The 'Genetic Guide' is the same as the previous games. As stated by Lyssaria in the Virtual Families forum:
According to the genetics pattern of the game, you can get any children between the parents, the parents' heads and the heads below and above the parents' heads.
This post explains where to locate the image used (substitute "Virtual Families game folder" for "Virtual Villagers: New Believers game folder" of course

) and how to determine what children the couple will produce.
Good luck!