BIOL 1082 Lecture Notes - Lecture 28: Blastula, Polyspermy, Polarity In Embryogenesis
Ch. 53 LO
Animal Development 1 Textbook Reading: Sections 53.1-53.3
1. Describe the events necessary for fertilization to occur, including the effects of sperm on eggs. List the
different ways that polyspermy is blocked.
• Fertilization- fusion of gametes to produce a new organism
• Animals- sperm fusing with ovum, leads to developments of an embryo
• Internal fertilization- inside female body
• External fertilization- outside, sea urchins
• Fertilized egg cells- zygote
• Block- opening of Na+ channels in the egg plasma membrane. Na+ flows into egg cell,
depolarizing the membrane,
o This prevents additional sperm from fusing to egg membrane
• Polyspermy- multiple sperm fertilizing one egg
2. Define the terms cleavage and blastula, describing the two major patterns of cleavage and what is
responsible for each of them. Distinguish between the cleavage patterns and blastula formation in
frogs, birds, mammals, and Drosophila.
• Cleavage- cell division with no significant growth, producing a cluster of cells that is the same
size as the original zygote
• Cleavage leads to formation of blastula
• Blastula- embryo at the early stage of development when it is a hollow ball of cells
• Gastrulation- when a blastula, made up of one layer, folds inward and enlarges to create a
gastrula which is 3 layered structure containing the 3 germs layers: ectoderm, endoderm, and
mesoderm
• Holoblastic-complete cleavage—Blastodisc
• Meuroblastic-incomplete cleavage
3. Define gastrulation, describing the germ layers that are formed and the mechanisms by which cells
move during this process. Draw figures of gastrulation in sea urchins, frogs, birds, and mammals,
comparing and contrasting the formation of the three germ layers and the effect of the amount of
yolk.
• Egg cells is generally asymmetric, havig a aial pole future ectoder ad esoder
ad a vegetal pole future edoder.
• It is covered with a protective envelope with different layers
• Gastrulation- movement of cells from the surface of the blastula to the interior at a site called
blastopore
• Ectoderm-gives rise to CNS, PNS, sensory epithelia of eye, ear, glands, enamel
• Mesoderm- gives rise to CT, cartilage, bone, muscle blood and lymph vessels
• Endoderm- gives rise to GI and respiratory tract epithelia
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