Weismann has also ingeniously argued from the structure of the egg-cell and sperm-cell, and from the way in which, and the period at which, they are derived in the course of the growth of the embryo from the egg - from the fertilized egg-cell - that it is impossible (it would be better to say highly improbable) that an alteration in parental structure could produce any exactly representative change in the substance of the germ or sperm-cells.
Each egg and sperm cell contains only one copy of chromosome and, therefore, only one copy of the RB1 gene.
Occasionally, a genetic error occurs during egg or sperm cell formation.
A child conceived with such an egg or sperm cell may inherit an incorrect number of chromosomes.
Often, the genetic material is missing due to an error in replication of an egg or sperm cell.