| 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).
|
 |
|
|
| amino acids | The chief components of proteins. Each "word" in the genetic code stands for a specific amino acid.
|
|
|
|
| chromosomes | Strands of DNA in the nucleus of a cell.
|
|
|
|
| codominant | When both alleles of a pair are expressed in the phenotype.
|
|
|
|
| codon | The three-base sequence that codes for a specific amino acid. Technically, the sequence on the mRNA.
|
|
|
|
| crossing over | When sections of chromosomes switch between chromosome pairs during meiosis. See also recombination.
|
|
|
|
| deoxyribonucleic acid (DNA) | The molecule that carries the genetic code.
|
|
|
|
| dominant | In a heterozygous pair of alleles, the one that is expressed in the phenotype. Compare with recessive.
|
|
|
|
| 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.
|
|
|
|
| enzymes | Proteins that control chemical processes.
|
|
|
|
| gametes | The cells of sexual reproduction, commonly sperm and egg, which contain only half the chromosomes of a normal cell.
|
|
|
|
| genes | Those portions of the DNA molecule that code for specific proteins.
|
|
|
|
| genome | The total genetic endowment of an organism.
|
|
|
|
| genotypes | The alleles possessed by an organism. See also phenotypes.
|
|
|
|
| heterozygous | Having two different alleles in a gene pair. Compare with homozygous.
|
|
|
|
| homozygous | Having two of the same allele in a gene pair. Compare with heterozygous.
|
|
|
|
| independent assortment | When genes on different chromosomes segregate to gametes independently of one another.
|
|
|
|
| linkage | When genes occur on the same chromosome and are inherited together.
|
|
|
|
| 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. See also mitosis.
|
|
|
|
| Mendelian genetics | The basic laws of inheritance, discovered by Gregor Mendel in the nineteenth century.
|
|
|
|
| messenger ribonucleic acid (mRNA) | The molecule that carries the genetic code out of the nucleus for translation into proteins. See also transfer RNA.
|
|
|
|
| mitosis | The process of cell division that results in two exact copies of the original cell. See also meiosis.
|
|
|
|
| monogenic | A trait coded for by a single gene. The ABO blood group system is a monogenic trait. Compare with polygenic.
|
|
|
|
| mutation | Any mistake in an organism's genetic code.
|
|
|
|
| nucleotide | The basic building block of DNA and RNA, made up of a sugar, a phosphate, and one of four bases.
|
|
|
|
| particulate | The idea that biological traits are controlled by individual factors rather than by a single all-encompassing hereditary agent.
|
|
|
|
| phenotype | The chemical or physical results of the genetic code. See also genotypes.
|
|
|
|
| polygenic | A trait coded for by more than one gene. Skin color is a polygenic trait. Compare with monogenic.
|
|
|
|
| proteins | Molecules that make cells and carry out cellular functions. Proteins are made of amino acids.
|
|
|
|
| protein synthesis | The process by which the genetic code puts together proteins in the cell.
|
|
|
|
| recessive | The allele of a heterozygous pair that is not expressed. For a recessive allele to be expressed it must be homozygous. Compare with dominant.
|
|
|
|
| recombination | The exchange of genetic material between pairs of chromosomes during meiosis. An important source of genetic variation. See also crossing over.
|
|
|
|
| replication | The copying of the genetic code during cell division.
|
|
|
|
| segregation | In genetics, the breaking up of allele pairs in the production of gametes.
|
|
|
|
| transfer ribonucleic acid (tRNA) | RNA that lines up amino acids along mRNA to make proteins. See also messenger RNA.
|
|
|
|
| zygote | The fertilized egg before cell division begins.
|
2002 McGraw-Hill Higher Education