DEVELOPMENTAL BIOLOGY

• As an embryo, One of the critical differences between you and a machine is that a machine is never required to function until after it is built. Every multicellular organism has to function even as it builds itself. Most human embryos die before being born
• Multicellular organism do not spring forth fully formed. Rather, they arise by a relatively slow process of progressive change (Development)
• Zygote


  The fertilized egg, which divides mitotically to produce all the cell of the body
• Embryology


  The branch of animal biology that studies the prenatal development of gametes, fertilization and development of embryology and fetuses
• Teratology


  The study of congenital disorders that occur before birth
• Developmental Biology


  The discipline that studied embryonic and other developmental process
• Development accomplishes 2 major objectives: (1) it generates cellular diversity and order within the individual organism; (2) it ensures the continuity of life from one generation to the next
• Differentiation


  The generation of cellular diversity from a single cell, the fertilized egg
• Morphogenesis


  The creation of ordered form, involving coordinating cell growth, cell migration, and cell death
• Growth


  The regulation of cell division to control the size of body parts
• Reproduction

  The transmission of genetic instructions from one generation to the next via specialized germ cells
• Regeneration


  The capacity of some organisms to regrow lost body parts, including the use of stem cells
• Environmental integration


  The influence of environmental cues on the development of organisms
• Evolution

  Inherited changes in development that create new body forms over generations
• Embryogenesis is the stages of development between fertilization and hatching (or birth)
• Fertilization

  1. Fusion of sperm and egg cells

  2. Formation of pronuclei

  3. Combination of parental genomes to form a zygote
• Cleavage

  1. Rapid mitotic divisions of the zygote

  2. Formation of blastomeres

  3. Formation of a blastula
• Gastrulation

  1. Extensive cell rearrangements

  2. Formation of the three germ layers: endoderm, ectoderm, and mesoderm
• Organogenesis

  1. Interaction and rearrangement of cells to form tissues and organs

  2. Cell migration to final locations
• Metamorphosis

  Dramatic transformation in form and habits of a young organism to become a sexually mature adult
• Gametogenesis

  Development of gametes (sperm and eggs) from germ cells in the gonads
• Diploblastic animals have a body made of only two germ layers: ectoderm and endoderm
• Triploblastic animals have a body that arises from three primary germ layers: ectoderm, endoderm and mesoderm
• Oviparity is animals born from eggs, viviparity is animals born by live birth, and ovoviviparity is animals producing an egg that hatches inside the body
• Holoblastic cleavage


  Complete division of the entire egg into distinct blastomeres
• Meroblastic cleavage


  Incomplete cleavage due to the presence of yolk material, only part of the egg undergoes cleavage
• William Harvey concluded in 1651 that all animals develop from eggs
• Frog metamorphosis


  • Bony skull of the young frog develops
  • Horny teeth the tadpole uses to tear up pond plants disappear
  • Mouth and jaw take a new shape
  • Fly-catching tongue muscle of the frog develops
• Frog metamorphosis


  1. Germ cells (sperm and egg) begin development

  2. Germ cells undergo meiosis to become mature

  3. Mature sperm and egg nuclei unite in fertilization

  4. Fertilization restores diploid chromosome number

  5. Fertilization initiates events that lead to development and continuation of life cycle
• Oviparity


  Animals born from eggs
• Viviparity


  Animals born by live birth
• Ovoviviparity

  Animals producing an egg that hatches inside the body
• Holoblastic cleavage


  Characterized by complete cleavage that divides the whole egg into distinct and separate blastomeres
• Meroblastic cleavage


  Characterized by incomplete cleavage as a result of the presence of an impeding mass of yolk material
• William Harvey concludes that all animals even mammals originate "ex ovo omnia" ("All from the egg")


  1651
• William Harvey was the first to see the blastoderm of the chick embryo
• William Harvey first noticed that an "island" of blood tissue forms before the heart does
• William Harvey suggested that the amniotic fluid might function as a "shock absorber" for the embryo
• Marcelo Malpighi published the first microscopic account of chick development


  1672
• Marcelo Malpighi identified the neural groove, the muscle forming somites, and the first circulation of the arteries and veins to and from the yolk