Try this:
This is a pretty good article from Science.
Volume 281, Number 5382 Issue of 4 Sep 1998, pp. 1432 - 1434 The American Association for the Advancement of Science
For the moment, no one can tie the few known molecular variations with the familiar litany of chimp-human differences, such as body hair, language,or brain size.
“This is one of the major questions that those of us interested in our own biology would like to ask–what does that 1.5% difference look like?” says Francis Collins, director of the National Human Genome Research Institute.
"That question was first raised in print in a landmark 1975 paper by geneticist Mary-Claire King and the late biochemist Allan Wilson, both then of the University of California, Berkeley. They surveyed protein and nucleic acid studies and found that the average human protein was more than 99% identical to its chimpanzee counterpart; the coarse DNA hybridization methods of the time showed that the average nucleic acid sequence was almost as similar (Science, 11 April 1975, p. 107).
"Thus, King and Wilson concluded, humans
and chimpanzees were genetically as similar as sibling species of other organisms, such as fruit flies or mice.
"This left a great paradox: Our DNA is almost identical to that of our chimp cousins, but we don’t look or act alike. “The molecular similarity between chimpanzees and humans is extraordinary because they differ far more than many other sibling species in anatomy and way of life,” the pair wrote.
"What’s more, much of the DNA in any organism is so-called “junk DNA” that has no apparent function, and mutations in these regions do not change the function of genes. Thus, many of the genetic differences between humans and chimps probably don’t affect the organisms at all. (I thought someone just came up with a good understanding of “Junk DNA” but I can’t remember it right now.)
"The challenge is to find those few mutations that do make a difference–either by altering genes that code for proteins or by changing how genes are regulated, King and Wilson said.
"But although many labs have since confirmed that our nuclear DNA is 98% to 99% identical to that of chimpanzees, few have taken on the quest to find the differences that matter. “It was one of those fields that fell through
the cracks,” says Ajit Varki, a glycobiologist at the University of
California, San Diego (UCSD), who has recently surveyed the known differences between humans and apes.
“What’s different? What makes us human?”
"One way to answer that question is to start with biochemical differences, and then trace them back to their genetic origins. That approach has yielded its first big payoff, to be reported in the October issue of the American Journal of Physical Anthropology.
After studying tissues and blood samples from
the great apes and 60 humans from diverse ethnic groups, Varki and his colleagues Elaine Muchmore and Sandra Diaz at UCSD were surprised to find that human cells are missing a particular form of sialic acid, a type of sugar, found in all other mammals studied so far, including the great apes.
“Now you’ve got something that is changing the surfaces of all cells in the body,” says Varki.
"…There are even hints that sialic acid may
be involved in cellular communication during brain development and function, says Varki.
"…But the human form is simply the basic acid, lacking the additional oxygen atom. That changes the shape of the molecule in a region that could alter how it is recognized by other molecules, whether pathogens or cellular messengers, says Varki.
"Yet the question still remains: Does this biochemical difference matter? No one has yet identified a specific function altered by the loss of this particular version of the molecule.
"But others, such as Pääbo, think that chromosomal rearrangements at influential sites are rare and so are skeptical that they play a major role in the differences between chimp and human.
"Pääbo and King think instead that the most promising research avenue is to identify small sequence differences that subtly change the expression of genes that regulate the timing of development, such as those that code for transcription factors that might lengthen the growth period of the brain and, hence, allow more complex brain structure in human fetuses.
"Pääbo’s group in Munich and Leipzig has sequenced a 10,156-base pair segment of DNA in the X chromosome of humans and chimpanzees, confirming again that they are about 99% similar. Now they’re seeking differences in the expression of the identified genes in the brain and in the immune system.
"And at GenoPlex Inc., a Denver-based company founded last year by University of Colorado Health Sciences Center geneticists Jim Sikela and Tom Johnson, researchers have come up with a rapid method to find meaningful
sequencing differences between humans and chimps. After sequencing a stretch of DNA in each species, they count two different types of nucleotide differences: those that change the structure and function of a protein product, and silent substitutions that don’t.
"If the ratio of replacement to silent
substitutions is high, they consider that the gene sequence is likely to have undergone
a functional change that was selected for in humans.
“Preliminary results suggest that they have found uniquely human genes involved in AIDS susceptibility and learning and memory, says Walter Messier, an evolutionary biologist at the company. The firm has submitted patents on novel uses of these gene sequences, which they hope may become targets for drugs.”
Note: I added more paragraphing and have greatly condensed this article.
Additionally: That extra chromosome is not DNA no one has ever seen before. They can
tell from the gross structure of it (in karyotype -like assays) that it’s made up of bits of rearranged dna that can be found in the 23 chromosomes … it’s sort of a piece that came off and ended up as a chromosome.
Presented at a…thesis defense.
Oh, I’m gonna keep using these #%@&* codes 'til I get 'em right.