| A | B |
|---|
| trait | A characteristic that an organism can pass on to its offspring through its genes. |
| heredity | The passing of traits from parents to offspring. |
| genetics | The scientific study of heredity. |
| purebred | An organism that always produces offspring with the same form of a trait as the parent. |
| gene | A segment of DNA on a chromosome that codes for a specific trait. |
| alleles | The different forms of a gene. |
| dominant allele | An allele whose trait always shows up in the organism when the allele is present. |
| recessive allele | An allele that is masked when a dominant allele is present. |
| hybrid | An organism that has two different alleles for a trait; an organism that is heterozygous for a particular trait. |
| probability | The likelihood that a particular event will occur. |
| Punnett square | A chart that shows all the possible combinations of alleles that can result from a genetic cross. |
| phenotype | An organism’s physical appearance, or visible traits. |
| genotype | An organism’s genetic makeup, or allele combinations. |
| homozygous | Having two identical alleles for a trait. |
| heterozygous | Having two different alleles for a trait. |
| codominance | A condition in which neither of two alleles of a gene is dominant or recessive. |
| sperm | A male sex cell. |
| egg | A female sex cell. |
| meiosis | The process that occurs in sex cells (sperm and egg) by which the number of chromosomes is reduced by half. |
| messenger RNA | RNA that copies the coded message from DNA in the nucleus and carries the message into the cytoplasm. |
| transfer RNA | RNA in the cytoplasm that carries an amino acid to the ribosome and adds it to the growing protein chain. |
| mutation | A change in a gene or chromosome. |
