Genetic counselling

Genetic counselling, or "counseling", is how clients are advised about genetic disorders. Genetic disorders, by definition, can be passed on in heredity. Example: many descendents of Queen Victoria carried one or both alleles for haemophilia. It was a hereditary disease in European royal families.
Clients with a disorder may be interested in the probability of transmitting a genetic disorder to their children. They may ask what the options are to prevent, avoid or improve it.
Genetic counsellors.
Facilities and rules vary in different countries. In the United States the National Society of Genetic Counselors defines genetic counselling as: 
A genetic counsellor is an expert with a Master of Science degree in genetic counseling. In the United States they are certified by the American Board of Genetic Counseling. Most enter the field from biology, genetics, nursing, psychology, public health and social work. Genetic counsellors need to be expert educators, skilled in translating ideas into terms that are easy to understand.
Reasons and results.
Families may choose to attend counselling or undergo prenatal testing for a number of reasons.
Training.
Training of genetic counselling is not done in all countries, and the service of genetic counselling is not available in all countries.
The basis.
The cost of complete genome analysis has come down so far that individual people can have their own genome analysed. 
The problem is interpret what the analysis shows. At present there are many genes whose functions are not yet known, and many alleles whose effect is not known.
Practical consequences.
Already it is possible to identify the sex of a foetus in the womb, and to identify some of the most common disorders. This may, depending on legal and religious constraints, influence abortion of the foetus in some cases. In some cases, the effects of a defect can be anticipated and prevented or cured. These issues do not affect most people today, but as genomic analysis advances, genetic counselling will become of much greater significance.
Root causes.
A number of themes occur. Almost universal is: groups which marry a restricted set of partners tend to have more genetic defects. The two most obvious cases are:
In the case of royal families there were a number of marriages of cousins and other close relationships. They suffered a disproportionate number of haemophiliacs, 
and some distorted features such as the Habsburg jaw (prognathism). It has been suggested that the Ancient Egyptian pharaohs suffered short lives because of their frequent incestuous marriages. In this connection it is interesting that Tutankhamun's mother was the full sister of his father. However, the immediate cause of his death seems to be malaria.
Ashkenazi jewery has a very sophisticated understanding of the genetic problems they face, and maintain an excellent advice service. 
In both cases the key causal element is the restricted set of permissible partners available for marriage.