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         For many years I have been interested in the history of my family.  The advent of computers has sped up this process and recently a new tool has been added to the process–DNA analysis.  

           Recently when I was in Texas, I noticed that the genealogy web site, Ancestry.com, had a half price sale on their DNA tests.  I had been wanting to perform these tests for a long while but was unwilling to shell out the big money to do it.   I broke down and ordered the tests–the Y chromosome and mitochondrial DNA test for me and the mitochondrial DNA test for my father.

          There are several other companies that offer the most common tests being done at this time–the Y chromosome test and the mitochondrial DNA test.  The Y chromosome is of course the chromosome that determines maleness.  Males have the X and Y sex chromosomes, whereas females have two X chromosomes (XX).    During the formation of the eggs and sperm (meiosis),  all the so called homologous chromosomes which contain the same basic type of DNA, pair up and often exchange segments of their DNA (crossing over).  This results in the changing of the base sequence which is the genetic code. 

          The Y chromosome is a small chromosome and crossing over with the X chromosome normally doesn’t occur as often as it does with the other pairs of chromosomes (Check out my entry on June 21, 2007 for more information on the Y chromosome).  As a consequence the sequence of bases on its DNA doesn’t change around as much as other chromosomes.  Any changes in the base sequence usually comes about by mutations, or small changes in the base sequence.

          The rate of this mutational change can be estimated, and since the genetic code on the Y chromosome is not as subject to natural selection as is the code on the other chromosomes (autosomes), this mutation rate can be used to estimate how long ago a change occurred when comparing the Y chromosomes of two different men.  Also the Y chromosomes can be compared to see how closely related two men are.

          The mitochondrial DNA (mDNA) is a whole ‘nother creature.  Whereas the nuclear DNA is passed from one generation to the next via the eggs and sperm (gametes) and controls the various genetic traits through the synthesis of enzymes, the mitochondrial DNA is not found in the nuclear chromosomes but in the mitochondria which is a small structure (organelle) in the cell which is responsible for the aerobic reactions of cell respiration–combining food with oxygen to produce lots of energy.

          The mitochondria has a fascinating history, and is believed to be a once free living bacteria, partly based on it’s loop-shaped chromosomes, as opposed to the rod-shaped chromosomes found in us and other Eukaryotic creatues.  Check out the endosymbiotic theory when you have time.

         Once again, like the Y chromosome, the DNA in the mitochondria is not that subject to the influence of natural selection and it does not go through a shuffling process (independent assortment) or crossing over as the nuclear chromosomes do, thus it will not change unless a random mutation occurs.  Apparently the mutation rates in mDNA is higher than the nuclear DNA which makes it useful in comparing lineages.

       The Y chromosome is passed from father to son and can be used to determine information about a male’s paternal ancestry.  The mDNA is found only in the area outside of the nucleus, thus sperm can not pass on mitochondria from the father since only the head of the sperm (containing half the normal number of chromosomes) enters the egg at fertilization.

       The egg (oogonium), on the other hand being a large cell, contains mitochondria which are passed on to the cells of the resulting children after fertilization.  Thus the mDNA is only passed from mother to offspring of both sexes.  Therefore, the mDNA is useful for determining information on the maternal ancestry of a person.

          I am now receiving the information on these tests and will in the coming days talk about the results.

  I couldn’t resist including this model of DNA copied from Wikipedia