Lab 11 Animal Embryology

What is embryogenesis?

The process of formation and development of an embryo

What is morphogenesis?

the biological process by which embryo cells, tissues, and organs acquire their shape and structure during development.

What is the first stage of embryogenesis?

Fertilization

What is fertilization?

The fusion of male and female gametes, resulting in a zygote.

Does sperm enter the egg at the same stage of egg maturation for all animals?

No, it is different for many animals

What stage of egg maturation does sperm enter the egg for dogs?

Prophase I

What stage of egg maturation does sperm enter the egg for starfish?

Metaphase I

What stage of egg maturation does sperm enter the egg for amphibians and most mammals?

Metaphase II

What stage of egg maturation does sperm enter the egg for sea urchins?

Ovum (end of meiosis)

What is cleavage in embryogenesis?

Rapid, multiple rounds of cell division that will form the blastula.

Why are early cleavages typically fast?

The zygote has a large volume of cytoplasm which allows the lengthy growth phase of interphase to be omitted from the mitosis process in early cleavage.

What is the cleavage pattern in protostomes such as mollusks?

spiral

What is the cleavage pattern in deuterostomes such as echinoderms (marine invertebrates) and vertebrates?

radial

The 16-23 cell stage is a solid ball of cells called what?

Morula

The morula later rearranges to form what?

Blastula

What is a Blastula?

An early stage of embryonic development, consisting of a hollow sphere of cells surrounding a fluid-filled cavity called the blastocoel.

What are the cells that surround the blastocoel called?

Blastomeres

What is Gastrulation?

A process in which the blastula folds over itself to form the three germ layers

What are the three germ layers formed during gastrulation?

Ectoderm

Endoderm

Mesoderm

What is the internal germ layer?

Endoderm

What is the middle germ layer?

Mesoderm

What is the external germ layer?

Ectoderm

What does the endoderm give rise to?

The interior linings of the digestive system and respiratory system.

What does the mesoderm give rise to?

Muscle tissue, connective tissues, and others

What does the ectoderm give rise to?

Skin and nervous system

Starfish spawn gametes into what?

seawater

Is starfish fertilization internal or external?

Mostly external

Starfish eggs are what?

isolecithal

What does isolecithal mean?

eggs have a small amount of yolk that distributes evenly in the cytoplasm

Approximately after 1 hour after fertilization the starfish zygote will go through what?

Holoblastic cleavage (divide entire zygote to produce 2 cells)

Blastomeres (in starfish embryos) will develop cilia for what purpose?

Allow the blastula to rotate and move after hatching from the surrounding membrane.

How is movement of blastula important to a developing starfish?

Movement allows the embryo to remove metabolic waste and gain oxygen (and other nutrients) by increasing surface contact with water.

Does the embryo grow during cleavage?

No, the cells multiply but the overall size of the embryo stays roughy the same.

What type of symmetry does a starfish larva have?

Bilateral symmetry

What does the process of gastrulation start with?

Invagination (the biological process where a surface or epithelial sheet folds inward to form a cavity, pouch, or tube, analogous to pushing a finger into a soft ball) of blastomeres at one pole of the embryo into the blastocoel, forming the archenteron (primitive gut).

During gatrulation the outer layer of the embryo becomes what?

The ectoderm

During gastrulation the archenteron (primitive gut) becomes what?

The endoderm

The opening of the archenteron is called what?

Blastopore

What does the blastopore mark the position of?

The anus

How is the mesoderm formed during gastrulation?

Cells disassociate from the tip of the archenteron and enter the blastopore, where they proliferate (divide) and form the mesoderm

What forms as the archenteron extends and fuses with the cell wall?

A mouth forms

Is frog egg fertilization internal or external?

External

Are frog eggs telolecithal or isolecithal?

Telolecithal

Describe a telolecithal eggs.

Eggs that have a large amount of yolk, and the distribution of the yolk is polarized (one pole of the egg has more yolk than the other)

What pole of a frog egg is lighter in color and has more yolk?

The vegetal pole

What poke of a frog egg is pigmented and has less yolk?

The animal pole

What pole does the sperm enter a frog egg?

The animal pole

Frog embryos go through first cleavage approximately how long after fertilization?

3 hours

The cleavage is what?

Holoblastic but uneven (animal pole leaves faster than vegetal pole)

Because vegetal cells are laden with yolk, gastrulation in frog eggs are carried out by what process?

Involution

During involution the animal pole in a frog egg moves what way?

Down over the vegetal cells and turns inward at the blastopore

During gastrulation the vegetal cells of a frog egg are eventually enclosed, what is left protruding from the blastopore?

Yolk plug

The mesoderm is formed from what during gastrulation of a frog embryo?

Cells at the dorsal lip of the blastopore

Chickens lay what type of eggs?

Amniotic eggs

The shell of a chicken egg is made of what?

Calcium carbonate

Describe the shell membrane of a chicken egg.

Two layers, partly made of keratin to protect from bacterial invasion

What is the chalazae of a chicken egg?

Opaque spiral ropes of egg white that hold the yolk in place

Describe the albumin of a chicken egg.

Egg whites that contain water and around 40 different types of proteins. The outer albumen is a narrow fluid layer, the thick inner albumen contains a large amount of riboflavin

What is the vitelline membrane of a chicken egg?

A clear casing that enclosed the yolk

What is the germinal disk of a chicken egg?

A 2-3 mm white spot on the surface of the yolk, it contains the nucleus of the egg cell

Is fertilization of a chicken egg internal or external?

Internal

Where does sperm enter the chicken egg?

The germinal disk

What kind of cleavage does a chicken egg undergo?

Meroblastic cleavage

Confines cell division to the germinal disk, forming a blastodisk on top of the yolk.

The blastodisk of a chicken embryo give rise to what?

Epiblast and hypoblast with a blastocoel in between

Gastrulation of a chicken egg begins as what occurs?

Cells of the epiblast migrate into a linear furrow.

What is the linear furrow of a chicken embryo called

Primitive steak

During gastrulation of a chicken egg, most migrating cells become what?

The mesoderm

During gastrulation of a chicken egg, cells that merge with the hypoblast become what?

The endoderm

The remaining epiblast (didn’ turn into the mesoderm or endoderm) of a chicken egg turn into what?

The ectoderm

What is the function of the yolk sac of a chicken egg?

Supplies nutrients to the embryo

What is the function of the amnion of a chicken egg?

Enclosed the embryo for protection

What is the function of the Atlantis of a chicken egg?

Obtains oxygen and minerals and removes waste

The chorion of a chicken egg does what?

Surrounds the embryo and yolk