Key terms
144 terms- Fertilization§52.1
- Union of sperm and egg restoring the diploid state
- Germ line§52.1
- Cells set aside early that will produce gametes in the adult
- Acrosome§52.1
- Enzyme-filled sac in the sperm head that digests the egg coverings
- Acrosomal process§52.1
- Actin-based projection of sea urchin sperm that spans the vitelline envelope
- Vitelline envelope§52.1
- Protein coat outside the egg plasma membrane in sea urchins and frogs
- Zona pellucida§52.1
- Glycoprotein coat surrounding the mammalian egg
- Granulosa cells§52.1
- Supporting cells surrounding the mammalian oocyte
- Cortical granules§52.1
- Vesicles under the egg membrane whose release blocks extra sperm
- Hyalin§52.1
- Sugar-rich molecule that draws water in osmotically to lift the vitelline envelope
- Fertilization envelope§52.1
- Lifted and hardened vitelline envelope after the cortical reaction
- Egg activation§52.1
- Ca²⁺-triggered burst of metabolic and protein changes after sperm fusion
- Polyspermy§52.1
- Fertilization by more than one sperm; produces a lethal polyploid zygote
- Dispermy§52.1
- Fertilization by exactly two sperm
- Fast block to polyspermy§52.1
- Brief electrical change in egg membrane potential preventing more fusion
- Slow block to polyspermy§52.1
- Cortical granule release that strips sperm receptors and hardens the coat
- Pronucleus§52.1
- Haploid sperm or egg nucleus before the two combine
- Gray crescent§52.1
- Pale cytoplasm opposite the sperm entry point in frogs; marks the future dorsal side
- Polar body§52.1
- Small cell carrying discarded chromosome sets from egg meiosis
- Parthenogenesis§52.1
- Development of an embryo from an unfertilized, activated egg
- Aster§52.1
- Microtubule array, organized by the sperm centriole, that draws the two nuclei together
- Maternal mRNA§52.1
- Message stockpiled during oogenesis that powers protein synthesis after activation
- Cleavage§52.2
- Rapid division of the zygote with no increase in embryo size
- Blastomere§52.2
- One cell of the cleaving embryo
- Animal pole§52.2
- End of the egg with less yolk; generally builds external tissues
- Vegetal pole§52.2
- Yolk-rich end of the egg; generally builds internal tissues
- Tight junction§52.2
- Protein belt sealing outer blastomeres and isolating the blastula interior
- Blastocoel§52.2
- Fluid-filled cavity of the blastula, made by Na⁺ pumping and osmosis
- Blastula§52.2
- Hollow ball of cells ending cleavage
- Blastocyst§52.2
- Mammalian blastula: trophoblast layer + blastocoel + inner cell mass
- Holoblastic cleavage§52.2
- Furrow cuts the entire egg; happens with low or moderate yolk
- Meroblastic cleavage§52.2
- Furrow cannot cut the yolk, so division is confined to a disc or rim
- Isolecithal§52.2
- Sparse, evenly spread yolk
- Mesolecithal§52.2
- Moderate yolk concentrated at the vegetal pole
- Telolecithal§52.2
- Dense yolk filling most of the egg
- Centrolecithal§52.2
- Yolk concentrated in the center of the egg
- Radial cleavage§52.2
- Holoblastic pattern with cells in neat stacked rows (echinoderms)
- Spiral cleavage§52.2
- Holoblastic pattern with daughters angled over the cells below (annelids, mollusks)
- Rotational cleavage§52.2
- Holoblastic pattern of mammals and nematodes; second division differs between the two cells
- Discoidal cleavage§52.2
- Meroblastic division confined to a disc on a big yolk (fish, reptiles, birds)
- Syncytial blastoderm§52.2
- Insect stage with many nuclei sharing one undivided cytoplasm
- Cellular blastoderm§52.2
- Insect stage after membranes form around each peripheral nucleus
- Morphogen§52.2
- Diffusible signal whose concentration gradient assigns cell fates
- Blastodisc§52.2
- Small disc of yolk-free cytoplasm on a yolky egg where cleavage occurs
- Inner cell mass (ICM)§52.2
- Cluster at one pole of the blastocyst that becomes the embryo proper
- Trophoblast§52.2
- Outer blastocyst layer that implants and helps build the placenta
- Compaction§52.2
- Flattening of 8-cell blastomeres against each other, polarizing them
- Mosaic development§52.2
- Early cells committed by inherited cytoplasmic determinants
- Regulative development§52.2
- Early cells uncommitted; the embryo compensates for a lost cell (mammals)
- Gastrulation§52.3
- Cell movements that create the three germ layers and the primitive gut
- Ectoderm§52.3
- Outer germ layer: epidermis, nervous system, sense organs
- Mesoderm§52.3
- Middle germ layer: skeleton, muscle, heart, blood, vessels, gonads, kidneys, dermis
- Endoderm§52.3
- Inner germ layer: digestive and respiratory linings, liver, pancreas, thymus, thyroid
- Invagination§52.3
- A cell sheet dents inward to form a tube; low-yolk embryos
- Involution§52.3
- A cell sheet rolls inward over another sheet; high-yolk embryos
- Ingression§52.3
- Individual cells break from a sheet and migrate alone
- Delamination§52.3
- One cell sheet splits into two layers; birds and mammals
- Lamellipodia§52.3
- Broad actin-filled extensions used to crawl over neighboring cells
- Filopodia§52.3
- Thin extensions that probe a surface then retract to pull the cell forward
- Fibronectin§52.3
- Extracellular matrix protein essential to gastrulation movement
- Vegetal plate§52.3
- Flattened vegetal-pole region where sea urchin gastrulation begins
- Primary mesenchyme cells§52.3
- Sea urchin cells that ingress and become larval-skeleton mesoderm
- Archenteron§52.3
- Primitive gut cavity formed during gastrulation
- Blastopore§52.3
- Opening of the archenteron; becomes the anus in deuterostomes
- Deuterostome§52.3
- Animal whose anus forms first and mouth second
- Dorsal lip§52.3
- Edge of the frog blastopore over which cells involute; the organizer
- Yolk plug§52.3
- Yolk-rich cells bulging in the amphibian blastopore
- Blastoderm§52.3
- Cap of cells on the yolk in bird and reptile embryos after cleavage
- Primitive streak§52.3
- Midline ingression furrow of birds and mammals; an elongated blastopore
- Amniotic cavity§52.3
- Fluid space that opens between the ICM and the embryo pole
- Amnion§52.3
- Inner membrane suspending the embryo in amniotic fluid
- Chorion§52.3
- Outermost membrane; gas exchange in birds, fetal half of the placenta in mammals
- Yolk sac§52.3
- Membrane that nourishes bird and reptile embryos; present but non-nutritive in mammals
- Allantois§52.3
- Gut outpouching storing uric acid in birds; umbilical cord vessels in mammals
- Chorioallantoic membrane§52.3
- Fused allantois and chorion; the bird embryo gas-exchange surface
- Extraembryonic coelom§52.3
- Cavity separating the chorion from the other membranes in birds
- Organogenesis§52.4
- Formation of organs in correct locations from interacting germ layers
- Homeotic gene§52.4
- Gene encoding a homeodomain transcription factor that specifies structure identity
- Sex combs reduced (Scr)§52.4
- Fly homeotic gene that permits salivary gland formation in an anterior strip
- fork head (fkh)§52.4
- Scr target gene required for salivary gland secretory cells
- Decapentaplegic (Dpp)§52.4
- Dorsal fly signal that blocks salivary glands, restricting them ventrally
- tinman§52.4
- Homeobox gene required for the Drosophila dorsal vessel (heart)
- Dorsal vessel§52.4
- The Drosophila heart equivalent, derived from mesoderm
- Branching morphogenesis§52.4
- Repeated branching of epithelial tubes; builds insect tracheae and lung airways
- branchless§52.4
- Drosophila FGF-family gene needed for tracheal branching
- Notochord§52.4
- Flexible mesoderm rod along the dorsal midline of every chordate embryo
- Neurulation§52.4
- Formation of the neural tube from the neural plate
- Neural plate§52.4
- Thickened dorsal ectoderm above the notochord
- Neural groove§52.4
- Folded neural plate before the tube closes
- Neural tube§52.4
- Hollow cylinder that becomes brain and spinal cord
- Somitomere§52.4
- Rounded block of paraxial mesoderm before it segments
- Somite§52.4
- Segmented mesoderm block giving cartilage, skeletal muscle, and dermis
- Presomitic mesoderm§52.4
- Unsegmented mesoderm behind the newest somite; source of the next ones
- Segmentation clock§52.4
- Contact-mediated signaling that times somite formation (~90 min in chick)
- Neural crest§52.4
- Migratory cells pinched off the dorsal neural tube; vertebrate hallmark
- Cranial neural crest§52.4
- Anterior crest cells forming craniofacial structures and PNS neurons and glia
- Dorsal root ganglia§52.4
- Crest-derived sensory neuron clusters linking periphery to spinal cord
- Schwann cells§52.4
- Crest-derived cells insulating peripheral nerve fibers
- Adrenal medulla§52.4
- Crest-derived endocrine tissue producing epinephrine
- N-cadherin§52.4
- Adhesion molecule crest cells down-regulate in order to leave the neural tube
- Integrin§52.4
- Receptor letting migrating cells grip extracellular matrix proteins
- Chorda-mesoderm§52.4
- Mesoderm lineage that becomes the notochord
- Paraxial mesoderm§52.4
- Mesoderm lineage giving head mesoderm and somites
- Intermediate mesoderm§52.4
- Mesoderm lineage giving kidneys and gonads
- Lateral plate mesoderm§52.4
- Mesoderm lineage giving circulatory system, cavity linings, extraembryonic tissue
- Coelom§52.4
- Body cavity formed between the two split layers of lateral mesoderm
- Hox gene complexes§52.4
- Vertebrate homeotic clusters positioning organs along the anterior–posterior axis
- Spemann–Mangold organizer§52.5
- Dorsal lip tissue that induces a second body axis when transplanted
- Organizer§52.5
- Cell cluster releasing morphogens that give neighbors positional information
- Induction§52.5
- One tissue directing the developmental fate of an adjacent tissue
- Animal cap / vegetal cap§52.5
- Isolated blastula halves used to test mesoderm induction
- Nieuwkoop center§52.5
- Cells receiving relocated dorsal determinants; induces the organizer above them
- Dorsal determinant§52.5
- Maternal molecule that moves to the future dorsal side at fertilization
- Cortical rotation§52.5
- Sperm-triggered microtubule-driven rotation of the egg cortex
- Wnt§52.5
- Signaling protein family; maternal Wnt-pathway mRNAs specify the organizer
- BMP4§52.5
- Protein made by all prospective mesoderm; more binding pushes toward ventral fates
- BMP4 antagonists§52.5
- Organizer proteins (Noggin, Chordin, Dickkopf, Cerberus) that block BMP4 receptors
- Hensen's node§52.5
- Amniote structure equivalent to the amphibian organizer
- Pattern formation§52.5
- Arranging anatomical structures in correct position and 3D orientation
- AER§52.5
- Apical ectodermal ridge; secretes FGF to drive proximal–distal limb outgrowth
- Progress zone§52.5
- Mesenchyme under the AER that sets limb identity via Hox genes
- ZPA§52.5
- Zone of polarizing activity; secretes Shh to set anterior–posterior digit identity
- Sonic hedgehog (Shh)§52.5
- ZPA morphogen; high near the ZPA gives posterior digits
- Tbx5 / Tbx4§52.5
- T-box genes expressed in forelimb and hindlimb buds respectively
- AmphiTbx4/5§52.5
- Lancelet ancestor of Tbx4 and Tbx5, expressed in the heart region
- Holt–Oram syndrome§52.5
- Human Tbx5 mutation causing combined forelimb and heart defects
- Co-option§52.5
- Evolutionary reuse of an existing gene or pathway for a new job
- Primary induction§52.5
- Signaling between the three primary germ layers (e.g. neural tube formation)
- Secondary induction§52.5
- Signaling between already-committed tissues (e.g. lens formation)
- Optic cup / lens vesicle§52.5
- Retina-forming stalk derivative and the ectoderm pocket it induces to become the lens
- Trimester§52.6
- One of three roughly three-month blocks of human gestation
- Implantation§52.6
- Trophoblast digesting into and embedding in the uterine endometrium
- Placenta§52.6
- Chorion plus maternal endometrium; exchanges materials without mixing blood
- Human chorionic gonadotropin (hCG)§52.6
- Trophoblast hormone maintaining the corpus luteum; detected by pregnancy tests
- Chorionic frondosum§52.6
- Fetal component of the placenta
- Decidua basalis§52.6
- Maternal component of the placenta
- Coccyx§52.6
- Tailbone formed by fusion of the embryonic tail bones
- Prostaglandins§52.6
- Signals that start uterine contractions at the onset of labor
- Oxytocin§52.6
- Posterior pituitary hormone driving labor contractions and milk let-down
- Neonate§52.6
- Newborn baby
- Afterbirth§52.6
- Placenta and membranes expelled after the baby
- Prolactin§52.6
- Anterior pituitary hormone stimulating mammary alveoli to make milk
- Milk let-down reflex§52.6
- Suckling triggers oxytocin, which squeezes milk out of the alveolar ducts
- Colostrum§52.6
- Yellowish antibody-rich first milk; true milk begins about 3 days after birth
- Allometric growth§52.6
- Different body parts growing at different rates, changing proportions over time