| Question | Answer |
| Apical Meristem | Embryonic plant tissue in the tips of roots and in the buds of shoots that supplies cells for the plant to grow in length. |
| Apoptosis | The changes that occur within a cell as it undergoes programmed cell death, which is brought about by signals that trigger the activation of a cascade of suicide proteins in the cell destined to die. |
| Cell Differentiation | The structural and functional divergence of cells as they become specialized during a multicellular organism’s development; dependent on the control of gene expression. |
| Cell Lineage | The ancestry of a cell. |
| Chimera | An organism with a mixture of genetically different cells. |
| Clone | (1) A lineage of genetically identical individuals or cells. (2) In popular usage, a single individual organism that is genetically identical to another individual. (3) As a verb, to make one or more genetic replicas of an individual or cell. |
| Cloning | Using a somatic cell from a multicellular organism to make one or more genetically identical individuals. |
| Cytoplasmic Determinants | The maternal substances in the egg that influence the course of early development by regulating the expression of genes that affect the developmental fate of cells. |
| Determination | The progressive restriction of developmental potential, causing the possible fate of each cell to become more limited as the embryo develops. |
| Egg-Polarity Gene | Another name for a maternal effect gene, a gene that helps control the orientation (polarity) of the egg. |
| Embryonic Lethal | A mutation with a phenotype leading to death at the embryo or larval stage. |
| Homeobox | A 180-nucleotide sequence within homeotic genes and some other developmental genes that is widely conserved in animals. Related sequences occur in plants and prokaryotes. |
| Homeotic Gene | Any of the genes that control the overall body plan of animals and plants by controlling the developmental fate of groups of cells. |
| Induction | The ability of one group of embryonic cells to influence the development of another. |
| Maternal Effect Gene | A gene that, when mutant in the mother, results in a mutant phenotype in the offspring, regardless of the genotype. |
| Model Organism | An organism chosen to study broad biological principles. |
| Morphogen | A substance, such as Bicoid protein, that provides positional information in the form of a concentration gradient along an embryonic axis. |
| Morphogenesis | The development of body shape and organization. |
| Organ Identity Genes | Plant homeotic genes that use positional information to determine which emerging leaves develop into which types of floral organs. |
| Pattern Formation | The ordering of cells into specific three-dimensional structures, an essential part of shaping an organism and its individual parts during development. |
| Pluripotent | Describing a stem cell, from an embryo or adult organism, that can give rise to multiple but not all differentiated cell types. |
| Positional Information | Signals to which genes regulating development respond, indicating a cell’s location relative to other cells in an embryonic structure. |
| Segmentation Gene | A gene of the embryo that directs the actual formation of segments after the embryo’s axes are defined. |
| Stem Cell | Any relatively unspecialized cell that can divide during a single division into one identical daughter cell and one more specialized daughter cell, which can undergo further differentiation. |
| Totipotent | Describing a cell that can give rise to all parts of an organism. |