Lec. 24: Genetic Basis of Development

Question 1

Concepts:
1. In embryonic development, cells go through a program of (blank)
2. The fate of cells in the embryo is determined by (blank)
3. Cleavage generates lots of (blank)
4. Cleavage is followed by (blank and definition)

Answer 1

1. In embryonic development, cells go through a program of differentiation and then morphogenesis
2. The fate of cells in the embryo is determined by cytoplasmic determinants
3. Cleavage generates lots of small undifferentiated cells
4. Cleavage is followed by gastrulation, which organises these cells into 3 germs layers - ectoderm, endoderm, mesoderm

Question 2

Embryonic Development

Answer 2

A single celled zygote gives rise to cells of many different cells, each with a different structure and corresponding function

Cell types organized successfully into tissues, organs, organ systems, and the whole organism

Question 3

Cell differentiation

Answer 3

the process by which cells become specialized in structure and function

Question 4

Cytoplasmic determinants

Answer 4

Maternal mRNA and protein distributed unevenly in the egg that influence early development. As a zygote divides by mitosis, cells contain different determinants which lead to different gene expression

Act as transcription factors to turn on specific genes

Question 5

Inductive Signals

Answer 5

Signal molecules from embryonic cells cause transcriptional changes in nearby, adjacent target cells inducing differentiation of specialized cell types (influencing gene expression)

Inductive signals work with cytoplasmic determinants with embryonic development

Question 6

Determination and differentiation

Answer 6

Determination commits a cell to its final fate and after is cell differentiation is the production of tissue specific proteins

Differentiation happens during embryonic development

Question 7

Myoblasts

Answer 7

Produce muscle specific proteins and form skeletal muscle cells

Question 8

MyoD

Answer 8

One of several “master regulatory genes” that produce proteins that commit the cell to become skeletal muscle
MyoD transcription factor binds to the MyoD gene to create MyoD and other mRNA to make a different transcription factor that will help make myosin, muscle proteins, and proteins that block cell cycle

MyoD PROTEIN is a transcription factor

Question 9

Pattern Formation

Answer 9

The development of a spatial organization of tissues and organs (beginning with establishment of major axis in animals)

Question 10

How is the body of a drosophila determined as an embryo?

Answer 10

cytoplasmic determinants in unfertilized egg determine the axes before fertilization. After fertilization, the embryo develops into a segmented larva with three larva stages giving the body plan of an adult
1. Developing egg
2. Mature, unfertilized egg
3. Fertilized egg
4. Segmented embryo
5. Larva

Question 11

Bicoid
What is morphogen gradient hypothesis?

Answer 11

“A morphogen determining head structures”
- Maternal affect gene that affects the front half of the body
- mother’s biocoid gene is concentrated at future anterior (head)
- Morphogen gradient hypothesis- morphogens (gradients of stubstances) establish embryoy’s axes and other features

Question 12

Why is bicoid research important

Answer 12

1. It identified a specific protein required for some early steps in pattern formation
2. It increased the understanding of mother’s role in embryo development (mother produces bicoid MRNA in egg)
3. Demonstrated key developmental principle that a gradient of molecules can determine polarity and position in embryo

Question 13

Cleavage

Answer 13

rapid cell divisions without substantial growth in size to generate a MULTICELLULAR EMBRYO
- Cleavage seperates the cytoplasm of one large cell to many smaller called blastomeres
- The ball of cells is the bastula
- Fluid filled cavity (inside blastula) is blastocoel

Question 14

What influences Cleavage patterns?

Answer 14

Distribution of yolk influences pattern of cleavage
- Vegetal pole has more yolk and animal pole has less yolk
- Difference in yolk distribution results in different looking hemispheres
- Cleavage is completed when ratio of material in nucleus relative to cytoplasm is sufficiently large

First 2 cleavage=4 equal sized blastomeres, 3rd cleavage= assymetric, unequal sized blastomeres

Question 15

Morphogenesis

Answer 15

the process by which cells occupy their appropriate locations and give an organism its shape and involves
1. gastrulation: movement of cells from blastula surface to interior of embryo
2. Organogenesis- formation of organs

Question 16

Gastrulation

Answer 16

1. Begins when a group of cells on the back of blastula moves around surface and begins to invaginate inside embryo at dorsal lip and fill interior
2. Blastocoel begins to shrink as cells move from outside to inside and form archenteron
3. Cells continue to move from embryo surface into embryo by involution (Cells inside called endoderm and mesoderm and cells on surface form ectoderm are fully formed)

In

Question 17

What are the germ layers in frogs and what do they consist of?

Answer 17

1. Ectoderm (epidermis of skin, sweat glands, hair, nervous and sensory systems, pituitary gland, medulla, jaws and teeth)
2. Mesoderm (skeletal and muscular systems, circulatory and lympathic systems, excretory and reproductive systems, dermis, adrenal cortex)
3. Endoderm (epithelial lining of digestive tract and organs, respritaory, excretory, reproductivee, thymus, thryoid)

Question 18

Organogenesis

Answer 18

• Various regions of germ layers develop into organs
• Notochord froms from mesoderm and neural plate from ectoderm early in vertebrae organogenesis
• Neural plate curves inward forming neural tube (neural tube becomes CNS)
• Neural crest cells develop along neural tube of vertebraes and form parts of embryo