Pedigree of families of 19 years young mother (a) and 26 years young mother (b) and 33 years advanced age mother (c) with DS children. The Roman number in the left side of the figure indicates the number of generations. The Arabic number below the symbol denotes the number of individuals in that generation. The number inside the symbol of grandmother represents the age when she gave birth to the mother of DS. The number inside the symbol of father and mother in the 2nd generation indicates their age when they gave birth to DS child. The arrow directed to the shaded symbol in the 3rd generation represents the DS child. These are the representative pedigrees out of 69 DS families.