Development AxolotlChicken. Gametogenesis The formation of gametes occurs within the gonads (ovaries and testes.) Spermatogonia and oogonia undergo mitosis.

Development

Axolotl Chicken

GametogenesisThe formation of gametes occurs within the gonads (ovaries and testes.)

Spermatogonia and oogonia undergo mitosis to produce primary spermatocytes and oocytes.

Primary gametocytes undergo meiosis twice to produce four spermatozoa or a single ovum.

Fertilization

The haploid egg and haploid sperm unite resulting in a diploid zygote.

Cell Cleavage Rapid divisions increase

cell numbers with no increase in size

1st Cleavage = 2 cells 2nd Cleavage = 4 cells 3rd Cleavage = 8 cells 4th Cleavage = 16 cells 5th Cleavage = 32 cells

(morula) Hollow ball of cells

(blastula) forms with a fluid filled cavity in the center (blastocoel)

Gastrulation

Invagination (denting inward) and involution (rolling inward) of cells producing blastopore.

The 3 primary germ layers are established: EctodermMesodermEndoderm

Gastrulation in Aquatic Vertebrates

Ectoderm formed as cells from the animal pole surround larger yolk cells which form the endoderm.

Mesoderm formed at an involuting dorsal lip at the blastopore (see models)

Gastrulation in reptiles, birds, and mammals

The cells of the blastodisc which are adjacent to the yolk become endoderm.

Mesoderm is formed at the involuting primitive streak (an elongated blastopore) on the dorsal surface of the blastodisc.

Germ Layer Development

EctodermNervous system, cornea and lens of eye, epidermis of

skin, epithelial lining of mouth and rectum

MesodermCirculatory system, segmented muscles, skeleton,

kidney, gonads, outer covering of internal organs, lining of thoracic and abdominal cavities

EndodermPharynx, liver, pancreas, lining of digestive tract,

lining of respiratory tract

Cleavage (2 cells) Cleavage (4 cells) Blastula Early Gastrula

Late Gastrula Early Neurula Early Tail Bud Late Tail Bud

Axolotl Development

Chick Embryo Development

4 day embryo removed from the egg:

http://www.youtube.com/watch?v=Bzvpa1SaGgY

9 day embryo inside egg:http://www.youtube.com/watch?

v=Tjeq58oLdVk

Fertilized egg to a baby chickhttp://www.youtube.com/watch?v=kwGkkOeoLTg&feature=related

Candling: Interpreting what you see…

Freshly laid egg (air pocket and yolk are visible): if it is over a week

old it is not fertile

Fertile egg at approximately 5 days old. Notice the faint blood vessels.

Opaque egg: the chick has developed to the point that you

can’t see through the egg at all.

This egg is opaque, but it has a large, off-center air pocket. It could contain a dead-in-shell chick, or it

could be an old rotten egg.

Chicken Egg Candling

• Unfertilized Chicken Egg • Fertilized Chicken Egg

Today’s Tasks• Station 1: Model amphibian development

– Sketch 1 stage & label layers & other identifiable structures• Station 2: Preserved and live frog embryos

– 1 sketch any stage• Label developmental stage and identifiable structures

– Discuss questions in your discussion• Station 3-4: Live axolotl, frog & killifish embryos

– 2 sketches of axolotls at different developmental stages– 2 sketches of killifish at different developmental stages

• Label developmental stages, and any of the following you can find: yolk, head, tail, dorsal/ ventral sides, eyes, blood vessels, heart

– Discuss questions in your discussion• Station 5: Chick Embryos

– 2 sketches at different developmental stages• Refer to description card to label all identifiable parts

– Discuss questions in your discussion