Chapter 47: Animal Development Flashcards
Fertilization
the formation of a diploid zygote from a haploid egg and sperm
Polyspermy
the entry of multiple sperm nuclei into the egg
If polyspermy were to occur…
the resulting abnormal number of chromosomes
would be lethal for the embryo
Acrosomal reaction - induced by what? essential role?
an exocytotic event induced by a Ca+ influx (occurs after sperm capacitation) - essential role during fertilization is making spermatozoa able of penetrating the zona and capable of fusing with the egg plasma membrane
Acrosome
a specialized vesicle at the tip of the sperm
Cortical reaction
a process initiated during fertilization that prevents polyspermy, the fusion of multiple sperm with one egg - Enzymes and other granule contents then trigger a cortical reaction, which lifts the vitelline
layer away from the egg and hardens the layer into a protective fertilization envelope
What triggers egg activation?
In many animals, egg activation is triggered by fertilization, which increases intracellular calcium within the oocyte and thereby regulates molecular events of egg activation
Cleavage
a series of rapid cell divisions during early development; addresses the need to restore a balance between the cell’s size and its DNA content
Blastula
an animal embryo at the early stage of development when it is a hollow ball of cells
Blastomere
a cell formed by cleavage of a fertilized ovum
Blastocoel
the fluid-filled cavity of a blastula
Cortical rotation
the outer layer of the cell (the cortex) rotates relative to the inner cytoplasm (If cortical rotation is disrupted, then this organizer is never formed and the embryo becomes a mass of ventral tissue (belly piece)
Yolk
stored nutrients in the egg
Vegetal pole
yolk is concentrated toward here
Animal pole
yolk is concentrated away from here
Gastrulation
a set of cells at or near the surface of the blastula moves to an interior location, cell layers are established, and a primitive digestive tube is formed
Organogenesis
formation of organs
Morphogenesis
a biological process that causes a tissue or organ to develop its shape by controlling the spatial distribution of cells during embryonic development
Germ layers
cell layers produced during gastrulation
Ectoderm
epidermis of skin + nervous system + pituitary gland
Endoderm
lining of digestive tract
Mesoderm
third layer between endo and ectoderm - muscle, skeleton, reproductive and excretory systems
Blastocyst
the embryo has more than 100 cells arranged around a central cavity and has reached the uterus (mammalian version of blastula)
Inner cell mass
Clustered at one end of the blastocyst cavity is a group of cells which develop into embryo (source of embryonic stem cell lines)
Trophoblast
the outer epithelium of the blastocyst; implantation is initiated by this
Extraembryonic membranes (also, how many?)
arise from the embryo, but enclose specialized structures located outside the embryo; 4
Amniote
an animal whose embryo develops in an amnion (a membrane forming a fluid-filled cavity)
Neurulation
a process in which the neural plate bends up and later fuses to form the hollow tube that will eventually differentiate into the brain and the spinal cord
Notochord
a rod that extends along the dorsal side of
the chordate embryo
Induction + example
a process in which a group of cells or tissues influences the development of another group through close-range interactions
Example: formation of the neural plate
Neural tube
forms the early brain and spine
Neural crest
a set of cells that develops along the borders where the neural tube pinches off from the ectoderm (become peripheral nerves, teeth, skull bones)
Somites (and what do they form?)
blocks of mesoderm that are located on either side of the neural tube in the developing vertebrate embryo - formation of vertebrae, ribs, and associated muscles (segmentation)
Convergent extension + example
a rearrangement that causes a sheet of cells to become narrower (converge) while it becomes longer (extends)
example: gastrulation
Apoptosis
programmed cell death
Determination
the process by which a cell or group of cells becomes
committed to a particular fate
Differentiation
specialization in structure and function
Fate maps
diagrams showing the structures arising from each region of an embryo
Totipotent
can develop into all the different cell types of that species
Pattern formation
the process governing the arrangement of organs and tissues in their characteristic places in three-dimensional space
Positional information
tell a cell where it is with respect to the animal’s body axes and help to determine how the cell and its descendants will respond to molecular signaling during embryonic development (the molecular cues that control pattern formation)
apical ectodermal ridge (AER)
a thickened area of ectoderm at the tip of the bud and acts as a major signaling center to ensure proper development of a limb
zone of polarizing activity (ZPA)
a specialized block of mesodermal tissue which instructs the developing limb bud to form along the anterior/posterior axis
fertilization process - 3 steps
- sperm dissolve or penetrate any protective layer surrounding the egg to reach the plasma membrane
- molecules on the sperm surface bind to receptors on the egg surface, helping ensure that fertilization involves a sperm and egg of the same species
- changes at the surface of the egg prevent polyspermy
fast block to polyspermy
short-lasting depolarization of the egg that prevents other sperm from fusing with the eggs membrane - depolarization caused by sodium ions (No fast block to polyspermy is known in mammals)
Formation of the fertilization envelope requires…
a high concentration of calcium ions in the egg
What marks the end of fertilization?
First cell division
initial embryonic development is carried out by
mRNA and proteins
What restores balance between between the cell’s size and its DNA content?
Cleavage
Amphibians and mammals undergo what type of cleavage?
Holoblastic (little yolk)
Meroblastic cleavage
only the region of the egg lacking yolk undergoes cleavage (lots of yolk)
archenteron
embryonic alimentary cavity that develops into the digestive tract
Embryonic development begins where?
While egg is completing journey down oviduct to uterus
the human embryo develops almost
entirely from
epiblast cells
placenta
mediates the exchange of nutrients, gases, and
nitrogenous wastes between the developing embryo
and the mother
What happens when someone’s water breaks?
Amniotic fluid is released
spina bifida
occurs when a portion of the neural tube fails to develop or close properly
Cytoskeleton
Responsible for cell shape and cell migration
