The trees show solid lines between married couples and their children. Unmarried couples who have children together are shown by a solid link to the child only. The portraits of children born via alien abduction[TS2] are connected to their father and the Pollination Technician, but their parents' portraits remain separate. The portraits of Deceased Sims are grayed-out.
The family trees show the current relationship between Sims. Previous marriages are not shown. If the player clicks on a parent's portrait it will usually display his/her children in birth order, from left to right.
Usually in family trees, the husband is on the left and the wife is on the right. In matrilineal families, where the husband takes the wife's last name, the wife is on the left and the husband is on the right. This may be different in some cases though, usually due to birth order. (For examples, see the Pleasant family tree or the Tricou family tree.)
In The Sims 3, premade families seem to have only 2-3 generations (with exception of the Landgraab family), while in The Sims 2 premade families nearly always have 3-5 generations.
The Sims 2Edit
In The Sims 2, players plainly see the portraits of Sims in the family tree. A Sim's name will be shown if the player hovers the mouse on a portrait, and the player can move through the tree by clicking on portraits. If there has been a divorce in the family or if the family has an unmarried couple and the child is highlighted, links from both parents will connect to the child but those links will not connect to each other. This will also happen if a widowed parent has remarried.
If there are multiple children and the parents are not together/married, or if the child has half-siblings, the child's siblings will not completely connect to the child.
For some reason, a great-grandchild and a great-grandparent (or further) will not be shown as related in the relationship panel, even though they will be connected through the family tree. This may be because there is little chance that a great-grandchild and a great-grandparent will be alive at the same time unless the older Sim has used the Elixir of Life, or the player has used cheats to extend the older Sim's life.
The Sims 2 consolesEdit
In the console game, family trees have been simplified to parents and grandparents. When the player chooses the option to randomize their Sim they will get a family tree and genetics which might include aliens.
The Sims 3Edit
In The Sims 3 the family trees are more advanced. When a Sim is highlighted it will display information concerning that particular Sim including their name, traits, partner (if any), career and anything miscellaneous. When one Sim in the family tree is selected, mousing over a relation of theirs also displays what relation they have (e.g. Aunt, Grandfather, Son, Sister-in-Law, Step-Father) to that Sim. In the Sims 3, Great-Grandparents are also recognized as relatives [to the great grandchildren] but it spans no further than the four generations. Up to 5 generations on the family tree may be viewed at the same time. Ghosts are also visible on the family trees and will all appear grey, no matter what way they died. Simbots are shown too; their mother or father is the person that invented them and they will have relations to their siblings, nieces, etc. When Simbots die, they still show up on the family tree in their alive portraits.