PUNNETT SQUARE THE PRESERVATION BREEDERS CAN UTILIZE POPULATION GENETICS
W hat are some of the craziest things you have ever heard someone say about the heritability of traits where it con- cerns breeding dogs? Are there still some “old tales” you hear from time to time? Some recent ones that I have heard include “crossing colors dilutes the richness of black” and “you’ll never be able to breed away from the reproductive problems—they’re just part of the breed.” In spite of what people may think, believe, or feel, we are at a remarkable crossroads in time, where scientific theories of the 19th Century have paved the way for revolutionary 21st Century technology. What our predecessors, 40-60 years ago, were merely observing as correlations of heritability in the whelping box can now be analytically predicted with DNA obtained from blood samples and cheek swabs. Let’s take a look back at some of the history on genetics. We’ll also dis- cuss coefficients of inbreeding and some aspects of population ecology. More importantly, what does this mean for breed preservation, and why is an understanding of “population” so important? THE PRINCIPLES OF HEREDITY Gregor Mendel is recognized in the biological sciences for discovering the principles of heredity. Originally from Brno in the modern Czech Repub- lic, Mendel’s scientific work during the mid-nineteenth century focused on cross-pollination of pea plants, wherein he was able to describe the resul- tant expression of dominant and recessive traits. At the time, this work was ground-breaking and revolutionary, but it took another 35 years before it was widely acknowledged and accepted. Going hand-in-hand with Mendel’s inheritance of traits is the Punnett Square. Most of us who breed dogs are already familiar with this. A surpris- ing number of us, I have learned, have never heard of it. Named for Reginald Punnett, a British geneticist of the late nineteenth and early 20th centuries, the Punnett Square is a tool used by biologists to predict the probability of genotype outcomes. That is, what will be inherited in the offspring of two parents. For example, a color trait in dogs, like black, is dominant, the K locus, and when it is recessive, it allows for the expression of colors other than those controlled by the E locus. Where “Kb” is dominant and “ky” is reces- sive, and two parents each with a genotype of “Kbky” are bred together, then we would be interested to see a Punnett Square revealing a 25% probability of dominant black offspring, a 50% chance of black offspring carrying reces- sive black, and 25% probability of offspring that are not black. Therefore, it would also be interesting to know which other color alleles the parents are carrying in order to predict the potential genotype and phenotype of that other 25% that will not be black.
BY KEVIN E. HOLMES
Miniature Schnauzers owned by Silvia Soos-Kazel, Crown Point Miniature Schnauzers, New York, USA.
190 | SHOWSIGHT MAGAZINE, NOVEMBER 2021
Powered by FlippingBook