The "rough draft" of the 3 billion base pair sequence of the human genome was completed a few years ago, and the publications of the "final version" analyses of the individual chromosomes have been appearing over the past two years ( as we saw for the X chromosome a few weeks ago). Just last month, the complete genome sequencing and analysis of the chimpanzee was published. So, how does the human genome compare to that of our nearest evolutionary relative?
1. What is a concise summary of the overall characteristics of the human genome?
a. The human genome is about 90% euchromatic, about 10% heterochromatic.
b. About 30% of the genome is transcribed, but only 1 to 2% is translated ("coding regions within genes").
c. A bit over half of our DNA consists of repeated sequences of various types, with telomeres and centromeres (in particular) containing large segments of repeated DNA sequences.
d.. We have about 25,000 genes, with about 10% of these being specific to vertebrates.
e. At the molecular level, the biggest difference between us and flies is the greater complexity of our proteins; many of our proteins have more domains and novel combinations of domains. Individual domains of proteins are often coded by individual exons (or combinations of exons) within genes.
f. Individual humans differ from one another by about one base pair per thousand. So, for two unrelated individuals of the same gender, there are about 6 million base pair differences, "single nucleotide polymorphisms ( SNPs )", which can in principle be used as markers in DNA analysis.
2. How does the human genome compare to that of our nearest evolutionary relatives?
The analysis of the chimpanzee genome was published just one month ago in the journal Nature, and highlighted as "news of the week" in the journal Science. Here are the links to the publication in Nature and the news article in Science
Nature, "Initial sequence of the chimpanzee genome and comparison with the human genome". Print this abstract page, then click on "full text" to see the entire publication. Scan through and look briefly at the figures and tables.
Science, "Chimp genome catalogs differences with humans". Print and read this brief article. Answer the following questions from this article. (You must access the Science website through a Lehigh connection, so the journal's website "sees" the request coming from Lehigh, which has a full access subscription.)
1. On average, for a specific human protein and its equivalent chimp protein, how much of the amino acid sequence is different? ______ amino acids out of the average total of _______ amino acids (from Problem S-1).
2. Among all the proteins made by each species, what percentage are identical in humans and chimps? _____%
3. The genome size for both humans and chimps is about 3 billion base pairs. The total number of "single base substitutions" (same thing as SNPs) between the two species is about ______________; so "only ______% of nucleotide bases differ between chimps and humans".
4. Duplications of sequence ( insertions) and deletions contribute more genetic difference than SNPs between the two species; there are about __________ insertions and deletions, accounting for a difference of about ______________ base pairs. In percentage terms, this is about _______%.
5. Comparison of the human and chimp data allowed researchers to identify _______ genes that are evolving more quickly in people, including genes involved in defense against ____________ and ____________.
6. One gene present in both species, but for which the alleles found in humans differ noticeably from the alleles found in chimps, is the _______ gene, proposed to be important in the evolution of speech. The locus of this gene is in a region of the genome that may have been involved in a "___________ ___________" sometime during human history.
7. "Overall, however, the vast majority of (genetic) changes between humans and chimps appear to be __________".