What is a Tail Line?

The tracing of pedigree tail lines is a breeding practice first made popular amongst Thoroughbred horse breeders.  The theory maintains that the most influential parts of a pedigree are it's outside edges or its 'tails.'  Many Thoroughbred breeders felt strongly that prominent male or female tail lines are prepotent for certain traits, however our knowledge of modern genetics and the general unpredictability of heredity seems to generally negate the value of the theory as a breeding tool.  Despite this, there are still many educated breeders of both canines and equines who subscribe to this school of thought.

*Please note:  Unless a specific variety is indicated, "Manchester Terrier" encompasses both Toy and Standard varieties.  While tail lines may have begun as predominantly Toy or Standard based, today many female tail lines cross between both varieties.  More information on specific tail lines and their founders can be located here.

To understand the theory, the following definitions are useful (adapted from Reading Your Horse's Pedigree):

The Sire Line - The top part of a pedigree tracing through the sire, to his sire, to his sire and so forth is termed "the sire line" or male tail line. This ends in the foundation sire, who is the penultimate dog to whom the sire line traces. In the case of horses, these would usually be desertbred horses whose parents are not named.  There are four foundation sires in North American Manchesters, the most prominent three of whom are Barlow's Peter, Rex and Little Jimmie.

The Dam Line - The bottom line of a pedigree descending through the dam, her dam (the granddam), etc. is termed "the dam line" or female tail line.  This ends in the taproot dam, the first recorded dam to whom that line traces.  There are seven prominent female tail lines in North America.

Except in cases where a breed's development was carefully recorded, designating a taproot dam or foundation sire in old breeds like the Manchester is dependent solely on record-keeping given that the breed assuredly existed in recognizable form before 1873 (the earliest year for which pedigree information is available).  In the Manchester's case, there are 11 tail lines currently found in the North Amrican population.

Sire and Dam Tail Lines are clearly marked in the pedigree above.

The sons of a foundation sire form the branches of the sire line.  Sometimes a sire line does not survive in male descent. In this instance, it is a sire line that is said to exist "through the middle of the pedigree" as it is found only in females.  The same applies in reverse for dam lines. Of course, this means that it is extinct as a sire/dam line per se however the genetic material of those individuals is still available.  Individuals for whom this is true in Manchester Terriers include Merry Turk (TMT male), Lane's Dan (male SMT), Wootsie (female TMT) and Sally White (female TMT), Lord Bob (male TMT) and many others.

This is not to say that a pedigree traces back to only two foundation dogs.  If, for example, a dog has been identified as representing the Barlow's Peter sire line and the Adamson's Beauty dam line, genetic material from other primary ancestors (i.e., Rex, Little Jimmie, Merry Turk, etc.) may also be present as passed down through the middle of the pedigree.  In addition to our tail line founders, our breed has many other primary recorded ancestors.  The variety of genetic combinations that can arise through the breeding of those individuals, each of whom possessed 39 pairs of chromosomes to pass on, is what forms the basis of a breed's genetic diversity. The unpredictable path those genes may take through a pedigree provides one of the most compelling arguments against the use of tail lines as a breeding tool.

Only in the case of the lone and single Y chromosome, inherited consistently down the male tail line, can the direct path of any gene be tracked in a pedigree.  Though it admittedly follows the path of the sire line, the Y chromosome is reported by scientists to have limited fecundity beyond sexual determinism (Click here for more information on X vs Y chromosomes - including photos).  That said, though there is little scientific evidence to explain it at this time, it is interesting to observe that, though today's dam lines are predominantly found in both varieties, there is very little cross-over between varieties along male tail lines.  For example, there are no male Toy Manchesters among the over 1850 direct (i.e., along tail lines) male descendents of Barlow's Peter (SMT), and only three among both Little Jimmie's (TMT) 3400+ and Rex's 2866 direct male descendents (both past and present) who were titled as Standard Manchester Terriers.  While it should be remembered that these statistics account for only those male dogs who were shown, and so consequently do not include dogs placed as pets or even breeding stock that was not shown, the almost perfect division of the varieties along male tale lines does provide a compelling argument for the theory.  It should also be noted that these statistics do not account for female descendants of a specific male tail line who would have received an X from their fathers regardless of tail line.

Regardless of the merit of tail lines as a tool in modern breeding, their value from a historical perspective is unequivocal.  Following tail lines gives us a glimpse back at the individuals whose genetic make-up - whose mere existence - has profoundly affected the breed we work to mold and preserve today.

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