| Johan Mendel | The father of modern genetics |
| True breading | If an organism has a certain characteristic that is always passed on to its offspring, we say that this organism bred true with respect to that characteristic. |
| Genotype | Two-letter set that represents the alleles an organism possesses for a certain trait. |
| Phenotype | The observable expression of an organism's genes |
| Homozygous Genotype | A genotype in which both alleles are identical |
| Heterozygous Genotype | A genotype with two different alleles |
| Dominant allele | An allele that will determine the phenotype if just one is present in the genotype |
| Recessive allele | The allele that will not determine the phenotype unless the genotype is homozygous in that allele |
| Mendel's First Principle of Genetics | The traits of an organism are determined by its genes. |
| Mendel's Second Principle of Genetics | Each organism has two alleles that make up the genotype for a given trait. |
| Mendel's Third Principle of Genetics | In sexual reproduction, each parent contributes only one of its alleles to its offspring. |
| Mendel's Fourth Principle of Genetics | In each genotype, there is a dominant allele. If it exists in an organism, the phenotype is determined by that allele. |
| Pedigree | A diagram that follows a particular phenotype through several generations. |
| Antigen | A protein that, when introduced in the blood, triggers the production of an antibody. |
| Autosomal inheritance | Inheritance of a genetic trait not on a sex chromosome |
| Sex-linked Inheritance | Inheritance of a genetic trait located on the sex chromosome |
| Mutation | A radical chemical change in one or more alleles |
| Change in Chromosome structure | A situation in which a chromosome loses or gains genes during meiosis. |
| Change in Chromosome number | A situation in which abnormal cellular events in meiosis lead to either none of a particular chromosome in the gamete or more than one chromosome in the gamete. |
