Page 152 - 86 human physiology part-2

Genetics and Inheritance

called gene therapy vectors.

A few of the different viruses used as gene therapy vectors are: Retroviruses - A class of viruses
that can create double-stranded DNA copies of their original RNA genomes. Theses copies of its
genomes can be mixed into the chromosomes of "host" cells. HIV is a type of retrovirus. Adenoviruses
- A class of viruses with double-stranded DNA genome that cause respiratory, intestinal, and eye
infections in humans. The common cold is an adenovirus. Adeno-associated viruses - A class of small,
single-stranded DNA viruses that can insert their genetic material at a specific site on chromosome 19.
(chromosome 19 represents about 2% of the human genome and contains about 1,500 genes. Some of
the genes included are genes that code for insulin-dependent diabetes, myotonic dystrophy, migraines,
and inherited high blood cholesterol). A class of double-stranded DNA viruses that infect a particular
cell type, neurons, called Herpes simplex viruses is another common virus used in gene therapy. It is
the virus that causes cold sores.

Major advancements have been made in gene therapy. There are many new discoveries in helping
cure and treat diseases that claim millions of lives. Some of the disease that have cures or treatments
because of gene therapy include: Parkinson's, Huntington's, Cystic Fibrosis, Some cancers, "Bubble
Boy" syndrome and sickle cell. With technology jumping ahead, maybe someday there will be a cure
for every life threatening disease.

Genetic Regulation of Development and Homeostasis

It is very easy to think of Genetics as why I have blue eyes while both of my parents have brown
eyes. Or how hemophilia is passed down from mother to son, and not mother to daughter. But Genetics
is more in depth than that. At conception you started as a single cell. That cell started to divide. You
didn’t increase in mass just in the number of cells. Once the bundle of cells reached a certain number,
things changed. You started gaining mass by acquiring new resources (from your mother) and
increasing in cell number. Your cells specialized. Some cells became the liver. Others became heart,
lungs, brain, and so forth. Why is this? How did that little bundle of cells "know" when it was time to
specialize? It is because your DNA has regulatory control over your entire system. If it didn’t, that
bundle of cells would just keep dividing as undifferentiated cells and never specialize, never gain form
or function. Thanks to the genetic regulatory control over your system, your anatomy forms correctly
with everything in its proper place. Even after fetal development gene regulation still controls what
each cell produces and how it functions. Puberty just doesn’t happen at the age of twelve. Puberty
happens because genes in your genetic code are triggered by your growth and development, causing
your endocrine system to start producing the proper hormones, thus causing you to mature sexually.

Even aging is genetically controlled. The mechanisms of genetic regulation are not discussed here,
but it is worth noting that any step of gene expression may be modulated, from the DNA-RNA
transcription step to post-translational modification of a protein. Gene regulation gives the cell control
over structure and function, and is the basis for cellular differentiation. A cell can also respond to
changes in its environment by altering gene expression. For example, a pancreatic cell exposed to high
glucose levels releases pre-formed insulin that it was storing. Yet, if the high levels of glucose
continue, the cell will transcribe additional copies of the gene for making insulin and thus increase
insulin production to meet demand. This is homeostasis in action.

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