Eukaryotes Genomes - PAN TROGLODYTES

The chimpanzee has a thickset body with long arms, short legs and no tail. Much of the body is covered with long black hair, but the face, ears, fingers and toes are bare. They have hands that can grip firmly, allowing them to pick up objects. Noisy and curious, intelligent and social, the chimpanzee is the mammal most like a human.

Chimps are mainly found in rain forests and wet savannas. While they spend equal time on land and in trees, they do most of their feeding and sleeping in trees. Distribution is across the forest zone of Africa from Guinea to western Tanzania and Uganda. In East Africa the chimpanzee is found in the wild in Tanzania and Uganda, but only in captivity in Kenya. Gombe National Park in Tanzania is the first park in Africa specifically created for chimpanzees.

Chimps live in groups called troops, of some 30 to 80 individuals. These large groups are made up of smaller, very flexible groups of just a few animals, perhaps all females, all males or a mixed group. Chimps are agile climbers, building nests high up in trees to rest in during midday and sleep in at night. They construct new nests in minutes by bending branches, intertwining them to form a platform and lining the edges with twigs. In some areas chimps make nests on the ground. They are quadrupedal, walking quickly on all fours with the fingers half-flexed to support the weight of the forequarters on the knuckles. They occasionally walk erect for short distances.

Chimps are diurnal (but often active on moonlit nights) and begin their activities at dawn, their principal diet is leaves, buds and blossoms. They usually pick fruit with their hands, but they eat berries and seeds directly off the stem with their lips. Their diet consists of up to 80 different plant foods.

The female chimp has an estrus cycle of about 34 to 35 days. While in heat, the bare skin on her bottom becomes pink and swollen, and she may mate with several males. She normally gives birth to just one baby, which clings tightly to her breast and, like a human baby, develops rather slowly. An infant can sit up at 5 months and stand with support at 6 months. It is still suckled and sleeps with its mother until about 3 years of age, finally becoming independent and separating from her at about 4 years. Sexual maturity is reached between 8 and 10 years.

Chimps are among the noisiest of all wild animals and use a complicated system of sounds to communicate with each other.

Chimps touch each other a great deal and may kiss when they meet. They also hold hands and groom each other. An adult chimp often has a special "friend" or companion with which it spends a lot of time. Female chimps give their young a great deal of attention. Older chimps in the group are usually quite patient with energetic youngsters.

The number of chimps in the wild is steadily decreasing. The wilderness areas necessary to their survival are disappearing at an alarming rate as more forests are cut down for farming and other activities. As the human's closest relative the chimp is vulnerable to many of the same diseases, and their capture for medical research contributes to their decline. In addition, outbreaks of the incurable disease Ebola hemorrhagic fever, threatens to decimate important chimpanzee populations in the Republic of Congo and Gabon.

Humans and chimps shared a joint ancestor as recently as five million years ago. Biologists have long supposed that if they could identify the genes that changed in the evolutionary lineage leading from the joint ancestor to people, they would understand the genetic basis of how people differ from chimps and, hence, the essence of what makes humans human. Now that the complete genome sequences for both are available, comparing the human and chimp genomes may provide insights into medical conditions that affect humans and not chimps.

Analysis shows that some critical changes happened relatively quickly, over the last 100,000 years. The researchers cite several changes, possibly related to differing life styles, as being especially significant in tipping us toward the "human" end of the primate spectrum. The study highlights differences related to one of humankind's defining qualities-the ability to understand language and to communicate through speech.

However the process of transforming the joint human-chimp ancestor, who was probably a very chimpanzee like creature, into a human seems much more complicated in light of the new analysis. In a preliminary comparisons, scientists have found that a large number of genes shows signs of accelerated evolution in the human lineage. Those are genes that, by a statistical test applied to changes in their DNA, appear to be under strong recent pressure of natural selection and so are likely to be those that make humans differ from chimpanzees. A prominent set of accelerated human genes are those involved in hearing, particularly the gene that makes a protein called alpha-tectorin, a component of the tectorial membrane of the inner ear. It is suggested that the genes governing speech and hearing are most likely to have evolved in parallel and that evolutionary tweaks in the alpha-tectorin gene may make humans hear somewhat differently from chimps. Another group of selected genes is involved in brain development. Of particular interest is SEMA3B, which helps guide growing nerve axons to the proper regions in the brain. Differences in the human version might help explain the different wiring in the two brains. Also the number of olfactory genes in our genome has dwindled, perhaps because we are less reliant on our sense of smell than our ancestors. Human genes involved in detecting odors-olfactory receptor genes-have accumulated more disabling mutations over time than corresponding genes in monkeys and apes.

Sequenced chromosomes from the two species have been compared and the chromosome sequences match up remarkably well. More than 98 percent of the DNA on chimp chromosome 22 is present on human chromosome 21.

The researchers found nearly 68,000 stretches of DNA that were different between the two species, including DNA that had been added to or deleted from one of the chromosomes over the course of evolution.

Human Genetics groups are also intrigued by why chimps are immune to many human diseases, such as malaria and Aids therefore by looking closely at the variation of disease genes between Chimps and humans scientists will gain a greater understanding of disease processes which in turn may lead to the development of better medicines.

References:

Nature 429:382-388 (2004)
http://www.genomenewsnetwork.org/categories/index/genome/comp/primate.php
http://www.awf.org/wildlives/6
http://www.ensembl.org/Pan_troglodytes/