Answer with Explanation:
Heredity and environment may play a role in connection to birth defects.
For example, when it comes to heredity, some genes can be transferred to children. An example of this is the "sickle cell disease." If parents transfer two of these genes to the child, then the child will most likely inherit the disease.
Another example, when it comes to environment, the exposure of a mother to certain factors like radiation, drugs (teratogens), alcohol, etc. may result to birth defects in children. When it comes to alcohol, mothers who have been drinking alcohol while pregnant will deliver a baby with "fetal alcohol syndrome." The baby with this syndrome will have problems with his learning ability, physical disproportions (esp. the face), will be hyperactive, etc.