The title of this post is a bit of a misnomer because Scientology has absolutely nothing to do with genetics. Scientology is defined as "the study and handling of the spirit in relationship to itself, universes and other life." (Definition of Scientology)
Scientology deals with the spirit and has very little interest in bodies. It's like a car and a driver. If you wanted to know how to prevent accidents you'd study the drivers, not the cars. Sure you'd be interested in air-bags and safety belts and reinforced panels, but those are there to protect the driver. If you want fewer accidents, you would address the drivers: teach them how to drive better, teach them not to drink and drive, etc. You wouldn't get very far teaching a car how to drive better.
In Scientology we are interested in the driver, not the car. The subject of genetics studies the passing on of physical traits from one generation to the next and the way these traits vary over time. It is a purely physical study and is therefore interested in the car, not the driver – the opposite to the order of importance assigned to these things in Scientology.
This spiritual orientation gives one a slightly different view of children and family. For example, my daughter is a wonderful person and some people think she looks like my side of the family and some others think she looks like her mother's. She is not very tall, which is a trait she got from her mother but her eye color is similar to mine. These are physical traits which were passed on in the usual way. But when it comes to personality, intelligence, aptitude and interests I don't look upon her as taking after me or her mother. She is a spiritual being who makes her own decisions, has her own identity and personality and these were not passed on by heredity.
Heredity and bloodlines are of very little importance when you are interested in spirits. So if anyone tells you, or you hear somewhere that Scientologists believe someone is important for purely hereditary reasons or that something in Scientology was done in order to keep some bloodline in existence then you know that the source is misinformed or lying.