The Importance of Dam Lines in Breeding

Of course everyone interested breeding equines hears all about sire lines. And from a historical point of view it is very interesting. However, genetic lineage is not only traced through the female line, there are certain genetic traits, such as a large heart and intelligence that are carried on the female X chromosome.

Maternal Grandsire effect

Thoroughbred breeders have observed that some stallions do not produce great sons, but great daughters, who then create great sons. A female has two X chromosomes (XX) and a male has an X and a Y (XY). As the X chromosome from the stallion can only be given to his daughters, his sons will never inherit those traits. It is the dam that gives the X chromosome to her offspring. Since some desired traits are passed down on only the X chromosome it makes the dam line even more important.

Mitochrondrial DNA (mtDNA)

mtDNA is present in every animal cell and is only inherited from the mother. The really neat thing is that it then allows a direct lineage to be investigated through the female lines as it does not change over long periods of time (the rate of mutation suggests 10,000 years or more ). The reliability of maternal genetic inheritance in horses has been documented in previous studies of Lippizans and Arabians.

In a study sponsored by Thoroughbred Genetics, Dr. Harrison, et al. (2006) found an association between genes and performance ability. The genes that were investigated are only on the mtDNA molecule from the dam and contribute to the energy systems utilized during performance. They concluded that there is a relationship between the dam and the type of energy system (whether the horse is a better sprinter or has more endurance) she passes on to her offspring.

“We anticipate that the data will help trainers identify from day one, optimum running distances for horses, develop appropriate training regimes and target specific races which will suit the horses’ individual genetic profiles.” (Dr Harrison)

For more information on MtDNA and its importance please visit the following websites.

Genetic Markers

Genetics and Thoroughbred history

MtDNA research in horses

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