DNA and other Questions

William Tivol tivol at news.wadsworth.org
Fri Jul 28 16:54:35 EST 1995


Dear Tyla,

tyla stiles (maggie at ix.netcom.com) wrote:
: 1.  Is the DNA found in all of your cells both somatic and sex cells
: the same within one individual? 

	The DNA in sperm and egg cells is haploid--i.e. only one of each chro-
mosome--whereas the DNA in somatic cells is diploid--two chromosomes, one from
each parent.  There are processes of somatic mutation which affect somatic
cells and their offspring, so not all the somatic cells have the same DNA, but
they all have *nearly* the same DNA, since somatic mutation affects only a
small portion of the DNA in any one cell.  These somatic mutations are not
passed along to your children, instead, they are responsible for such proces-
ses as cancer (when a mutation affects the control of cell division) and the
immune response (when the stem cells are processed by the thymus, and only
those which have mutated will survive--see articles by N. K. Jerne).  But ex-
cept for special processes and accidents, an individual's cells have the same
DNA.

: 2.  How does DNA differ from one individual to the next (through
: differences in base pairing?)?   

	DNA differs in its sequence.  Two individuals (except for homozygotic
twins, clones, etc.) will have different sequences in their DNAs, but the
overall organization of the DNA is very similar in individuals of the same
species.  Thus, when the parental, haploid chromosomes combine, blocks of DNA
will be the same or similar.  Thus, the genes for, say, eye color are on cor-
responding chromosomes, and in about the same location on each chromosome
(there may be some small variation due to the length variation found in some
alleles [an allele is a possible example of a particular gene, such as that
responsible for brown eye color, or that for blue eye color]).  The normal
base pairing, A-T and C-G, is the same in all individuals (there are examples
of abberent base pairing, which is one mechanism of mutation).

: 3.  What is the Human Genome Project?  Which individual's DNA is being
: used in this project?

	HUGO is a project to characterize all the (typical) human genome as to
the location of each coding region (gene), functional but non-coding DNA, such
as promoter regions etc., structural regions, which serve to allow the confor-
mation of DNA to be appropriate for replication, transcription, etc., and re-
gions with no apparent function (so-called "junk DNA").  There are several in-
dividuals whose DNA is being analysed for HUGO, so the final result will not
represent any individual's DNA.  However, I believe, all the donors are white,
so the DNA may not be entirely representative.  Since all humans are the same
species, the lack of inclusion of other races (chromosomes of color? ;-)) is
not thought to be a serious flaw--some alleles may be missed, but not likely
any genes.  I hope this helps.
				Yours,
				Bill Tivol




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