Asexual and Sexual Reproduction

• Reproduction is a fundamental biological process by which new individual organisms ("offspring") are produced from their "parents."
• Reproduction is essential for the continuation of species.

Modes of Reproduction

• There are two primary modes of reproduction: asexual and sexual.

Asexual Reproduction

• Involves a single parent.
• Offspring are genetically identical to the parent.

Budding

• A new organism develops from an outgrowth or bud on the parent.
• The bud detaches to form a new individual.
• Example: Hydra

Fragmentation

• The parent organism breaks into fragments.
• Each fragment develops into a new individual.
• Example: Starfish

Binary Fission

• A single cell divides into two identical cells.
• Common in bacteria and some protists such as Amoeba.

Sexual Reproduction

• Involves two parents.
• It involves the fusion of male and female gametes (sex cells).
• Offspring are genetically different from their parents and each other.
• This genetic variation is a key advantage in changing environments.

Gametes

• Gametes are specialized sex cells.
• Male gametes are called sperm.
• Female gametes are called eggs or ova.
• Gametes are haploid, containing half the number of chromosomes as somatic (body) cells.

Fertilization

• Fertilization is the fusion of a sperm and an egg.
• Restores the diploid number of chromosomes in the offspring.
• The resulting cell is called a zygote.

Development

• The zygote undergoes cell division and differentiation to develop into an embryo.
• This process is called embryonic development

Reproductive Systems

• Animals have specialized reproductive systems for sexual reproduction.
• These systems include organs that produce gametes and facilitate fertilization.

Male Reproductive System

• Key components include:
  • Testes: Produce sperm and testosterone
  • Sperm ducts: Transport sperm
  • Penis: Delivers sperm to the female reproductive tract

Female Reproductive System

• Key components include:
  • Ovaries: Produce eggs and estrogen/progesterone
  • Fallopian tubes (oviducts): Transport eggs and site of fertilization
  • Uterus: Site of embryonic development
  • Vagina: Receives sperm

Fertilization Types

• There are two main types of fertilization: external and internal.

External Fertilization

• Occurs outside the female's body.
• Common in aquatic animals like fish and amphibians.
• Requires a large number of eggs and sperm due to lower fertilization success rates.
• Timing is critical to ensure sperm and eggs meet.

Internal Fertilization

• Occurs inside the female's body.
• Common in terrestrial animals.
• Increases the chance of successful fertilization.
• Requires a method for sperm to be transferred to the female.

Development Types

• Following fertilization, animal development can be either oviparous, viviparous, or ovoviviparous.

Oviparous

• Animals lay eggs.
• The embryo develops outside the mother's body, nourished by the yolk in the egg.
• Examples: Birds, reptiles, amphibians, and fish

Viviparous

• Animals give birth to live young.
• The embryo develops inside the mother's body.
• The embryo receives nourishment directly from the mother.
• Examples: Most mammals

Ovoviviparous

• Animals retain eggs inside the female's body until they hatch.
• The developing embryo is nourished by the egg yolk, not directly by the mother.
• They then give birth to live young.
• Examples: Some sharks and snakes

Metamorphosis

• Some animals undergo metamorphosis, a dramatic transformation in body form during development.
• Common in insects and amphibians.

Amphibian Metamorphosis

• Example: A frog starts as a tadpole (aquatic larva) and transforms into an adult frog (terrestrial).
• Involves significant changes in body structure and physiology.

Insect Metamorphosis

• Incomplete Metamorphosis: The young (nymphs) resemble small adults and gradually develop through molting.
  • Example: Grasshoppers
• Complete Metamorphosis: The young (larvae) are very different from the adults and undergo a pupal stage before transforming.
  • Example: Butterflies

Hormonal Control

• Reproduction is regulated by hormones.
• In mammals, the hypothalamus and pituitary gland play key roles in controlling reproductive cycles and processes.
• Hormones regulate gamete production, ovulation, and pregnancy.