Developmental Bio Test 2

in zebrafish chorion, where sperm enters

• fertilization is external
• sperm enters micropylar orifice in chorion, binds to microvilli on egg surface, and fuses with egg
• cortical granules beneath egg surface exocytose and release their contents = chorion lifts off the egg surface
• then cytoplasmic streaming happens where the nonyolk cytoplasm moves to the animal pole and forms the cytoplasmic cap
• first cleavages are vertical = one layer of blastomeres that are connected to yolk mass
• then a horizontal cleavage = outer layer of blastomeres not connected to yolk cell

• secretory vesicles containing vitelline membrane components that are released from the egg at fertilization
• vitelline membrane: extracellular membrane around a zygote

extracellular layer surrounding a fish or insect egg

meroblastic

the large cells arising from the fertilized egg by cleavage divisions

• after 9 divisions
• set of coordinated changes in the late blastula including the onset of zygotic genome transcription
• cell cycle length increases
• synchrony of divisions breaks down
• cells become more motile
• the outer blastomeres that are connected to the yolk cell sink into it = multi-nuclear syncytium that is thicker around periphery
• syncytium nuclei divide rapidly 3-4 times
• rest of yolk cell is surrounded by a thin layer of cytoplasm (no nuclei)

• results when the outer blastomeres that were connected to the yolk cell sink into it
• thicker on periphery of embryo but extends under the blastoderm

• sheet of cells
• compare to blastula which is a ball of cells
• inside consists of deep cells

• external layer of epithelial cells generated by the main blastoderm
• will form the periderm (outer layer) of the larval epidermis

• brings about the 3 germ layers
• 3 processes:
• epiboly:spreading and increase in area of a cell sheet
• involution: internalization of a cell sheet, carried out by the deep cells
• convergent extension: cell sheet elongates and narrows

lower layer that is formed when the blastoderm begins to involute

involution begins and the blastoderm becomes thicker around the margin

• dorsal region of the blastoderm
• becomes thicker
• compare to dorsal lip of Xenopus
• elongates by convergent extension
• its outer layer becomes the neural plate

• dorsal ectoderm thickens to form the neural plate
• neural plate converges toward dorsal midline and then mashes up to form neural keel (rod)
• secondary cavitation creates a neural tube
• somites form next to notochord

• constructed by labeling early cells and seeing where their descendants end up later
• constructed right before gastrulation
• lots of cell mixing

• identify recessive mutations by breeding for 3 generations
• point mutations induced with ethyl nitrosourea (ENU) in spermatogonia of the males
• in F3 generation can get homozygous mutants (but they might die so have to look at them before they do)
• now better ways to view organs individually: immunostaining, in situ hybridization, GFP

• genetic test to find if 2 recessive mutants lie in the same gene by introducing one mutation on the maternal and the other on the paternal chromosome
• if they are in different genes then the wild-type alleles should complement and show no phenotype
• if they are in same gene they will fail to complement and a phenotype will result

fertilization by multiple sperm

golgi-like body in mouse spermcontains enzymes (proteases) that digest through proteins of the follicle cell layer

mid-piece in mouse sperm that is rich in mitochondria

period of time when mammal sperm stay in female reproductive tract during which they become competent to fertilize