ZOO501 Official Handouts

ZOO501 - Developmental Biology

Topic.1 INTRODUCTION TO DEVELOPMENTAL BIOLOGY

All multicellular organisms arise by a slow process of progressive change called development. Development is a process by which a multicellular organism arises, initially from a single cellthe fertilized egg, or zygote, which divides mitotically to produce all the cells of the body.

The study of animal development has traditionally been called embryology, from that stage of an organism that exists between fertilization and birth.

Each day we replace more than a gram of skin cells (the older cells being sloughed off as we move), and our bone marrow sustains the development of millions of new red blood cells every minute of our lives.

Fertilization

How gametes fuse with each other

Cell Division

How is cell division regulated?

In addition, some animals can regenerate severed parts, and many species undergo metamorphosis (such as the transformation of a tadpole into a frog, or a caterpillar into a butterfly).

So Developmental biology is a discipline that studies embryonic and other developmental processes.

• How do cells form ordered structures?

Development accomplishes two major objectives:

✓ It generates cellular diversity and order within each generation. ✓ It ensures the continuity of life from one generation to the next.

Topic. 2 DEVELOPMENTAL HIERARCHY OF ANIMALS

The developmental hierarchy is the hierarchical series of decisions involving specific preexisting cell types. These developmental decisions are usually irreversible, that progressively and irreversibly restrict cell fate.

Animal development is the division of embryo into the three germ layers.

1. Ectoderm
2. Mesoderm
3. Endoderm

Potency and cell fate

1. Potency is the entire range of the cell types a particular cell can give rise to in all possible environments.
2. For example: A cell is pluripotent if it can give rise to all different blood cell lineages. There is a decrease in potency as cells become committed.

Fate of a cell is all the different cell types, its descendants can become during normal

➢ Cell potency ≥ fate. ➢ Potency is intrinsic property. ➢ Cell fate is equal to potency plus environment. ➢ Cell fate becomes increasingly restricted until a cell is terminally differentiated.

Topic .3 ANATOMICAL APPROACHES TO DEVELOPMENTAL BIOLOGY

The basis of all research in developmental biology is the changing anatomy of the organism. What parts of the embryo form the heart? How do the tissues that form the bird wing relate to the tissues that form the fish fin or the human hand?

Following important parameters weave together to form the anatomical approaches to

➢ Comparative embryology ➢ Evolutionary embryology ➢ Teratology

➢ Comparative embryology:

The first strand is comparative embryology, the study of how anatomy changes during the development of different organisms. For instance, a comparative embryologist may study which tissues form the nervous system in the fly or in the frog.

➢ Evolutionary embryology:

The second strand, based on the first, is evolutionary embryology, the study of how changes in development may cause evolutionary changes and of how an organism's ancestry may constrain the types of changes that are possible.

➢ Teratology:

The third anatomical approach to developmental biology is teratology, the study of birth defects. These anatomical abnormalities may be caused by mutant genes or by substances in the environment that interfere with development. The study of abnormalities is often used to discover how normal development occurs.