1. Gamete Production:
- Male animals produce sperm cells (gametes) in their testes.
- Female animals produce egg cells (gametes) in their ovaries.
2. Mating and Fertilization:
- Internal fertilization: In most animals, the sperm fertilizes the egg inside the female's body. This usually involves a process called copulation, where the male deposits sperm into the female's reproductive tract.
- External fertilization: In some animals, like fish and amphibians, fertilization occurs outside the female's body. The female releases eggs into the water, and the male releases sperm that fertilizes them.
3. Development:
- Once the egg is fertilized, it becomes a zygote.
- The zygote undergoes cleavage, a series of cell divisions that results in a ball of cells called a blastula.
- The blastula undergoes gastrulation, forming the three primary germ layers (ectoderm, mesoderm, and endoderm).
- These germ layers develop into the various tissues and organs of the developing embryo.
4. Gestation/Incubation:
- Gestation (in mammals) refers to the period of time during which the embryo develops inside the mother's body.
- Incubation (in birds, reptiles, and some fish) refers to the period of time during which the eggs are kept warm, allowing the embryo to develop inside the egg.
5. Birth/Hatching:
- Birth occurs when the fully developed offspring is expelled from the mother's body.
- Hatching occurs when the offspring breaks out of the egg.
Variations:
- Animals reproduce in a variety of ways, with some variations depending on species and environment.
- Some animals are viviparous, giving birth to live young.
- Others are oviparous, laying eggs that hatch outside the mother's body.
- A few species are ovoviviparous, where eggs develop inside the mother's body but hatch outside.
Key Points:
- Sexual reproduction involves the combination of genetic material from two parents.
- This process leads to genetic diversity in offspring, which can increase the chances of survival in changing environments.
- Reproduction is a vital process for the continuation of species.