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The study of inheritance occurred in human beings is called genetics. Human genetics overlaps a lot of fields, like cytogenetics, genomics, developmental genetics, counseling and molecular genetics. All the studies made in these fields try offering answers for questions about human nature, about humans' diseases, and they help understanding genetics of human life.

The inheritance patterns for humans are based upon Gregor Mendel's model; he deduced that this inheritance process depends upon units of inheritance, called genes. Gregor Mendel was a priest, but a scientist in the same time, and he is the father of genetics. He studied pea plants and he slowly created this model for inheritance characters. His work significance has not been recognized until the beginning of the 20th century, when the scientific society rediscovered his work and this meant that the base of the modern science of genetics was formed.

Gregor Mendel lived in a monastery in Brno and there he cultivated and tested more than 29,000 pea plants between 1856 and 1863. He deduced two general aspects, which later became known as Mendel's Laws of Heredity or Mendelian inheritance. He published in 1866 these laws, in a publication of the Natural History Society of Brno.

The first law of segregation says that mixing one trait will result in the first generation in a 3:1 ratio and this means that 3 of the "children" in the first generation will have the dominant gene, and one will not. The second law reffers to mixing two inherited traits (dybhibrid cross), and it says that the children generation will have the traits in a 9:3:3:1 ratio. These laws are illustrated in the following images.

There are some inheritance processes which do not respect the Mendelian laws and the traits don't segregate in accordance with these patterns. These non-Mendelian segregation can be observed at viruses, fungi and bacteria, and usually all exceptions which happen in the eukaryote reproduction are categorized like this.

There are some simple human traits which follow these laws, and here are some examples of dominant traits which segregate upon these simple laws: ability of tasting Phenylthiocarbamide (also known as PTC; it is a bitter chemical compound), the unattached earlobe, the normal thumb (in this case, the recessive trait is Hitchhiker's Thumb , the dark color of human iris, facial dimples are also Mendelian traits as well as normal pinkies (the recessive gene brings crooked pinkies.



In human inheritance, errors may occur, and in these situations genetic diseases appear. They are caused by recessive genes, and here are some examples: Turner Syndrome, cancer, autism, Cri-du-Chat syndrome and Klinefelter syndrome. Cri-du-chat is caused by the shorter arm of the 5th chromosome, and this results in mental retardation, problems in behavior and a cat like sound. This syndrome occurs at one case in 50,000 births. Klinefelter affects only men and it is caused by the presence of an extra X chromosome. The genotype of these individuals has on the 47th position a XXY type and not the normal XY type. The symptoms are small testes, sterility and enlarged breasts.



Nowadays, with all technology available, studying genetics is much easier than in Mendel's time, and all observations are made at a much smaller level than he did. Now there are powerful microscopes, which can offer a great view on the combination and linkage processes.There are research programs which aim to solve nowadays society's problems with diseases and the most important research programmes are in cancer and AIDS treatment developments programmes. An important event was the decodation of the human genetic code, and Craig Venter was the first person who published his genetic code online (2007). The costs for this decoding process are big, around $250,000 and until now, 12 codes have been decoded almost integrally. It is supposed that until 2013 the price for genetic code mapping to be around $1,000 and the time required for this mapping to be around 15 minutes.



There are four nitrogenous bases of the DNA alphabet: A, C, G, T which stand for Adenine, Cytosine, Guanine and Thymine. These bases pair and they carry the instructions for creating all the organisms. When they group in blocks of three letters, an amino acid results and there are 20 different vital aminoacids which produce proteins. The fruit fly has 13,000 genes, the nematode worm has 18,000 and humans have between 30,000 and 40,000 working genes in their genetic code. Humans are different of other organisms by the fact that our genes have different roles and because we have more control genes than animals. Most of the mutations occur in male human organisms and as an interesting fact, in 0.0004 inches of DNA, there are encoded six feet of information. In the 100 trillion cells of the human body there are 3 billion letters part of the DNA code. Scientists suppose that not all the genes in the genetic code have a specific protein-creating role, and that there are also support genes, and they make analogies with the brain tissue, which is made of neurons, the basic cells, and the glial cells, which only offer support for the neurons.

The big fights are given now on stem cells and cloning battlefields, and scientists are trying to solve these main issues, because they are the keys for progress in medicine and in preventing and treating a lot of diseases which affect nowadays a lot of people. Both stem cells and cloning have been subject of a lot of ethical controversies and the opinions differ from person to person. Using stem cells would be a great achievement because a lot of affected organs could be "replaced" and cloning sound like futuristic scenarios but it would also be a cool achievement for science.