| Question | Answer |
| 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 (homozygous) |
| 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; masks the recessive allele |
| 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 for a trait is dominant nor recessive ; both alleles are expressed in the offspring |
| 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 |
| mutation | a change in a gene or chromosome |
| mitosis | the stage of the cell cycle during which the cell’s nucleus divides into two new nuclei and one copy of the DNA is distributed into each daughter cell |
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Ch.18 LTI-MA 509
