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M14. DNA and protein sequences usually show greater similarity between closely related groups of organisms than between distantly related groups.


Student Outcome: M14.1

Understand that organisms have common features attributable to commonly shared sequences of DNA.


New Genome Comparison Finds Chimps, Humans Very Similar at the DNA Level

WASHINGTON, Wed., Aug. 31, 2005 - The first comprehensive comparison of the genetic blueprints of humans and chimpanzees shows our closest living relatives share perfect identity with 96 percent of our DNA sequence, an international research consortium reported today.


In a paper published in the Sept. 1 issue of the journal Nature, the Chimpanzee Sequencing and Analysis Consortium, which is supported in part by the National Human Genome Research Institute (NHGRI), one of the National Institutes of Health (NIH), describes its landmark analysis comparing the genome of the chimp (Pan troglodytes) with that of human (Homo sapiens).


The consortium found that the chimp and human genomes are very similar and encode very similar proteins. The DNA sequence that can be directly compared between the two genomes is almost 99 percent identical. When DNA insertions and deletions are taken into account, humans and chimps still share 96 percent of their sequence. At the protein level, 29 percent of genes code for the same amino sequences in chimps and humans. In fact, the typical human protein has accumulated just one unique change since chimps and humans diverged from a common ancestor about 6 million years ago.


To put this into perspective, the number of genetic differences between humans and chimps is approximately 60 times less than that seen between human and mouse and about 10 times less than between the mouse and rat. On the other hand, the number of genetic differences between a human and a chimp is about 10 times more than between any two humans.


Source: http://www.genome.gov/15515096


Go here for a very visual demonstration of the similarities of human DNA with other living things.


Here is a video about the differences in the diversity of DNA in humans - long and a struggle to watch at times, but stay with it.




Student Outcome: M14.2

Explain why the greater the similarity there is between the sequences of nucleotides in their DNA, the more likely it is that the separation of two species is recent.


Scientists studying the chemistry of DNA moved even closer to actual sequences. Charles Sibley (left) and Jon Ahlquist pioneered the use of DNA kinetics to investigate evolutionary relationships using a technique called DNA-DNA hybridization (see figure, left). Each DNA molecule is made of two strands of nucleotides. If the strands are heated, they will separate—and as they cool, the attraction of the nucleotides will make them bond back together again. To compare different species, scientists cut the DNA of the species into small segments, separate the strands, and mix the DNA together. When the two species’ DNA bonds together, the match between the two strands will not be perfect since there are genetic differences between the species—and the more imperfect the match, the weaker the bond between the two strands. These weak bonds can be broken with just a little heat, while closer matches require more heat to separate the strands again.


DNA hybridization can measure how similar the DNA of different species is—more similar DNA hybrids “melt” at higher temperatures. When this technique was applied to primate relationships, it suggested that humans and chimpanzees carried DNA more similar to one another’s than to orangutans’ or gorillas’ DNA.

Source: http://evolution.berkeley.edu/evosite/history/genetsims2.shtml


A video comparing human and chimpazee DNA




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