zygote divides gradually to form millions of cells by which we are created. then what's the problem with the disabled ones who are disabled by birth. there cells also divides, then why they are not like us?
Egg and sperm cells each contain 23 chromosomes. When they join together, they form a fertilized egg with 46 chromosomes. But sometimes something goes wrong before fertilization. An egg or sperm cell may divide incorrectly, resulting in an egg or sperm cell with too many or too few chromosomes. When this cell with the wrong number of chromosomes joins with a normal egg or sperm cell, the resulting embryo has a chromosomal abnormality. Many children with a chromosomal abnormality have mental and/or physical birth defects. Some chromosomal abnormalities result in miscarriage or stillbirth.