Human Evolution: Big gains and small but Important Losses
Found "gaps" in the genome that deprived people of "cat whiskers"
RIA NewsA comparison of the genomes of chimpanzees and humans has revealed a number of human genetic features that deprived him of some anatomical features that are widespread among mammals, for example, sensitive "whiskers"-vibrissae and keratin spikes on the penis, and also led to an increase in brain size, the journal Nature reports (How the penis lost its spikes).
A group of scientists led by David Kingsley from Stanford University in the USA is searching for genetic features that appear externally in the form of anatomical, physiological and behavioral differences between humans and animals.
In search of such differences, scientists compared the human genome with the genome of our closest relative, the chimpanzee, with whom humans genetically match 96%. As it turned out, humans are distinguished from monkeys and other mammals mainly not by genetic acquisitions, but by losses – the absence of some DNA fragments, the so-called deletions.
"We have identified molecular changes that are highly likely to lead to significant changes in the human regulatory apparatus. This is a complete deletion of genetic sequences that are well preserved in chimpanzees and other mammals. We have confirmed 510 such deletions in humans," says an article published by Nature (Human-specific loss of regulatory DNA and the evolution of human-specific traits).
Such unexpectedly "empty spaces" that are "filled" in almost all other animals, in particular, fell on one of the fragments of the genome associated with the production of the AR receptor protein (androgen receptor), which reacts to male hormones - testosterone and dihydrotestosterone.
This protein is responsible for the reaction of body tissues to sex hormones and with a high degree of probability can be associated with secondary sexual characteristics. Scientists have suggested that the loss of this genetic fragment led to the disappearance in humans of two traits characteristic of both chimpanzees and many other mammals – hard sensitive hairs-vibrissae, as well as keratin spikes on the penis. Such spikes, tough skin growths about a millimeter high, are present in many mammals, from mice and cats to monkeys.
"Sensitive vibrissae develop in many mammals, including chimpanzees, macaques and mice, but humans lack them. The development of vibrissae is associated with male hormones, since castration shortens the vibrissae in mice, and excess testosterone stimulates their growth," the article says.
Scientists conducted experiments observing the development of embryos of chimpanzees and monkeys deprived of the genetic fragment in question and confirmed its connection with both anatomical features.
The authors of the work note that the absence of thorns on the penis can cause many features of not only sexual, but also social behavior of a person, in particular, the appearance of monogamy and the care of offspring on the part of fathers.
Another "missing" fragment in the human genome is located next to the GADD45g gene. The latter controls the growth of cells, and its absence leads to their uncontrolled growth and the appearance of cancerous tumors. However, deletion next to this gene was associated with an increase in the size of a number of brain regions in humans.
An experiment on embryos of mice and chimpanzees deprived of this site showed that their visual areas of the brain and a number of other areas begin to increase.
However, the authors of the study note that this gene alone does not determine all the features of the human brain.
Portal "Eternal youth" http://vechnayamolodost.ru10.03.2011