Human genetic disorder is caused by nondisjunction which is the failure of chromosomes to replicate during the Anaphase II. Genes lacking chromosomes are not able to produce an embryo which is viable. Nondisjunction is most often linked with 21st chromosome giving rise to Down syndrome which increases chances of developing Alzheimer's disease. Human genetic disorder is caused by abnormal genes groups which are passed down from one generation to another. Spontaneous mutation of genes is caused by error in the replication of DNA resulting in substitution base or insertion or deletion of one or two pair base from the DNA. Other disorder like somatic genetic disease is caused by sudden appearance of abnormal type of gene in one part of the body like cancer. Others like chromosomal abnormality are caused by abnormalities in the structure of chromosomes causing Down syndrome (Green and Waterston, 1968).