Pleiotrophy is when a single gene influences multiple phenotypic traits that seem unrelated. An example of this is an allele ML whereby if a cat is a recessive heterozygote then the cat doesn't grow a tail and is known as a manx cat. If the cat is a recessive homozygote they do not develop properly and it is lethal. Therefore there is no true-breeding line of cats with the manx phenotype. The developmental basis of pleiotrophy is unknown but the process by which pleiotrophy works is that the pleiotropic gene codes for a product that is has a function on different targets or is used by different cells. Antagonistic pleiotrophy is when the expression of a gene results in competing effects these can be detrimental or beneficial.