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I don't know about “opposite” - our chromosomes are almost exactly like those of the Great Apes - our chromosome #2 looks like a fusion of two Ape chromosomes - leading us to have 23 pairs instead of 24 pairs.

The same genes in chromosome #2 are lined up in the same order as in the Ape chromosomes - and there are even telomere sequences in the middle of Chromosome #2 where one would find them at the ends of the Ape chromosomes.

Epigenetics is just another way of regulating genes - it is done through methylation modifications right there on the DNA molecule - not external to it. This modification tends to wrap up a gene that is not going to be used in ‘chromatin’ where it will not be available to RNA polymerase that would express the gene.

For example there is a sequence outside the gene for the lactase enzyme used to digest the milk sugar lactose. In almost all mammals (and most humans) this sequence is epigenetically modified so that after weening from mother's milk - the gene is wrapped up in chromatin and no longer used - making them “lactose intolerant”.

This sequence is mutated in many European populations - and in some African populations that herd cattle - so that the normal epigenetic change doesn't happen and the gene for lactase is expressed throughout life.

What do you mean by “spaces” in DNA?

HOT SPOTS ~ allmendream ~ look at discussions of what are called HOT SPOTS ~ the points where the chromosome from your father hooks up with the same chromosome from your mother.

Humans do it different.

Actually that whole field has gotten rather exciting in recent months after that finding was reported and now you get such incredible articles as the one at "http://genomewiki.ucsc.edu/index.php/PRDM9:_meiosis_and_recombination" which is one of the clearer versions I've seen ~ most these guys can't write of course, but eventually professional science writers will eventually straighten all this out.

Personally I have been amazed mostly with the fact these guys can look at linking processes involving specific sites on DNA.

It has to do with the expected array ~ sometimes something you would think should be there is "deleted" ~ hence they are called "deletions". If critter A needs 10 copies of a specific gene, and critter B has 9 copies at that location on a chromosome, then critter B has a deletion, or maybe critter A has an insertion.

Reversals are fun ~ love reading about them since they are currently under intense study by folks who think schizophrenia and bipolar disorder are mediated by the same area of the same chromosome. I gather reversals have survival value, but why? What is the advantage of schizophrenia to the species?