Unit 1: Introduction to Developmental Biology

Question 1

the first known embryologist

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Aristotle

Question 2

Most multicellular organisms arise by

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sexual reproduction

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Some multicellular organisms are capable of

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asexual reproduction

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Some plants can be propagated through

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Cuttings

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the vast majority of new complex organisms arise from a

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fertilized egg called zygote.

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Multicellular organisms do not spring forth fully formed. Rather, they arise by a relatively slow process of progressive change that we call

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Development

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is the study of animal development, from that stage of an organism that exists between fertilization and birth

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Embryology

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as the discipline that studies embryonic and other developmental processes

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Development Biology

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Development happens most obviously in the course of

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embryonic development or postembryonic life

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is the science that seeks to explain how the structure of organisms changes with time. Also, it is the study of embryonic and other developmental process

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Developmental Biology

Question 11

2 Objectives and Questions of Developmental Biology

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 It generates cellular diversity and order within each (How does the fertilized egg give rise to the adult body?)
 It ensures the continuity of life from one generation to the next (How does that adult body produce yet another body?)

Question 12

Seven (7) General Questions by Developmental Biologist:

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1. The question of differentiation
2. Morphogenesis
3. Growth
4. Reproduction
5. Evolution
6. Environmental Integration
7. Regeneration

Question 13

How can the fertilized egg generate so many different cell types?

 there are more than 200 different specialized cell types in a vertebrate body, ranging from epidermis to thyroid epithelium, lymphocyte, or neuron.
 Each cell owes its special character to particular proteins coded by particular genes,

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The question of differentiation:

Question 14

is the generation of cellular diversity.

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Differentiation

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How can the cells form such ordered structures?

 cell and tissue movements that give the developing organ or organism its shape in three dimensions.
 Depends on the dynamics of the cytoskeleton and on the mechanics and viscoelastic properties of cells.

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The question of morphogenesis:

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is the creation of ordered form.

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Morphogenesis

Question 17

How do our cells know when to stop dividing? How is cell division so tightly regulated?
 Refers to increase of size, and the control of proportion between body parts.
 Although more familiar to the lay person than other aspects of development.
 It is currently the least well understood aspect in terms of molecular mechanism.

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The question of growth:

Question 18

How are these cells set apart to form the next generation, and what are the instructions in the nucleus and cytoplasm that allow them to function this way?
 The sperm and egg are very specialized cells.

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The question of reproduction

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How do changes in development create new body forms? Which heritable changes are possible, given the constraints imposed by the necessity of the organism to survive as it develops?

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The question of evolution:

Question 20

involves inherited changes in development.

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Evolution

Question 21

How is the development of an organism integrated into the larger context of its habitat?
 The development of many organisms is influenced by cues from the environment.

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The question of environmental integration

Question 22

 Some organisms can regenerate every part of their body
 Mammals are generally poor at regeneration, there are some cells in our bodies (stem cells) that are able to form new structures even in adults.

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The question of regeneration

Question 23

The stages of development between fertilization and hatching are collectively called

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embryogenesis.

Question 24

The Cycle of Life: Patterns of embryogenesis are variations on six fundamental processes called:

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1. Fertilization
2. Cleavage
3. Gastrulation
4. Organogenesis
5. Metamorphosis
6. Gametogenesis

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the fusion of the mature sex cells, the sperm and egg, which are collectively called the

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Fertilization and gametes

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series of extremely rapid mitotic divisions that immediately follow fertilization

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Cleavage

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During cleavage, the enormous volume of zygote cytoplasm (hollow ball of cells) is divided into numerous smaller cells called

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blastomeres

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By the end of cleavage, the blastomeres have usually formed a sphere, known as a

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blastula

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the space between the blastomere

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Blastocoel

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a series of extensive cell rearrangements. The embryo contains three germ layers that will interact to generate the organs of the body.

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Gastrulation

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Three germ layers

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Endoderm, Mesoderm, Ectoderm

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Embryo transforms from a one-dimensional layer of epithelial cells and reorganizes into a multilayers and multidimensional structure called

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gastrula

Question 33

the cells interact with one another and rearrange themselves to produce tissues and organs. Certain cells undergo long migrations from their place of origin to their final location.
 Ex. Migration in the precursors of blood cells, lymph cells, pigment cells, and sex cells
 The process of formation of organs from three germ layers.

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Organogenesis

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young organisms is called a (last the longest), and adult is a brief stage whose purpose is to reproduce.
 Change of form or structure in an individual after hatching or birth.

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Metamorphosis and Larva

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the development of gametes; usually not completed until the organism has become physically mature.

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Gametogenesis

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2 type of gametogenesis

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1. Somatic Cell
2. Germ Cell

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(which give rise to the individual body) – the cells in the body other than sperm and egg cells.

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Somatic Cell

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which contribute to the formation of a new generation) – the embryonic precursors of the gametes.

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Germ Cell

Question 37

 In most species of frogs, fertilization is external.
 The male frog grabs female’s back and fertilized the eggs as the female releases them.
 Fertilization accomplishes both sex and reproduction.
 Cleavage: the volume of the frog egg stays the same, but it is divided into tens of thousands of cells
 Blastopore an opening in the blastula

Answer 37

A Frog’s Life Cycle: Gametogenesis & Fertilization

Question 38

 It begins when the cells of the most dorsal region of the mesoderm condense to form a rod of cells (notochord)
 Neurula, neural tube, and somites

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A Frog’s Life Cycle: Organogenesis

Question 39

 Amphibian metamorphosis is initiated by hormones from the tadpole’s thyroid gland.
 The speed of metamorphosis is keyed to environmental pressure.

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A Frog’s Life Cycle: Metamorphosis & Gametogenesis

Question 40

used as an example of how all animals develop.

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Major Model Organisms

Question 41

The Big Six

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1. Mouse
2. Chick
3. Frog
4. Zebrafish
5. Fruit Fly
6. Nematodes

Question 42

How the Big six choose

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1. Availability and Cost
2. Access and micromanipulation
3. They have special properties that allow their mechanisms of development to be easily observed (clear embryos, large cells, etc.).
4. Can be easily manipulated – physically or genetically
5. Have relatively fast development period
6. Genomes have been mapped

Question 43

1. All the big six are available all year round.
2. Easy to obtain thousands of eggs from the first four species
3. Cost: modern research demands a weekly or even daily supply of embryos.

Answer 43

Availability and Cost:

Question 44

1.______refers to how easy it is to get at embryos at all stages of development. (Ex. Xenopus and zebrafish)
2._______ removing a single cell, or a small piece of tissue, grafting an explant to another position in a second embryo, or injecting individual cells with substances.

Answer 44

Access and micromanipulation:
and Microsurgical manipulation