Sexual Reproduction and Fertilization

Introduction

Sexual reproduction involves the combination of genetic material from two organisms.
Specialized cells known as sex cells, or gametes, carry genetic material.
Sperm cell (male gamete)
Egg cell (female gamete)

Purpose: Transfer male genetic material to the egg.
Shape: Torpedo-like for movement.
Components:
- Head: Contains genetic material (DNA) in the nucleus and the acrosome (enzyme-filled structure for fertilization).
- Middle section: Packed with mitochondria (75-100 large mitochondria) to provide energy.
- Tail: Flagellum acts as a propeller for movement.

Shape: Round and large compared to sperm.
Size: Approximately 10,000 times more massive than sperm.
Components:
- Nucleus: Contains genetic material ready for fertilization.
- Zona pellucida: Thick outer layer made of glycoproteins, protects the egg, and interacts with sperm.
- Cytoplasm: Contains a large number of mitochondria (100,000 to 200,000) and other organelles.

Sperm Binding:
- Sperm contacts the zona pellucida and binds.
Acrosome Reaction:
- Acrosomal enzymes digest the zona pellucida, allowing sperm to approach the egg's plasma membrane.
Cortical Reaction:
- Cortical granules beneath the egg's plasma membrane release enzymes that prevent other sperm from binding (block to polyspermy).
Fusion:
- Sperm and egg plasma membranes fuse, allowing sperm genetic material transfer to egg, completing fertilization.

Mitochondria contain their own DNA.
Despite potential for sperm mitochondria transfer, the zygote's mitochondria are primarily maternal due to the vast number present in the egg compared to sperm.

Sperm Cell: Designed for mobility, carrying male genetic material with components aiding propulsion and energy provision.
Egg Cell: Larger and protected, with a thick glycoprotein layer and abundant mitochondria.
Fertilization: Involves a series of reactions ensuring single sperm entry and genetic material fusion, leading to a viable zygote formation.