BIOL 1911 Chapter Notes - Chapter 47.1: Acrosome, Polyspermy, Cytokinesis
29 Apr 2018
School
Department
Course
Professor
47 – Animal Development
• Common features of early stages of embryos from different species
• Specific patterns of gene expression in an embryo direct cells to adopt distinct functions during development
• Common set of regulatory genes
• Study of development works with to the use of model organisms
o Drosophila, sea urchin, frog, chick and nematode
• Development occurs at multiple points in the life cycle
o Ex: Major developmental period in frog = metamorphosis
o Ex: stem cells in the gonads produce eggs and sperm
• Embryonic development involves common stages that occur in a set order
o Fertilization – fusion of sperm and egg
o Cleavage stage – series of cell divisions that divide, or cleave, the embryo into many cells
▪ Generates a hallow ball of cells called a blastula
o Gastrulation – blastula folds in on itself and rearranges into a multilayered embryo, the gastrula
o Organogenesis – local changes in cell shape and large -scale changes in cell location generate the rudimentary
organs from which adult structures grow
47.1 – Fertilization and cleavage initiate embryonic
development
Fertilization
• Formation of a diploid zygote from a haploid egg and sperm
• Molecules and events at the egg surface play a crucial role in each step of fertilization
o Sperm first dissolve or penetrate protective layer surrounding the egg to reach the plasma membrane
o Molecules on the sperm surface bind to receptors on the egg surface -> ensures that fertilization involves a
sperm and egg of the same species
o Changes at the surface of the egg prevent polyspermy (entry of multiple sperm nuclei into the egg, which is a
lethal condition for the embryo)
The Acrosomal Reaction
• Sea urchins release gametes into water -> jelly coat of egg exudes soluble molecules that attract the sperm, which swim
towards the egg
• Sperm egg contacts the egg surface -> molecules in the jelly coat trigger the acrosomal reaction in the sperm
o Reaction begins with a discharge of hydrolytic enzymes form the acrosome, a specialized vesicle at the tip of
the sperm
o Enzymes partially digest jelly coat, enabling a sperm structure called the acrosomal process to form, elongate,
and penetrate the coat
find more resources at oneclass.com
find more resources at oneclass.com
