22.1 Principles of Animal Development

• Development begins when a sperm fertilizes an egg.
• The first stages of embryonic development in animals lead to the establishment of the embryonic germ layers.
• The presence of yolk affects the manner in which animal embryos go through the early developmental stages.
• In vertebrates, the nervous system develops above the notochord after formation of a neural tube.
• Cytoplasmic segregation and induction help bring out cellular differentiation and morphogenesis.
• Developmental genetics has benefited from research into the development of Caenorhabditis elegans, a roundworm, and Drosophila melanogaster, a fly.
• Homeotic genes are involved in shaping the outward appearance of animals.

1. What is the role of the acrosome during fertilization?
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2. In what way does the presence of yolk in an egg make a difference during development?
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3. Explain what is meant by "cellular differentiation" and "morphogenesis."
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4. What is the function of homeotic genes?
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Essential Study Partner
    Fertilization
    Cell Differentiation

Art Quiz
    Gastrulation – Mammal
    Embryos and Evolutionary History
    Allometric Growth

General Biology Weblinks
    Developmental Biology

Case Study
    Development

22.2 Human Embryonic and Fetal Development

• Humans, like chicks, are dependent upon extraembryonic membranes that perform various services that contribute to development.
• Human development consists of embryonic and fetal development.
• Humans are placental mammals; the placenta is a unique organ where exchange between fetal blood and mother's blood takes place.
• Birth is a multistage process that includes delivery of the child and the extraembryonic membranes.

1. In what way are extraembryonic membranes evolutionarily significant?
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2. During what stage of development are all the main organ systems present if not fully developed?
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Essential Study Partner
    Early Development
    Human Development
    Hormones and Pregnancy
    Preembryonic Development
    Embryonic & Fetal Development
    Parturition

Art Quizzes
    Placenta
    Extraembryonic Membranes – Mammalian Embryo (1)
    Extraembryonic Membranes – Mammalian Embryo (2)

Labeling Exercises
Human Extraembryonic Membranes (38.0K)
Anatomy of the Breast (36.0K)

Case Studies
    Embryonic Stem Cells: The Future of Organ Transplants
    The Case of the Embryos Without Parents
    Frozen Embryos

22.3 Human Development after Birth

• Investigation into aging shows hope of identifying underlying causes of degeneration and prolonging the health span of individuals.

1. What habits can be adopted to ensure that an individual ages healthfully?
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Essential Study Partner
    Postnatal Period
    Aging - Skin

Case Study
    Treatment of Critically Ill Newborns