فحص الإخصاب الداخلي في الوراثة

Internal Fertilization in Genetics

Overview

• Concept: Internal fertilization refers to the process by which sperm fertilizes an egg inside the female's body.
  • Three types: oviparity, ovoviparity, and viviparity.
  • Occurs most commonly in land-based animals, but also used by some aquatic animals.
• Advantages: Protects fertilized eggs from environmental hazards, reduces predation on offspring, enhances specificity of male selection.
• Disadvantages: Lower production rate compared to external fertilization, requires specialized delivery mechanisms, environments need to be controlled.

Types of Internal Fertilization

Oviparity

• Eggs are laid outside the female's body and receive nourishment from the yolk.
• Common in bony fish, many reptiles, most amphibians, two mammals, and all birds.
• Shell type varies between soft and hard, depending on the species.
• Found in chickens, turtles, and some snakes.

Ovoviparity

• Eggs remain within the female until they are ready to hatch.
• Embryo obtains nourishment from the yolk.
• Occurs in some bony fish, sharks, lizards, snakes, and invertebrates.
• Examples include guppies, some sharks, and the Madagascar hissing cockroach.

Viviparity

• Young develop within the female and are born alive.
• Nourished by maternal blood via a placenta.
• Characteristic of mammals, some cartilaginous fish, and a few reptiles.
• Higher survival rate due to protection from external hazards.

Comparison with External Fertilization

Advantages of Internal Fertilization

• Protection against dehydration on land.
• Reduced risk of predation on offspring.
• Enhanced fertilization specificity.

Disadvantages of Internal Fertilization

• Lower overall reproductive output.
• Requires specialized delivery mechanisms.
• Environmental conditions must be carefully managed.

Evolution of Reproduction

• Multicellular organisms developed specialized cells, tissues, and organs.
• Early evolution saw the emergence of internal fertilization strategies.
• Currently prevalent in various groups across the tree of life.