt, F.B., PhD., D.Sc., Genetics of the Fowl, McGraw-Hill Book Company, 1949.
Jull, Morley a., Poultry Husbandry, McGraw-Hill Book Company, 1951.
U.S. Department of Agriculture, Yearbook of Agriculture, Animal Diseases: 1956, Washington
CHICKEN DNA, PART 1 This is the first in a three-part series on poultry genetics by Doug Ottinger. The second article Chicken DNA Part 2 will include little-known facts about the genetic makeup of the chicken and comparisons of how much our feathered friends are like us. Part 3 will look at how genetic research changed the skin and feathers in chickens.
Doug Ottinger lives in Northwest Minnesota with his wife, Connie. They raise chickens, ducks and geese on their small hobby farm. Doug’s educational background is in agriculture, with an emphasis in poultry and avian genetics.
