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| allele | one of two or more variants of a gene that determines a particular trait for a characteristic |
| codominance | in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic |
| continuous variation | a variation in a characteristic in which individuals show a range of traits with small differences between them |
| dihybrid | the result of a cross between two true-breeding parents that express different traits for two characteristics |
| discontinuous variation | a variation in a characteristic in which individuals show two, or a few, traits with large differences between them |
| dominant | describes a trait that masks the expression of another trait when both versions of the gene are present in an individual |
| epistasis | an interaction between genes such that one gene masks or interferes with the expression of another |
| F1 | the first filial generation in a cross; the offspring of the parental generation |
| F2 | the second filial generation produced when F1 individuals are self-crossed or fertilized with each other |
| genotype | the underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism |
| hemizygous | the presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant |
| heterozygous | having two different alleles for a given gene on the homologous chromosomes |
| homozygous | having two identical alleles for a given gene on the homologous chromosomes |
| hybridization | the process of mating two individuals that differ, with the goal of achieving a certain characteristic in their offspring |
| incomplete dominance | in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype |
| law of dominance | in a heterozygote, one trait will conceal the presence of another trait for the same characteristic |
| law of independent assortment | genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur |
| law of segregation | paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors |
| linkage | a phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together |
| model system | a species or biological system used to study a specific biological phenomenon to gain understanding that will be applied to other species |
| monohybrid | the result of a cross between two true-breeding parents that express different traits for only one characteristic |
| P | the parental generation in a cross |
| Punnett square | a visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid |
| phenotype | the observable traits expressed by an organism |
| recessive | describes a trait whose expression is masked by another trait when the alleles for both traits are present in an individual |
| reciprocal cross | a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross |
| recombination | the process during meiosis in which homologous chromosomes exchange linear segments of genetic material, thereby dramatically increasing genetic variation in the offspring and separating linked genes |
| test cross | a cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait |
| trait | a variation in an inherited characteristic |
| wild type | the most commonly occurring genotype or phenotype for a given characteristic found in a population |
| X-linked | a gene present on the X chromosome, but not the Y chromosome |
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