Topic 2: Development - Early Development Comparison in Model Organisms

Vocabulary flashcards covering key terms in the early development of model organisms (sea urchin, frog, chick) and humans.

Cleavage

First stage after fertilization; rapid mitotic divisions with little or no growth, producing blastomeres.

Blastomere

A cell produced by cleavage; smaller than the original zygote.

Blastula

Hollow ball of cells with a fluid-filled cavity (blastocoel); formed after several cleavage divisions.

Blastocoel

Fluid-filled cavity inside the blastula.

Animal pole

Pole where yolk is scarce; opposite the vegetal pole.

Vegetal pole

Pole where yolk is concentrated; yolk-rich region influencing cleavage.

Cleavage furrow

Indentation on the surface of a developing embryo marking a cell boundary during division.

Holoblastic cleavage

Cleavage that passes completely through the entire egg; typical in frogs, mammals, and echinoderms.

Meroblastic cleavage

Cleavage that does not pass through the yolk-rich portion; occurs in birds, fish, and reptiles.

Grey crescent

Region opposite the sperm entry that marks the future dorsal side; contains determinants for development.

Sperm entry

Trigger that sets up the body axes; orientation of the embryo often involves cortical rotation exposing the grey crescent.

Dorsal side

Back/upper side of the embryo; associated with the grey crescent and future neural axis.

Ventral side

Underside or belly of the embryo.

Equatorial cleavage

Third cleavage plane perpendicular to the previous axis; tends to produce smaller animal-pole blastomeres.

Cytoplasmic determinants

Maternal gene products localized in the egg that direct early development before zygotic transcription.

Maternal mRNA/proteins

Maternal gene products deposited in the egg that control early development prior to zygotic genome activation.

Zygotic transcription

Activation of the zygote’s own genome to begin transcription of its genes after initial maternal control.

Xenopus

Frogs (e.g., Xenopus laevis) used as a model organism to study early vertebrate development.

Archenteron

The primitive gut; formed during gastrulation as the endoderm invaginates to create the future digestive tube.

Filopodia

Thin cellular projections that help cells attach and migrate; extend to form the archenteron in sea urchins.

Mesenchyme

Totally migratory, loosely organized mesodermal cells that give rise to connective tissues and other structures.

Ectoderm

Outer germ layer; derivatives include epidermis, nervous and sensory systems, and related organs.

Mesoderm

Middle germ layer; derivatives include skeletal, muscular, circulatory, excretory, and reproductive systems.

Endoderm

Inner germ layer; derivatives include the lining of the digestive and respiratory tracts and associated organs.

Gastrulation

Process during which the blastula reorganizes into a multilayered gastrula with three germ layers.

Blastopore

Opening formed during gastrulation; becomes the mouth in protostomes and the anus in deuterostomes.

Dorsal lip

Involution site at the dorsal side of the blastopore where cells begin to move inward.

Involution

Inward movement of cells over the dorsal lip during gastrulation.

Primitive streak

Midline thickening in avian/mammalian embryos indicating a migratory path for cells to form germ layers.

Epiblast

Upper layer of the blastoderm that gives rise to the embryo and the three germ layers.

Hypoblast

Lower layer of the blastoderm contributing to extraembryonic membranes and yolk-sac formation.

Trophoblast

Outer layer of the blastocyst that implants into the uterus and forms part of the placenta.

Inner Cell Mass (ICM)

Group of cells in the blastocyst that develops into the embryo proper; differentiates into epiblast and hypoblast.

Blastocyst

Mammalian stage of the blastula with an outer trophoblast layer and an inner cell mass.

Placenta

Temporary organ that connects fetus to the uterine wall for nutrient uptake, gas exchange, waste removal, and hormone production.

Chorion

Extraembryonic membrane forming part of the placenta and contributing to nutrient/waste exchange via chorionic villi.

Amnion

Membrane that forms the amniotic sac, providing a protective cushioning environment for the embryo.

Allantois

Extraembryonic membrane involved in nutrition and waste, connected to the umbilical cord.

Yolk sac

Extraembryonic membrane involved in early circulation and formation of the primitive gut; contributes to digestive tract development.

Extraembryonic membranes

Four membranes (amniom, yolk sac, allantois, chorion) that support embryo development outside the body.