homologous chromosomes
From Genotype to Phenotype Each human body cell has a full complement of DNA stored in 23 pairs of chromosomes. Figure 28.24 shows the pairs in a systematic arrangement called a karyotype. Among these is one pair of chromosomes, called the sex chromosomes, that determines the sex of the individual XX in females, XY in males . The remaining 22 chromosome pairs are called autosomal chromosomes. Each of these chromosomes carries hundreds or even thousands of genes, each of which codes for the assembly of a particular proteinthat is, genes are expressed as proteins. An individuals complete genetic makeup is referred to as his or her genotype. The characteristics that the genes express, whether they are physical, behavioral, or biochemical, are a persons phenotype. You inherit one chromosome in each paira full complement of 23from each parent. This occurs when the sperm and oocyte combine at the moment of your conception. Homologous chromosomesthose that make up a complementary pairhave genes for the same characteristics in the same location on the chromosome. Because one copy of a gene, an allele, is inherited from each parent, the alleles in these complementary pairs may vary. Take for example an allele that encodes for dimples. A child may inherit the allele encoding for dimples on the chromosome from the father and the allele that encodes for smooth skin no dimples on the chromosome from the mother.