Term | Definition |
Sex Chromosome | One of the pair of chromosomes that determine the sex of an individual. |
Autosome | Any chromosome that is not a sex chromosome. |
Sex-Linked Trait | A trait that is determined by a gene found on one of the sex chromosomes, such as the X chromosome or the Y chromosome in humans. |
Linked Gene | Pairs of genes that tend to be inherited together. |
Chromosome Map | A diagram of gene positions on a chromosome. |
Map Unit | A frequency of crossing-over of 1 percent. |
Germ-Cell Mutation | Occur in an organism's gametes, do not affect the organism itself, but can be passed to offspring. |
Somatic-Cell Mutation | Take place in an organism's body cells, do affect the organism. Cannot be inherited. |
Lethal Mutation | A gene or chromosomal mutation that influences the development of an organism in such a way that the organism cannot survive. |
Deletion | The loss of a part of DNA from a chromosome. |
Inversion | A reversal in the order of the genes, or of a chromosome segment, within a chromosome. |
Translocation | The movement of a segment of DNA from one chromosome to another, which results in a change in the position of the segment; also the movement of soluble nutrients from one part of a plant to another. |
Nondisjunction | The failure of homologous chromosomes to separate during meiosis I or the failure of sister chromatids to separate during mitosis or meiosis II. |
Point Mutation | A mutation in which only one nucleotide or nitrogenous base in a gene is changed. |
Substitution | A mutation in which a nucleotide or a codon in DNA is replaced with a different nucleotide. |
Frameshift Mutation | A mutation, such as the insertion or deletion of nucleotide in a coding sequence, that results in the misreading of the code during translation because of a change in the reading frame. |
Insertion Mutation | One or more nucleotides are added to a gene, which can also result in a frameshift mutation. |
Pedigree | A diagram that shows the occurrence of a genetic trait in several generations of a family. |
Carrier | An individual who has one copy of a recessive autosomal allele that causes disease in the homozygous condition. |
Genetic Disorder | An inherited disease or disorder that is caused by a mutation in a gene or by a chromosomal defect. |
Polygenic | Characters that are influenced by several genes. |
Complex Character | Characters that are influenced strongly both by the environment and by genes. |
Multiple Allele | More than two alleles (versions of the gene) for a genetic trait. |
Codominance | A condition in which both alleles for a gene are fully expressed. |
Incomplete Dominance | A condition in which a trait in an individual is intermediate between the phenotype of the individual's two parents because the dominant allele is unable to express itself fully. |
Sex-Influenced Trait | An autosomal trait that is influenced by the presence of male or female sex hormones. |
Huntington's disease | A rare hereditary disease of the brain characterized by involuntary movements of the limbs or face, decreasing mental abilities, and eventual death. |
Amniocentesis | A procedure used in fetal diagnosis in which amniotic fluid is removed from the uterus of the pregnant woman. |
Chorionic Villi Sampling | A procedure in which the chorionic villi to are analyzed to diagnose fetal genotypes. |
Genetic Counseling | The process of testing and informing potential parents about their genetic makeup and the likelihood that they will have offspring with genetic defects or hereditary diseases. |
Gene Therapy | A technique that places a gene into a cell to correct a hereditary disease or to improve the genome. |