Why is RNA necessary to act as a messenger? Why can't the code be taken directly from the DNA? How do some cells become brain cells and others become skin cells, when the DNA in ALL the cells is exactly the same? In other words, if the instructions are exactly the same, how does one cell become a brain cell and another a skin cell?

In the process of mitosis that starts from zygote, how dodifferent cells appear? What happens that some cells become onetype and some another?

For example, is there a cell that divides into a blood cell anda skin cell?

What makes a skin cell different from a brain cell?

A) Skin cells are haploid, and brain cells are diploid.

B) The skin cell expresses different genes compared to the brain cell.

C) The skin cell is missing brain-specific genes.

D) There are brain specific chromosomes that are missing in the skin cell.

E) Skin cell chromosomes undergo crossing over to shut off brain genes.

1. Read the article "Stem Cells Used in Landmark Therapy forFailing Sight".http://www.newscientist.com/article/dn26220-stem-cells-used-in-landmark-therapy-for-failing-sight.html#.VHYmRcnt9z8

2. In the article, scientists turned skin cells intoundifferentiated stem cells (call iPS cells) and then turned theundifferentiated stem cells into eye cells. Use your model toexplain what would have to happen for a skin cell to become anundifferentiated stem cell and then what would need to happen forthe undifferentiated stem cell to become an eye cell.

3. Your friend claims that eye cells and skin cell containdifferent genes (i.e. have different DNA sequences). Does theconversion of skin cells to stem cells to eye cells support orrefute your friend's claim? Explain, at the molecular level, howthis evidence supports or refutes the claim.