| particulate | The idea that biological traits are controlled by individual factors rather than by a single all-encompassing hereditary agent.
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| genes | "Those portions of the DNA molecule that code for a functional product, usually a protein."
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| proteins | Molecules that make cells and carry out cellular functions. Proteins are made of amino acids.
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| amino acids | The chief components of proteins. Each “word” in the genetic code stands for a specific amino acid.
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| enzymes | Proteins that control chemical processes.
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| chromosomes | Strands of DNA in the nucleus of a cell.
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| deoxyribonucleic acid (DNA) | The molecule that carries the genetic code.
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| nucleotide | "The basic building block of DNA and RNA, made up of a sugar, a phosphate, and one of four bases."
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| replication | The copying of the genetic code during cell division.
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| codon | "The three-base sequence that codes for a specific amino acid. Technically, the sequence on the mRNA."
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| protein synthesis | The process by which the genetic code puts together proteins in the cell.
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| messenger ribonucleic acid (mRNA) | The molecule that carries the genetic code out of the nucleus for translation into proteins. See also transfer RNA.
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| transcription | The process during which mRNA is formed from the DNA code.
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| translation | The process during which the mRNA code builds a protein using amino acids supplied by tRNA.
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| transfer ribonucleic acid (tRNA) | RNA that lines up amino acids along mRNA to make proteins. See also messenger RNA.
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| polygenic | A trait coded for by more than one gene. Skin color is a polygenic trait.
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| monogenic | A trait coded for by a single gene. The ABO blood group system is a monogenic trait.
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| genome | The total genetic endowment of an organism.
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| Mendelian genetics | The basic laws of inheritance discovered by Gregor Mendel in the nineteenth century.
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| alleles | "Variants of a gene. Most genes possess more than one possible allele, the different alleles conveying different instructions for the development of a certain phenotype (for example, different blood types)."
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| genotypes | The alleles possessed by an organism.
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| homozygous | Having two of the same allele in a gene pair.
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| heterozygous | Having two different alleles in a gene pair.
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| phenotype | The chemical or physical results of the genetic code.
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| dominant | The allele of a heterozygous pair that is expressed in the phenotype.
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| recessive | The allele of a heterozygous pair that is not expressed. For a recessive allele to be expressed it must be homozygous.
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| codominant | When both alleles of a pair are expressed in the phenotype.
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| environmental | "Any nongenetic influence on the phenotype. Also refers to the conditions under which an organism exists, such as climate, altitude, other species, food sources, and so on."
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| mutation | Any mistake in an organism’s genetic code.
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| mitosis | The process of cell division that results in two exact copies of the original cell.
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| gametes | "The cells of sexual reproduction, commonly sperm and egg, which contain only half the chromosomes of a normal cell."
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| zygote | The fertilized egg before cell division begins.
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| segregation | "In genetics, the breaking up of allele pairs in the production of gametes."
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| meiosis | "The process of cell division in which gametes are produced, each gamete having one-half the normal complement of chromosomes and, therefore, only one allele of each original pair."
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| independent assortment | When genes on different chromosomes segregate to gametes independently of one another.
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| linkage | When genes occur on the same chromosome and are inherited together.
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| crossing over | When sections of chromosomes switch between chromosome pairs during meiosis.
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| recombination | The exchange of genetic material between pairs of chromosomes during meiosis. An important source of genetic variation.
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