ZOO: DSC-353 Reproductive and Developmental Biology

Unit 5: Post Embryonic Development

1. Metamorphosis: Amphibians and Insects
2. Regeneration: Modes and Mechanisms
3. Stem Cells (ESC) and Amniocentesis
Exam Focus: Tips, FAQs, and Mnemonics

1. Metamorphosis: Amphibians and Insects

Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation.

Amphibian Metamorphosis

Classic example: The transformation of a tadpole into an adult frog.

Morphological Changes: Loss of tail, development of limbs, and shifting from gills to lungs.
Hormonal Regulation: Primarily controlled by Thyroxine (T4) and Triiodothyronine (T3) produced by the thyroid gland.

Insect Metamorphosis

Insects exhibit two main types of metamorphosis:

Hemimetabolous (Incomplete): Egg → Nymph → Adult (e.g., Grasshoppers).
Holometabolous (Complete): Egg → Larva → Pupa → Adult (e.g., Butterflies).
Hormonal Regulation: Regulated by Ecdysone (molting hormone) and Juvenile Hormone (JH).

2. Regeneration: Modes and Mechanisms

Regeneration is the process of renewal, restoration, and growth that makes genomes, cells, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage.

Modes of Regeneration

Mode	Description	Example
Epimorphosis	Involves the proliferation of new tissues from a blastema (a mass of undifferentiated cells).	Salamander limb regeneration.
Morphallaxis	Regeneration occurs through the repatterning of existing tissues with little new growth.	Hydra.
Compensatory Regeneration	Cells divide to restore the function of an organ, but do not necessarily regrow the exact original structure.	Mammalian liver.

3. Stem Cells (ESC) and Amniocentesis

Stem Cells (ESC)

Embryonic Stem Cells (ESC) are pluripotent stem cells derived from the inner cell mass of a blastocyst.

Properties: They have the ability to differentiate into all three germ layers (ectoderm, endoderm, and mesoderm).
Applications: Used in regenerative medicine, drug testing, and studying developmental biology.

Amniocentesis

Amniocentesis is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections.

Procedure: A small amount of amniotic fluid, which contains fetal tissues, is sampled from the amniotic sac surrounding a developing fetus.
Purpose: To detect genetic disorders like Down syndrome or determine fetal lung maturity.

[Image of the amniocentesis procedure]

Exam-Oriented Focus

Exam Tip: For metamorphosis, always highlight the specific hormones involved (Thyroxine for amphibians; Ecdysone/JH for insects). These are high-yield points for marks.

Frequently Asked Questions (FAQs)

Q: What is the difference between Epimorphosis and Morphallaxis?
A: Epimorphosis requires a blastema and new cell growth, whereas Morphallaxis relies on reorganizing existing cells.
Q: Why are ESCs considered pluripotent?
A: Because they can give rise to any cell type in the adult body.
Q: What is the primary hormone triggering molting in insects?
A: Ecdysone.

Common Mistake: Do not confuse Amniocentesis with Implantation. Implantation is the attachment of the embryo to the uterus; Amniocentesis is a diagnostic test performed much later during pregnancy.

Mnemonics

E-P-I: Epimorphosis = Proliferation Involved (New growth).
M-O-R: Morphallaxis = Only Reorganizing (No blastema).