If each version of the same section of the chromosome make contradictory ‘recommendations’, what the body does varies. Sometimes, one reading prevails the other and the other is ignored. An ignored gene is called ‘recessive’, the opposite of that is the ‘dominant’ gene. When two genes are rivals for the same slot on a chromosome, they are called ‘alleles’ of each other. (As an example, the gene for brown eyes is usually dominant to the gene for blue eyes)