Vertebrate Zoology

Development

Based on Pough et. al, 1989. Vertebrate Zoology - 3rd Ed. MacMillan

Hickman et al., 1996. Integrated Principles of Zoology - 10th Ed. William C. Brown Publishers

Development is the progressive changes in an organism from birth to death.  There are three aspects of development: growth, differentiation,  and morphogenesis.  Growth is the result of mitosis; the body becomes larger as cells are added. Differentiation is the process by which cells specialize, and morphogenesis is the process by which the differentiated cells fuse and die to form organs.

Development starts with fertilization.  The fertilized egg, now called a zygote, undergoes mitosis or cleavage.  Eventually, a hollow ball or a flat disc of cells are formed by successive cleavages.  The formation of this ball of cells is called blastulation, and the zygote becomes a blastula.  Next, a gut is formed by a movement and infolding of cells. This process is called gastrulation, and the resulting organism a gastrula.  Another important process is neurulation or the formation of the nervous system.  Other organogenesis also follows gastrulation.  Once all of the organs are formed, all that remains for the embryo to do is to grow; and again this is done via mitosis.

Development is a very visual process.  At this point, I have neither the graphics nor the expertise to present a good discussion.  The outline below will help you check your notes against the material I present in class, and, of course, the textbook presents the material in a more coherent fashion.  You might also want to check out this on-line tutorial.

1. Fertilization
   1. chemotaxis may guide sperm to egg
   2. proteins allow for species-specific recognition
   3. acrosome releases enzymes
   4. egg changes polarity
   5. cortical granules fuse with membrane, form fertilization membrane
   6. egg and sperm nuclei fuse
   7. formation of zygote

1. Cleavage
   1. zygote becomes embryo
   2. does not increase in size
   3. individual cells called blastomeres
   4. patterns
      1. affected by amount of yolk
         1. isolecithal
            1. little yolk, evenly divided
            2. inverts, mammals
            3. holoblastic cleavage
            4. indirect development in invertebrates allows larval stage to feed, grow
            5. nourishment provided in mammalian uterus provides nutrition (direct development)
         2. mesolecithal
            1. moderate amount of yolk
            2. vegetal pole - mostly yolk
            3. animal pole - mostly cytoplasm
            4. holoblastic cleavage
               1. slower in vegetal pole
         3. teleolecithal
            1. much yolk
            2. most concentrated at one end
            3. meroblastic cleavage - partial
      2. Types of cleavage:
         1. radial cleavage
            1. produces layers of cells
            2. also known as regulative
               1. if cells separated early on, normal embryos can develop
            3. deuterostomes vertebrates
         2. spiral cleavage
            1. irregular clump of cells
            2. determining factors segregate early - mosaic
            3. protostomes

See Figures 7-8 to 7-11.

1. Blastulation
   1. cluster of cells = blastula
   2. often center of fluid = blastocoel
   3. polarity
      1. origin of bilateral symmetry
      2. often determined by point of sperm entry

1. Gastrulation
   1. formation of gut and cell layers
   2. depends on amount of yolk
   3. primitive gut = archenteron
   4. tissue layers
      1. outer = ectoderm
      2. inner = endoderm
      3. middle = mesoderm
2. Origins of tissues

1. Mechanisms of development
   1. nuclear equivalence
      1. all cells have same genetic information
      2. cortex (outer layer of egg) differs
      3. potency may be lost later in development
   2. loss of totipotency
      1. induction
         1. effects of neighboring cells

Reading:

Read through all of Chapter 7; focus on the material related to deuterostomes.

Zoology Home Page

Syllabus

How to Create HTML Documents

Vertebrate Zoology Taxa

Section Notes

Links to sites of Zoological Interest