Question

1. What is meant by genomic equivalence?

Explain an experiment that supports genomic equivalence by providing functional evidence (Hint: think about what is meant by functional evidence or producing dolly the sheep vs. descriptive evidence like labeling a chromosome and determining different cells in an organisms all have the same chromosome structure). Describe the hypothesis, brief methods, results and conclusion reached.

1. What is the overall message of von Baer’s Laws?

2. Why do you think Darwin was intrigued by these laws (hint: think in terms of continuity and evolution)?

2. During the earliest phases of nervous system development, morphological changes occur and result in the formation of a neural tube.

1. What is the molecular mechanism by which the neural tube physically separates from the epidermis? (Hint: think about differential cell-cell adhesion)

2. Define a “lose it” or loss-of-function technique that would allow you to support that the molecular mechanism above occurs.

3. Describe what is meant by epithelial to mesenchymal transition.

4. During early syncytial specification in Drosophila, bicoid  mRNA localizes to the anterior end of the embryo, where it generates a concentration gradient of the Bicoid morphogen responsible for the development of the head. You perform a chromatin IP experiment to identify new genes that are regulated by the Bicoid transcription factor. You discover Bicoid binds very strongly to the regulatory DNA of a kinase, gene H. It is your job to design a series of experiments to determine if gene H actually functions during head formation of Drosophila.

Briefly describe a strategy for each of the following scientific approaches: (i) find it, (ii) lose it, and (ii) move it (that is, (i) correlation, (ii) requirement, and (iii), sufficiency).

5. It is known that specific signaling pathways promote the development of dorsal structures like the brain and spinal cord. A mutation was discovered in zebrafish that resulted in the duplication of the dorsal side of the embryo (i.e. two heads/brains and spinal cords fused with a shared ventral belly). The loss of function mutation was mapped to the gene Axin, that is, Axin gene function is reduced or removed entirely from the embryo.

1. Which signaling pathway would be affected by the Axin mutation?

2. What is likely to be the effect on Axin loss-of-function on the above signaling pathway (increased or decreased signaling)?

3. Using a reporter gene, how would you test the effect of the axin mutation on the above signaling pathway?

6. Ectopic expression of a gene is forced expression outside of the genes normal domain. In Drosophila, the Gal4 system is used to ectopically express genes in specific places and times.

1. Describe a strategy using the Gal4 system in Drosophila to generate an additional set of eyes in place of the antenna (Hint: think in terms of the ectopic expression an eye master regulator in the antenna domain).  

                     

2. Considering the stages of cell commitment, how might you characterize a cell that initially moves towards an antenna cell fate but then becomes persuaded to be an eye cell? (Hint: think of the environment created by the Gal4 expression system and whether this translates to a neutral or non-neutral developmental context).

7. Dnmts are methyltransferases that function by adding a methyl group to the cytosine of DNA.

1. Describe the importance of DNA methylation to cell identity. How does cell identity play a role in development and maintenance of a tissue?  

2. Explain the connection between DNA methyl and histone methylation?

1. What is an organoid and why are they useful to understanding human development and disease.

2. Briefly describe a strategy where you would use a patient-specific organoid to attempt to understand and cure a disease that you are most interested? (Hint: first think about the disease, then harvesting cells, then creating a useful type of organoid from iPS cells).

1. Describe the mechanism of syncytial specification.  

2. How is it possible that a morphogen gradient of a protein transcription factor can transmit a signal inside the cells of a syncytial embryo?

3. How do morphogen gradients come together to specify regions of the syncytial embryo? (Hint: think about levels of morphogens).

1. What is a stem cell niche? How does a stem cell niche regulate stem cell function?

2. Describe one example of a stem cell niche.

1. What human cell types are pluripotent?

2. Why does harvesting the above pluripotent cells create a moral dilemma?

3. What can be done in the lab to avoid the above moral complications?

Answer 1

Genomic equivalence is the changing of cells phenotypically but without changing genotypically. Genomic equivalence means all cells of an organism may have equivalent genetic information. The number varies with the genome size of an organism.

Ian Wilmut, a biologist had proved that a sheep was cloned from an adult female sheep. In order to prove this, Wilmut and his colleagues had taken cells from the mammary gland of an adult pregnant ewe for culture. The nuclei of the cells were kept at the resting stage of the cell cycle in the medium, and later they found oocytes from a different strain of sheep. The donor cell and the enucleated oocyte were fused by putting them together and passing electrical pulses. Due to this electric pulses, the cell membranes become destabilised making the cells to fuse. On the other hand the same pulses can also activated the egg for development. The embryos formed were then transferred into the uteri of pregnant sheep. So, Dolly (the adult sheep) was derived from the fusion of a mammary gland cell nucleus and an oocyte. Therefore, the nuclei of adult somatic cells became totipotent.

Von Baer’s Laws states that the development of an organism starts from normal to the special, and embryos from different classes are similar at the early stages but they become different as development proceeds. Von Baer had proposed four rules and they are as follows.

1. In embryo more traits of large group was shown earlier than the special character.

2. The less general are formed from the more general forms, and it continues till most special form.

3.  Embryo of a given form becomes separated without passing the other forms.

4. The embryo of a higher form are not similar to any other form except its embryo.