Genes are contained in chromosomes, which are in the cell nucleus.
A chromosome contains hundreds to thousands of genes.
Every normal human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes.
A trait is any gene-determined characteristic and is often determined by more than one gene.
Some traits are caused by mutated genes that are inherited or that are the result of a new gene mutation.
Proteins are probably the most important class of material in the body. Proteins are not just building blocks for muscles, connective tissues, skin, and other structures. They also are needed to make enzymes. Enzymes are complex proteins that control and carry out nearly all chemical processes and reactions within the body. The body produces thousands of different enzymes. Thus, the entire structure and function of the body is governed by the types and amounts of proteins the body synthesizes. Protein synthesis is controlled by genes, which are contained on chromosomes.
The genotype (or genome) is a person’s unique combination of genes or genetic makeup. Thus, the genotype is a complete set of instructions on how that person’s body synthesizes proteins and thus how that body is supposed to be built and function.
The phenotype is the actual structure and function of a person’s body. The phenotype is how the genotype manifests in a person—not all the instructions in the genotype may be carried out (or expressed). Whether and how a gene is expressed is determined not only by the genotype but also by the environment (including illnesses and diet) and other factors, some of which are unknown.
A karyotype is a picture of the full set of chromosomes in a person’s cells.
Genes
Humans have about 20,000 to 23,000 genes.
DNA
Genes consist of deoxyribonucleic acid (DNA). DNA contains the code, or blueprint, used to synthesize a protein. Genes vary in size, depending on the sizes of the proteins for which they code. Each DNA molecule is a long double helix that resembles a spiral staircase containing millions of steps. The steps of the staircase consist of pairs of four types of molecules called bases (nucleotides). In each step, the base adenine (A) is paired with the base thymine (T), or the base guanine (G) is paired with the base cytosine (C). Each extremely long DNA molecule is coiled up inside one of the chromosomes.
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