Heredity

Abstract

The totality of the hereditary factors, or genes, forms the genotype,the totality of the characters or phenes, the phenotype. There is no direct relationship between the hereditary factors and phenotypic traits. Instead, the genes represent the reaction norm which leads to the manifestation of a given phenotype only through the interplay with definite internal and external conditions. The genes are bound to structures which are handed on from cell to cell and have the ability for identical reduplication. The chromosomes of the cell nucleus play a key role among these structures. Their regular distribution in the basic processes of cellular reproduction (mitosis, karyogamy, meiosis) accounts for the inheritance of most traits. In haploid cells every gene is present only once, in diploid cells twice. Corresponding genes of homologous chromosomes are called alleles.