Early Development in Animals Chicken or Human??. The Process of Early Development 1. Fertilization...
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Transcript of Early Development in Animals Chicken or Human??. The Process of Early Development 1. Fertilization...
Early Development in Animals
Chicken or Human??
The Process of Early Development
• 1. Fertilization• 2. Cleavage• 3. Morula• 4. Blastula • 5. Gastrulation• 6. Neurulation
• “First call mom before going nuts”
1. Fertilization
• Sperm & egg: each have haploid genomes
• Fertilization restores diploid state to make zygote
• But that is not the whole story…
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
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
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.
2. Cleavage• Taking the cytoplasm of the zygote and
repackaging it into smaller cells; it’s all about the yolk.
These are my
Eggs!
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
The Chicken and The Egg
The Chicken and The Egg
Drosophila (Fruit Flies)
• Mitosis without cytokinesis
• Nuclei migrate to periphery
Mammals have Unique Cleavage
• Rotational cleavage
4. Blastula (Non-mammalian)
Characterized by central fluid-filled cavity
Blastocyst (Mammalian)
Human Embryo Implantation
5. Gastrulation
• Cells in blastula undergo major movements and cell divisions
• Begin the formation of 3 distinct embryonic layers
Endoderm
Ectoderm
Mesoderm
The 3 Embryonic Layers
• Ectoderm– Skin– Nervous system
• Mesoderm– Muscle, bone, kidneys, blood, etc.
• Endoderm– Liver, lungs, lining of the gut
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
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
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.