| A | B |
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| True breeding | 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. |
| Allele | One of a pair of genes that occupies the same position on homologous chromosomes |
| 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 phenotype if just one is present in the genotype |
| Recessive allele | An allele that will not determine the phenotype unless the genotype is homozygous in that allele |
| Pedigree | A diagram that follows a particular phenotype through several generations |
| Monohybrid cross | A cross between two individuals, concentrating on only one definable trait |
| Dihybrid cross | A cross between two individuals, concentrating on two definable traits |
| Autosomes | Chromosomes that do not determine the sex of an individual |
| Sex chromosomes | Chromosomes that determine the sex of an individual |
| 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 |
| Genetic disease carrier | A person who is heterozygous in a recessive genetic disorder |
| Sex-linked inheritance | Inheritance of a genetic trait located on the sex chromosomes |
| 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 |
