It is stated that parents and grandparents usually represent the most dominant genes in the pedigree but it is not necessarily the case. You need to know the phenotype and genotype for the first six dogs: the dam, the sire, and all four grandparents. It is very helpful if you have a knowledgeable and also objective mentor who is very familiar with the breed. Hopefully the mentor has actually seen these six dogs herself and maybe even some of the siblings. If a dog shows up more than once on a pedigree, pay particular attention and research that specific dog. Thoughtful line-breeding on a particular dog within the third or fourth generation on the pedigree can have impact on the first or second generation because his genes are more concentrated and should therefore be more powerful. A dominant, line-bred great-grandsire repeated on the pedigree can contribute as much as one of the first six dogs. (The same applies to a mediocre dog who was repeated in the pedigree. He can be bad news.). Even if a male and a female are outstanding representatives of their breed it does not matter at all, unless they are genetically compatible. It means that neither the male nor the female share the same faults either visibly (dominantly) or in their genes (recessively).So take your time and thoroughly analyze everything you know about every dog on the pedigree. It needs time and patience. It needs effort. You must be free from bias and accept deviations in your own dog as well as critically look at all of the dogs that you consider for breeding. Err on the side of caution.
Inspired by the AKC Gazette, June 2008 and Show Sight Magazine 2012