We like to think that bad environments make bad heredities and the reverse. Again this is false and was the basis of many mischievous social movements that condemned people as genetically inferior because of generations of social failure. It is also true that bad environments will stifle the potentials of most children. But a three generation welfare family may reflect bad luck rather than crummy genes. In the Middle Ages even kings were illiterate.
Real heredity is a surprise to most people.
They wonder how a child who is an albino or who has cystic fibrosis can arise when neither the normal father nor the normal mother has relatives with that condition. The geneticist has fancy names for this and calls the child homozygous and the two parents each heterozygous or hybrid. Hybrids normally do not show their hidden or recessive mutations. It does take a geneticist to work out pedigrees and figure out risks and that is why we now have genetic counselors to do that job.