A polled animal is one that was born without horns. The polled trait is determined by a genetic variation on cattle chromosome 1.
Virtually all polled Dexters in the United States descend from a bull named Saltaire Platinum, whose semen was imported from England by Fred Chesterley. The bull's granddam is believed to represent a fresh mutation. A fresh mutation is a term used to describe an animal who carries a genetic variation not found in it's parents. Platinum's grandmother had two horned parents, but had no horns. This is impossible except in the instance of a fresh mutation in the animal's DNA.
Buyers looking for polled cattle must be careful. Since polledness is a dominant trait, there are no "hidden" recessive polled genes lurking in horned animals. A horned animal out of one or even two polled parents does not carry the polled gene. Breeders who are not aware of this fact will market horned animals as carriers of the polled trait.
This is not to say that horned animals from the Platinum line are not desirable. The Platinum line has more to offer than just the lack of horns. As well as a nice stocky build, the line also has nice udder characteristics.
The following represents the inheritance of polledness in cattle and the ratios of horned and polled animals you would get with various breedings. Letters are used in clinical genetics to represent alleles or different forms of a particular gene. This is a single gene trait, so each animal has two alleles - one from each parent. Since polled is dominant is gets the big P and since horns is recessive, it gets the little p. (See the page on genetics terms for more clarification.)
pp: This animal has horns. An animal must have two genes for horns to have horns.
Pp: This animal would be polled, and carry a recessive gene for horns.
PP: This animal is polled, and does not carry the gene for horns.
Horned(pp) X Horned(pp) =
All horned(pp) offspring.
Polled(Pp) X Horned(pp) =
1/2 polled(Pp), 1/2 horned(pp) offspring.
Polled(Pp) X Polled(Pp) =
1/4 polled(PP), 1/2 polled(Pp), 1/4 horned(pp) offspring You will not be able to tell the PP and Pp animals apart, as they are both polled.
Homozygous polled(PP) X Horned(pp) =
All polled(Pp) offspring.
Homozygous polled(PP) X Homozygous Polled(PP) =
All homozygous polled(PP) offspring.
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GENETIC TERMS
Allele: Genes come in pairs (one from the father, one from the mother). An allele is either of the two paired genes affecting an inherited trait
Carrier: An animal having a recessive gene in its genetic make-up. A black animal that has a hidden recessive Dun gene, could be termed a carrier of dun. Sometimes the term carrier is used in co-dominant traits.
Chromosomes: The cell material which acts as the means for transporting genes during cell division.
Codominant: an allele that causes the heterozygous form to appear like an intermediate between the homozygous recessive and the homozygous dominant form. (All three look different from each other.) Example: Short-legged, (heterozygous form) is the intermediate between the Long-legged (homozygous recessive), and Bulldog (homozygous dominant). It may be important to note that recessive, dominant, and co-dominant are clinical terms, i.e. they are based on the outward appearance of the animal.
Dominant: an allele that causes the homozygous dominant form and the heterozygous form to look the same as each other. Example: You cannot tell a homozygous polled or a heterozygous polled animal apart. They are both polled.
Gametes: Sperm and eggs.
Genes: The units or factors of heredity that are responsible for the expression of any characteristic. Genes are tiny segments of protein contained in all cells. They normally occur in pairs and form the bridge of inheritance from one generation to the next.
Genotype: The genetic make-up of an animal. Compare to Phenotype.
Recessive: an allele that affects an animal's appearance only if it's present in the homozygous state. Example: A black animal that is heterozygous for red is still black. The animal has to have two red alleles to appear red. Black is dominant, red is recessive.
Heterozygous: having two different alleles for a genetic trait.
Inbreeding: Practice of mating animals more closely related than the average of the population. Examples: full brother to sister, sire to daughter, or son to dam.
Homozygous: having identical alleles for a genetic trait.
Lethal Gene: A gene which causes the death of the calf, usually before or at birth. Most gene pairs causing inherited lethals must be in the homozygous (pure) condition to be fatal to the calf. By this definition the gene that causes the short-legged Dexter is a lethal gene, but in it’s heterozygous form – therefore not in it’s fatal form.
Mutation: A rare change in the DNA.
Phenotype: The way the animal appears. Example: An animal that is phenotypically Red may have a genotype that includes hidden Dun genes.
Probability: The likelihood, chance or odds of the occurrence of any particular event. The odds of getting a heifer are 50:50 or 1:1.
*THE ABOVE ARTICLES WERE REPRINTED WITH THE PERMISSION OF GARBRIELLA NANCI, dexters4u.com
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SALTAIRE PLATINUM
DEXTER CATTLE HAIL FROM IRELAND
(REPRINTED FROM THE RECORD STOCKMAN 12/14/2007)
One tall tale says that Kerry cattle grazing the seaweed coast of South Western Ireland mated with sea lions and produced the first Dexters. While the early history of the breed is a potpourri of fact and folklore, we do know Dexter cattle originated from that emerald land of Leprechauns. Dexters most likely evolved from the Celtic cattle that populated Ireland and date back to the Stone Age. Like Dexters, most of the Celtic cattle were predominately black although a dun cow was painted in the 1830's by William Shiels to represent Irish Dexter/Kerry cattle. Professor David Low described Dexters in 1845 as being "various colors, as black and white, or black and brown". Mr Low's publication in 1845 is also sometimes the account used for crediting a Mr. Dexter, an agent for Lord Howarden of Tipperary, for the name. Mr. Dexter is said to have selected from the best of the hardy mountain cattle of the region during the 1750's in the development of the breed. The first herd book listing Dexter and Kerry cattle was issued in 1890.
While there are reports of Dexter cattle being introduced into England earlier, in 1882 Mr. Martin J. Sutton of Kidmore Grange, Oxfordshire purchased 10 Dexters from Mr. James Robertson of La Mancha, Dublin. The breed's popularity grew and ten years later a Dexter/Kerry cattle society was formed. This small hardy breed that was utilized for milk and meat as the "poor man's cow" in its native Ireland, ironically became the adoration of the gentry and thrived on English pastures.
Dexters were also in North America prior to the 1900's. Between 1850 and 1900, Dexters were among some of the breeds of cattle imported to Hawaii. Around 1905, Dexters formed the herds for prominent individuals such as James J. Hill, Howard Gould, and August A. Busch. A herd book published in 1921 by the American Kerry and Dexter Club listed 63 registered Dexter bulls and 260 Dexter cows.
The claim that Dexters traveled on sailing ships to provide a source of milk and fresh meat seems believable given their docile temperament and broad distribution. The Irish Dexter has become the International Dexter with a growing worldwide interest. Pushed aside by larger more specialized breeds of cattle, Dexter cattle are listed as rare by the American Livestock Breeds Conservancy. In recent years their numbers have been rising as this naturally small breed has found favor among small landowners in North America, Britain, Australia, New Zealand, South Africa, Germany, and Holland. Whether it is a frozen tundra or tropical heat this ancient breed has probably been there. Today, this smallest of the European cattle breeds continues to sail into the hearts of everyone and continues to be hardy enough to establish itself everywhere.
all polled Dexters in the United States descend from a bull named Saltaire Platinum, whose semen was imported from England by Fred Chesterley. The bull's granddam is believed to represent a fresh mutation. A fresh mutation is a term used to describe an animal who carries a genetic variation not found in it's parents. Platinum's grandmother had two horned parents, but had no horns. This is impossible except in the instance of a fresh mutation in the animal's DNA.
