Diagrams are the best way of showing relationships clearly. There are several systems in common use and each is designed for a special purpose. The following diagrams show the most common methods:-
The arrows represent the genetic contribution of each parent to his or her offspring. With the first and second methods the sexes are denoted by the usual sex symbols and , or they may be obvious from the first names.
A diamond denotes that the sex of the person was unknown to the recorder of the pedigree. A number enclosed in an open symbol indicates the number of sibs of the same sex who are not listed separately. If an individual possesses the trait whose inheritance forms the subject of the pedigree, he or she is said to be 'affected' and is designated by a black symbol. A hollow circle or square signifies absence of the trait ('not affected'). In the above pedigree the marriage of II2 and II3 was childless and II5 and II6 are sibs whose parents are not included in the pedigree. The twins III4 and III5, are identical, as indicated by the short vertical line descending from the sibship line. The twins III6 and III7 are non-identical, as shown by their separate connection with the sibship line. Further examples are shown below:
Open circles and squares are sometimes used as an alternative to the symbols and to denote the sexes when unusual names are encountered (see here)
For display purposes there are four basic forms:-
The amount of information to include for each person or family is limited by the space available. Dates of birth, death or marriage should have priority. If space is limited, locations where people were born, lived, married and died may have to be restricted to early members of the family and where there was a migration to a different area or country. With occupations, only unusual professions or ranks should be included. In both cases extra information should be kept in a separate record.
If the scope of the family tree is very large, different branches of the family could be presented on separate sheets in such a way that when they are all placed together they make an expanded composite record. Where data have been collected from several researchers who have emphasised their own sides of the family, one has to be ruthless in giving priority to ones own family at the expense of more distant collaterals.
Standard formats which sometimes appear in books on genealogy as prepared charts are never very successful. The problem is that they give equal weighting to all branches of the family. On the one hand, this wastes space because some ancestors can not be traced, and on the other, families vary in size so that not enough space is given to some families and too much to others. For correct spacing each family tree should be specially planned either manually or by computer.
Shown below is how a pedigree should be presented for relationship calculations:
Most pedigree diagrams used in genealogy follow the format described here with vertical and horizontal lines linking the subjects:
Unfortunately, this type of diagram is unsuitable for determining the number and lengths of paths between related individuals. It also suffers from the disadvantage, that if there has been any inbreeding, some individuals may appear more than once in the pedigree. This is particularly true of Pedigree Certificates issued by the Kennel Club and Cattle Breed Societies, which always show 2 parents, 4 grandparents, 8 great-grandparents and so on. For example, the following pedigree for a Great Dane dog (M), showed that he was the result of a first cousin mating. It was taken from the Kennel Club diagram supplied by the breeder:
To avoid these difficulties, it is important that all pedigree diagrams are first converted to the 'path' format (shown below), checking that each individual is only included once, before starting any relationship calculations: