Читать книгу Child Development From Infancy to Adolescence - Laura E. Levine - Страница 207

Chromosomes are made of chains of genes, which consist of chains of the nucleotide bases guanine, adenine, thymine, and cytosine. The order of these bases gives a cell the instructions for producing different proteins. Genes are generally paired up, with half of each pair coming from each parent. A genotype is the genes a person has for a particular characteristic and the phenotype is the characteristics that are expressed in that person. Dominant genes are expressed in the phenotype regardless of the gene they are paired with, but recessive genes are expressed only if they are paired with another recessive gene, or if they are carried on the X chromosome of a male child with no matching gene on the Y chromosome. Each trait or behavior can be produced by the interaction of many genes, a process called polygenic inheritance. In addition, any one gene may have many different influences, called pleiotropic effects.