Re: Why are stable karyotypes important in therapeutic cloning?

By a stable karyotype, I am assuming that you mean there are no observable
major genetic lesions such as nondisjunctions, chromosomal breakage,
chromosomal duplications, ect.  If any stem cell line is going to be used
for therapeutic purposes, you want to make sure that you have not generated
abnormal cell lines while growing them in Vitro. When cells are maintained
for extended periods of time and allowed to grow and divide for many
generations, mutations will accumulate, and eventually, you will begin
selecting for cells that have adapted best to the new in vitro conditions.
These cells typically have higher growth rates and survival mechanisms that
were not present in the cells from which they were originally derived.
Mutation is inevitable, and therefore variation for cell to cell will be
inevitable. If these cells are going to be used for theraputic purposes,
i.e. be used for the production of new tissues, you would want to make sure
that they are derived from stem cells that have no major genetic lesions,
which can be seen by karyotype.
Karyotypiing, however, is only useful for major lesions, and smaller
mutations in isolated genes, or isolated gene amplifications/deletions
would not be detected. So, if a stem cell has been cultured in Vitro for
too long, other tests to ensure that the cells are behaving normally would
be necessary.