Prader-Willi syndrome is caused by a missing gene on chromosome 15. Normally, parents each pass down a copy of this chromosome. The defect can occur in a couple of ways: The father's genes are missing on chromosome 15; There are defects or problems with the fatherâs genes on chromosome 15
poison meaning, definition, what is poison: a substance that can make people or animals ill or kill them if they eat or drink it: . Learn more.
1. mass noun. 1  Poison is a substance that harms or kills people or animals if they swallow it or absorb it. 2  If someone poisons another person, they kill the person or make them ill by giving them poison. 3  If you are poisoned by a substance, it makes you very ill and sometimes kills you.