Klinefelter syndrome is neither dominant nor recessive- it is the result of a gamete with 2 sex chromosomes being paired with a gamete with only one. To find out if someone has Klinefelter syndrome doctors will ask questions about their health, and order a genetic test called a karyotype.

http://youtu.be/c9ne4Cwy9T4

This is a wonderful video for anyone who is just learning about Klinefelter syndrome.

This picture illustrates some common symptoms of Klinefelter syndrome. 

This picture shows the chromosome responsible for Klinefelter Syndrome