00728-A: The Role of Genetics in the Widely Differing Life Spans of the Domestic Dog
Grant Status: Closed
Grant Amount: $12,960
Dr. Keith E. Murphy, PhD, Texas A&M University
April 1, 2006 - September 30, 2006
Breed(s): -All Dogs
Project Summary It is commonly accepted in the dog world that larger breeds have shorter life expectancies that smaller breeds. This phenomenon is also seen in four strains of dwarf mice that are much smaller than average mice and exhibit longer life expectancies. Our hypothesis was that the genes responsible for allowing these dwarf mice to have longer life expectancies are also responsible for allowing small dog breeds to live longer than their larger counterparts. In order to determine if these genes were involved in life span of the dog we sequenced the genes Pitl, Propl, GHR, and Ghrhr. The sequence was determined for the following gene segments: 1000 base pairs upstream and downstream, the exons, and 100 base pairs flanking each exon.
Breeds to be examined in this SNP analysis were selected from those included in a previously completed regression analysis. The breeds were classified as small, medium, and large breeds. For each breed the reported heights and weights were entered into a formula to predict life expectancy based on height and weight and the output was compared to the reported life expectancy of the breed. Utilizing this information, three breeds were chosen from each size category, one breed having a shorter than predicted life expectancy, one breed having a life expectancy similar to that predicted by the linear regression information, and one breed having a longer than predicted life expectancy. The breeds selected for SNP analysis in the small breed category are Pomeranians, Dachshunds and Miniature Schnauzers. Breeds included in this study from the medium size category are the Basset Hound, Staffordshire Bull Terrier and Standard Schnauzer. Large breeds selected for analysis are the Bloodhound, Great Pyrenees and Giant Schnauzer. These breeds in each size class exhibit shorter than expected, expected and longer that expected life spans, respectively.
A total of 53 polymorphisms were identified (Seventeen in Ghr, 26 in Ghrhr, five in Propl, and 25 in Pitl). Ofthese 53, thirteen were ancestral SNPs in which both alleles were found in every breed analyzed and were discovered in Pitl (eight) and Ghrhr (five). Thirty-one polymorphisms with allelic frequencies of at least 10% were selected for further analysis using Fisher's exact test. However, no evidence was gathered to support our hypothesis that these genes are involved in allowing smaller breeds to outlive larger ones.