BioG 1105-1106 at Cornell University
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Unit 3: Demos

Objective 3:

Operon Tutorial
lac operon animation
Induction of the lac operon

Objectives 4 & 5:

Positive v. negative control of prokaryotic gene transcription

Objective 6:

Transcription of eukaryotic vs. prokaryotic genomes (6c)

Objective 7:

How Does Methylation Control Synthesis of Proteins?
You are what your grandmother ate - diet linked to methylation (optional)
Genetic Imprinting: The Battle of the Sexes - Reloaded (optional)
Genome biology: She moves in mysterious ways - The human X chromosome is a study in contradictions. The detailed sequence of the X, and a survey of inactivated genes in females, help to illuminate this unique 'evolutionary space'.
Unexpressed but Indispensable: The (non-coding) DNA Sequences that Control Development. (optional)

Objective 9:

optional:

Diagram showing how Dolly was made (from Liem et al. Functional Anatomy of the Vertebrates, 3rd ed.)
Give the dog a clone
ViaGen: Gene Banking and Cloning of Exceptional Pets

Objective 14:

Yolk content and cleavage in human eggs (14c)
Zygote and morula (14d):
Zygotes: sea urchin, frog (zygote upper left, morula bottom right)

Objective 16:

Notochord development (16a)
Neural crest cells (16d):
Formation and fate of neural crest cells (16d)
Scientists Hatch a Few Odd Birds  (optional)
Somite development (16e)

Objective 17:

Comparative development (17b)

Objectives 19 & 20:

Determinate v. indeterminate cleavage & embryonic induction

Slides

Unit 3 Slides (accompanying text can be found in your Survival Manual on pages 57-59.)

Neural Crest Cells

Although derived from ectoderm, the neural crest has sometimes been called the “fourth germ layer” because of its importance. Neural crest cells have also been considered the developmental factors (along with input from Hox genes) that “make humans human” because of their role in determining facial structure.

Neural crest cells are unique to vertebrates and give rise to a variety of important structures in the adult body. Their name suggests their origin. As neurulation proceeds and the neural tube begins to form, neural crest cells are groups of cells positioned on the top (dorsal) edges of the forming neural folds (see diagram below). Once the neural tube has formed and invaginated, the neural crest cells form a distinct population of cells resting on top of (just dorsal to) the neural tube. These cells will migrate away along defined routes to a number of locations as development proceeds.

In the end, neural crest cells form a wide array of different cell types including skin pigment cells (melanocytes and others), neurons of the dorsal root ganglia of spinal nerves, the autonomic nervous system (both sympathetic and parasympathetic ganglia - think about the paths these nerves take from the spinal cord to their target organs? These paths are formed during the initial migration of the neural crest cells away from the nerve tube), Schwann cells responsible for myelination of peripheral nerves, and the adrenal medulla - which is so intimately connected to the sympathetic nervous system via hormonal signaling with epinephrine and norepinephrine. Neural crest cells are also important in the head - forming some bones and cartilage in the lower jaw as well as portions of the eyes, ears, and teeth.

Neural crest cells. Successive stages of amphibian neurulation diagrammed in transverse sections. Each of the drawings shows the neural ectoderm, the epidermal ectoderm, and the neural crest. When the neural folds fuse, they close the neural tube under a continuous layer of epidermis. The cells originally located at the crests of the neural folds, known as neural crest cells, then come to lie on top of the neural tube, from where they migrate to different locations and have a wide variety of fates. Figure 13.22 from K. Kalthoff. 2001. Analysis of Biological Development. McGraw Hill, Boston.

Fig. 34.7 from Campbell 7th Edition

 

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