Chapter 21: Principles of Development

Vocabulary practice flashcards covering Chapter 21 (Principles of Development), including genetic equivalence, differential gene expression, stem cells, regulatory cascades, morphogens, Hox genes, and evo-devo concepts.

Developmental Biology

A biological discipline integrating genetics, biochemistry, cell biology, and evolution to investigate how a single fertilized egg (zygote) develops into an embryo and ultimately a functioning multicellular individual.

Genetic Equivalence

The principle that all differentiated somatic cells in an individual organism contain the exact same genes and complete genome as the original zygote, as demonstrated by nuclear transplantation and animal cloning.

Differential Gene Expression

The expression of different subsets of genes in different cell types, which drives cell differentiation despite all cells having identical genomes.

Meristems

Populations of specialized, undifferentiated cells in plants that retain the ability to divide and proliferate throughout the organism's entire life.

Stem Cells

Undifferentiated animal cells present in the embryo and adult that retain the potential to proliferate and produce specialized cell types.

Self-Renewal

A defining characteristic of stem cells to undergo cell divisions that produce more undifferentiated stem cells, maintaining the stem cell population over time.

Terminally Differentiated Cells

Cells that have completed the differentiation cascade, possess all their specialized structural and functional characteristics, and generally can no longer divide.

Cell-Cell Interactions

Signaling processes involving signals diffused through extracellular fluid, displayed on adjacent cell surfaces, or bound to the extracellular matrix that alter patterns of gene expression in target cells.

Cytoplasmic Determinants

Regulatory molecules unequally distributed within the cytoplasm of an egg or parent cell that are partitioned into specific daughter cells during division to specify distinct cell fates.

Induction

A mechanism of cell differentiation where an external signal produced by neighboring cells is received by one cell, directing it to specialize along a pathway different from uninduced cells.

Gastrulation

An early developmental process in animals during which cells rearrange and migrate into three distinctive types of embryonic tissue layers that give rise to adult organs.

Programmed Cell Death (Apoptosis)

A tightly regulated developmental process that eliminates specific cells at predetermined times and locations as tissues and organs take shape.

Caenorhabditis elegans (C. elegans)

A transparent nematode model organism whose adult body contains approximately 1000 cells and undergoes programmed cell death in exactly 131 specific cells during development.

Pattern Formation

The series of events and molecular signals that establish spatial organization, body axes, and structural positions within an embryo.

Morphogen

A pattern-formation substance distributed in a concentration gradient that provides embryonic cells with specific spatial information depending on the local concentration detected.

Bicoid

A maternal effect gene and morphogen in Drosophila whose protein product forms an anterior-to-posterior concentration gradient, acting as a transcription factor to promote anterior structures.

Genetic Regulatory Cascade

A linked hierarchy of regulatory genes where the activation of one set of master genes triggers the sequential expression of downstream regulatory genes, supplying progressively finer spatial details.

Maternal Effect Genes

Genes provided by the mother that encode morphogens (such as Bicoid) to establish the primary anterior-posterior axis of the early embryo.

Gap Genes

A class of segmentation genes controlled by maternal effect products that organize embryonic cells into broad regions along the anterior-posterior axis.

Pair-Rule Genes

Segmentation genes expressed in alternating bands that define and demarcate the boundaries of individual body segments.

Segment Polarity Genes

Segmentation genes expressed within portions of each segment to establish subregions and delineate boundaries within individual segments.

Homeotic Genes (Hox Genes)

A conserved family of regulatory genes that encode transcription factors specifying the identity and appropriate structural role of each body segment along the anterior-posterior axis.

Ultrabithorax (Ubx) Mutation

A homeotic mutation in Drosophila where a segment identity error leads to the development of an extra pair of wings in place of halteres.

Antennapedia Mutation

A homeotic mutation in Drosophila where leg structures develop ectopically on the head in place of antennae.

Sonic Hedgehog (SHH)

An essential signaling protein produced by limb bud cells that directs vertebrate limb patterning and outgrowth along the skeletal axes.

ZRS Enhancer

A conserved limb-specific regulatory enhancer that controls the expression of Sonic hedgehog (SHH); mutations or loss of function in this enhancer are linked to limb reduction in snakes.

Evolutionary Developmental Biology (Evo-Devo)

The study of how evolutionary modifications in developmental gene expression and ancestral regulatory mechanisms lead to morphological novelty and diverse body plans.