According to Mendelian principles, it makes no difference whether a given gene (or group of genes) for a hereditary trait—color in a flower, for example—is inherited from the male parent or from the female parent. However, scientists have discovered that certain genes, depending on whether they are inherited from the male or female parent, may be inactive. The process that causes the genes to be inactive is called genomic imprinting. Scientists believe the genes are inactivated either temporarily or permanently by chemical modifications that occur during the formation of gametes. These genes cause the genetic process to act unpredictably, leading, in some cases, to the conditions that cause genetic-linked diseases.