In the pedigree, symbols for each generation in the family are placed in a row and numbered with Roman numerals, starting with the older generation at the top and ending with the most recent at the bottom. Within each generation, people are numbered from left to right with Arabic numerals. Siblings are listed by age, with the oldest on the left. Thus, each member of the pedigree can be identified by 2 numbers (eg, II, 4). A spouse is also assigned an identifying number.