A fertilized egg (also known as a zygote), contains 23 pairs of chromosomes for a total of 46 chromosomes in the zygote. These chromosomes come from the mother via the unfertilized egg, and from the father via the sperm cell. Each of these carries 23 individual chromosomes, which are matched and paired with the 23 chromosomes from the other partner.
These paired chromosomes determine what the child’s physical characteristics will be when they are born, including hair color, eye color, skin tone, facial structure, and gender. The 46 chromosomes contained in a fertilized egg form the basic genetic makeup for the growing fetus. If there are any mutations or abnormalities in any of these chromosomes, or if there are extra or missing chromosomes, this will usually result in a birth defect.