1. Early Development in Animals
Chicken or Human??

2. The Process of Early Development
1. Fertilization
2. Cleavage
3. Morula
4. Blastula
5. Gastrulation
6. Neurulation
“First call mom before going nuts”

3. 1. Fertilization Sperm & egg: each have haploid genomes
Fertilization restores diploid state to make zygote
But that is not the whole story…

4. Fertilization
The cytoplasm and mitochondria are contributed only by the egg.
Mitochondrial DNA testing follows the maternal pedigree
Some mammalian genes are active in development only if they come from the egg; others are only active if they come from the sperm
Concept of “genomic imprinting”
Example of human genomic imprinting

5. Deletion of Part of Chromosome 15
Angelman Syndrome
When deletion is on maternal chromosome 15
Prader Willi Syndrome
When deletion is on paternal chromosome 15

6. A Look at Fertilization
The 1st sperm to fuse with the egg membrane wins, and there is an immediate change in the egg membrane to make it impermeable to any additional sperm.

7. When that “shutdown” doesn’t work
Molar pregnancy

8. 2. Cleavage
Taking the cytoplasm of the zygote and repackaging it into smaller cells; it’s all about the yolk.
These are my
Eggs!

9. Cleavage in Frog Eggs
Is uneven because the yolk is concentrated on 1 side of the egg
All that yolk makes it harder for cleavage furrow to form
Cells in vegetal pole are larger than those in animal pole

10. The Chicken and The Egg

11. The Chicken and The Egg

12. Drosophila (Fruit Flies)
Mitosis without cytokinesis
Nuclei migrate to periphery

13. Mammals have Unique Cleavage
Rotational cleavage

14. 3. Morula
Means “mulberry”

15. 4. Blastula (Non-mammalian)
Characterized by central fluid-filled cavity

16. Blastocyst (Mammalian)

17. Human Embryo Implantation

18. 5. Gastrulation
Cells in blastula undergo major movements and cell divisions
Begin the formation of 3 distinct embryonic layers

19. Ectoderm
Mesoderm
Endoderm

20. The 3 Embryonic Layers Ectoderm Mesoderm Endoderm Skin Nervous system
Muscle, bone, kidneys, blood, etc.
Endoderm
Liver, lungs, lining of the gut

21. 6. Neurulation
Forming an internal neural tube from an external sheet of cells
Neural plate neural groove neural tube
Neural tube becomes spinal cord; Notochord becomes vertebrae

22. 4 Extraembryonic Membranes (Birds,Reptiles)
1. Yolk sac: surrounds yolk (provides nutrients)
2. Amnion: secretes the fluid the embryo is surrounded by
3. Chorion: Outmost of the protective membranes
4. Allantois: A sac that holds nitrogenous wastes made by the embryo

23. Extraembryonic Membranes in Mammals
1. Amnion: Secretes amniotic fluid; what is tested in amniocentesis; what “breaks” in labor
2. Chorion: The chorion, together with part of the uterine wall, make the placenta.
3. Yolk sac: Mammalian don’t have a yolk.
4. Allantois: Not needed as much; nitrogenous wastes go across the placenta and are excreted by mom’s kidneys.