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Photo shows an agarose gel illuminated under UV light. The gel is nine lanes across. Each lane was loaded with a sample containing DNA fragments of differing size that have separated as they travel through the gel, from top to bottom. The DNA appears as thin, white bands on a black background. Lanes one and nine contain many bands from a DNA standard. These bands are closely spaced toward the top, and spaced farther apart further down the gel. Lanes two through eight contain one or two bands each. Some of these bands are identical in size and run the same distance into the gel. Others run a slightly different distance, indicating a small difference in size.
DNA can be separated on the basis of size using gel electrophoresis. (credit: James Jacob, Tompkins Cortland Community College)

Evolution connection

The first draft sequence of the Neanderthal genome was recently published by Richard E. Green et al. in 2010.

Richard E. Green et al., “A Draft Sequence of the Neandertal Genome,” Science 328 (2010): 710-22.

Neanderthals are the closest ancestors of present-day humans. They were known to have lived in Europe and Western Asia before they disappeared from fossil records approximately 30,000 years ago. Green’s team studied almost 40,000-year-old fossil remains that were selected from sites across the world. Extremely sophisticated means of sample preparation and DNA sequencing were employed because of the fragile nature of the bones and heavy microbial contamination. In their study, the scientists were able to sequence some four billion base pairs. The Neanderthal sequence was compared with that of present-day humans from across the world. After comparing the sequences, the researchers found that the Neanderthal genome had 2 to 3 percent greater similarity to people living outside Africa than to people in Africa. While current theories have suggested that all present-day humans can be traced to a small ancestral population in Africa, the data from the Neanderthal genome may contradict this view. Green and his colleagues also discovered DNA segments among people in Europe and Asia that are more similar to Neanderthal sequences than to other contemporary human sequences. Another interesting observation was that Neanderthals are as closely related to people from Papua New Guinea as to those from China or France. This is surprising because Neanderthal fossil remains have been located only in Europe and West Asia. Most likely, genetic exchange took place between Neanderthals and modern humans as modern humans emerged out of Africa, before the divergence of Europeans, East Asians, and Papua New Guineans.

Several genes seem to have undergone changes from Neanderthals during the evolution of present-day humans. These genes are involved in cranial structure, metabolism, skin morphology, and cognitive development. One of the genes that is of particular interest is RUNX2 , which is different in modern day humans and Neanderthals. This gene is responsible for the prominent frontal bone, bell-shaped rib cage, and dental differences seen in Neanderthals. It is speculated that an evolutionary change in RUNX2 was important in the origin of modern-day humans, and this affected the cranium and the upper body.

Watch Svante Pääbo’s talk explaining the Neanderthal genome research at the 2011 annual TED (Technology, Entertainment, Design) conference.

Dna packaging in cells

When comparing prokaryotic cells to eukaryotic cells, prokaryotes are much simpler than eukaryotes in many of their features ( [link] ). Most prokaryotes contain a single, circular chromosome that is found in an area of the cytoplasm called the nucleoid.

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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