Early Frog Development

• Frogs


  • Carnivorous
  • Eat insects, spiders, and other small animals
  • Leave the water and live on land
  • Can jump great distances to avoid predators
• Frog life cycle


  1. Egg

  2. Cleavage

  3. Gastrulation

  4. Neurulation

  5. Organogenesis

  6. Tadpole

  7. Metamorphosis into a froglet

  8. Adult frog
• Frog egg


  • Female frogs lay their eggs in water, typically in a gelatinous mass
  • Protects against bacteria and attracts and activates sperm
  • Animal pole (darker) is more active and contains the nucleus, meiotic divisions occur
  • Vegetative pole (lighter) has less active cytoplasm and contains most of the yolk
• Cleavage


  Fertilization triggers a rapid series of cell divisions, resulting in a ball of cells called a blastula
• Gastrulation


  1. Cells produced during cleavage begin to move relative to each other, changing their local environment and encountering new cells

  2. Establishes the three primary germ layers: ectoderm, mesoderm, and endoderm
• Germ layers


  • Ectoderm (outer layer) forms skin, nervous system, and sensory organs
  • Mesoderm (middle layer) forms muscles, bones, skeleton, circulatory system, and excretory system
  • Endoderm (inner layer) forms lining of digestive tract and respiratory system
• Gastrulation process


  1. Dorsal lip of blastopore appears, cells change shape and push inward

  2. Additional cells roll inward over the dorsal lip to form endoderm and mesoderm

  3. Ectoderm cells change shape and begin spreading over the outer surface

  4. Blastopore lip grows on both sides, forming a circle that becomes smaller as ectoderm spreads downward

  5. Endoderm-lined archenteron replaces the blastocoel, three germ layers in place
• Cell movements in gastrulation

  • Involution: single layer of cells curves under itself to form two layers
  • Invagination: epithelial sheet bends inward to form an in pocketing
  • Ingression: cells leave an epithelial sheet by transforming into freely migrating mesenchyme cells
  • Intercalation, cell crawling, and cell shape changes result in a sheet of cells covering a surface
  • Convergent extension: cell intercalation and elongation to turn a short/wide tissue into a long/narrow tissue
• Neurulation


  Neural plate aligns length-wise with the mid-dorsal region, forms the central nervous system including brain & spinal cord
• Organogenesis


  Germ layers differentiate into specific tissues and organs: ectoderm forms skin, mesoderm forms muscles/bones/circulatory system, endoderm forms digestive/respiratory lining
• Tadpole


  • Streamlined body with tail for propulsion, feathery external gills for underwater respiration
  • Feeds on algae and microorganisms using a specialized feeding apparatus
• Metamorphosis


  Tadpole develops legs and lungs, tail is reabsorbed into the body, becomes a froglet
• Changes during metamorphosis


  • Hindlimbs appear as buds and grow into functional legs
  • Forelimbs develop later within the operculum and emerge
  • Tail undergoes programmed cell death and is reabsorbed
  • Gills become less prominent as lungs develop, allowing air breathing
  • Herbivorous digestive tract is modified
• Froglet


  Miniature version of an adult frog that can breathe both air and water, continues to grow and develop into an adult frog
• Adult frog


  Fully grown, capable of reproducing and continuing the cycle of life
• The life cycle of a frog begins when a female frog lays her eggs in water
• The fertilized egg undergoes mitotic divisions, cleaving into progressively smaller cells - a ball of cells called a blastula
• The blastula undergoes gastrulation, during which the embryo reorganizes and establishes the three primary germ layers
• From the ectoderm arises the neural plate, which folds inwards to form the neural tube during neurulation
• Each germ layer differentiates into specific tissues and organs during organogenesis
• The eggs hatch into tadpoles, which have gills and live in the water
• As the tadpoles grow, they undergo metamorphosis and develop legs, lungs, and other features that allow them to live on land
• The tadpoles transform into froglets, which have four legs and a tail
• The froglet's tail eventually disappears, and it becomes an adult frog that can reproduce and start the cycle anew
• During neurulation, the neural tube forms from the ectoderm layer.
• Neurulation occurs when the neural tube forms from the ectoderm layer.
• During gastrulation in frog development, the blastula reorganizes into three germ layers: ectoderm, mesoderm, and endoderm.
• The fertilized egg of a frog, known as a zygote, undergoes cleavage, forming a solid ball of cells called a morula.
• Gastrulation involves the formation of three germ layers (endoderm, mesoderm, ectoderm) from the inner cell mass.
• The gastrulation stage involves the formation of three germ layers (endoderm, mesoderm, ectoderm) from the inner cell mass.
• Frogs undergo external fertilization, where the female releases eggs and the male fertilizes them with sperm outside of the body.
• The blastula is formed by the division of cells.
• Gastrulation is the process by which cells move around during embryonic development to form different parts of the body.
• In amphibians, the CNS consists of the brain and spinal cord.
• Gastrulation is the process by which cells move around during embryonic development.
• Neurulation is important because it establishes the central nervous system (CNS) of the embryo.
• Cleavage is the process by which the zygote divides repeatedly to form smaller cells.
• In gastrulation, cells migrate to form three layers (ectoderm, mesoderm, endoderm) within the embryo.
• In amphibians like frogs, embryonic development is characterized by rapid growth and differentiation of tissues and organs.
• Cleavage is the division of a single-celled organism into multiple smaller cells.