DNA, chromosomes and genes
Genetics is the study of biological inheritance. Arvelighed means that different characteristics or properties transferred from parents to children. Children are similar to their parents, because they have a combination of parents' genetic heritage. Arvemassen consists of DNA. A DNA molecule is a chain of so-called nucleic acids, arranged in a particular order. There are two strands in each DNA molecule, and these severe winds its way as two spirals on each other.
DNA is folded and arranged in slightly larger structures called chromosomes, and in almost all cells throughout the body, there are 23 kromosompar, that is 46 chromosomes in total (an exception is the sperm and egg cells, where only 23 chromosomes). In each kromosompar comes one chromosome from the mother and the other from the father. It is the same 46 chromosomes, which are reflected in all the cells. Two of kromosomerne is known kønskromosomer and called X or Y. It is the combination of these kønskromosom
Genes are certain pieces of a DNA molecule, and each gene is a kind of code for a particular protein. What genes that become active and thus transmit its specific information to the child is determined by how kromosomerne from the mother and father shared, and how the genes in each part of a kromosompar connected.
Generne can have two different characters: recessive or dominante. A dominant gene is expressed in the child regardless of the nature of the modsidige gene in kromosomparret. A reccesivt gene comes only expressed by the child, if it modsidige similar to. A classic example is the gene for brown and blue eyes.
Genet for brown eyes is dominant, while the gene for blue eyes is recessive. So if one of the parents transfer the gene for brown eyes and the other the gene for blue, your child, brown eyes. You could say that the gene for brown eyes is stronger than the gene for blue eyes. In order to have blue eyes, the two genes for eye color be the gene for blue eyes. A person with brown eyes, in many cases have both a gene for blue and a gene for brown eyes. If two such persons have a child together may well get the baby blue øjn
Monogene hereditary diseases
Monogene hereditary diseases occur because a faulty gene transferred to the child from either one or both parents. We are also talking here about dominant and recessive. A dominant hereditary disease will be transferred to the child if just one of the parents transfer a sick gene, as dominante diseases require only a sick gene. Examples of dominant hereditary diseases are Huntingtons chorea (santvejtsdans) and osteogenesis imperfecta (a kind of inborn osteoporosis ). These diseases are relatively rare in Denmark.
A reccessivt hereditary disease, can only be transferred to the child if both parents transfer a sick gene. If only a sick reccessivt gene transfer, the child becomes a carrier of the disease. One example is cystic fibrosis Where 1 out of 20 Danes are carriers of the disease gene. In order to have the disease, we must inherit the disease gene from both parents, so even if the gene for the disease are relatively frequent in the population will have only one child out of some. 4200 disease.
A special group of the monogene hereditary diseases are the X-bound (kønsbundne) hereditary diseases. These diseases are, in principle, recessive, but is localized to one of the genes on the X chromosome. Because boys have only one X-chromosome, they are much more likely to have X-bound hereditary diseases, since they have no quick version of the same gene. A girl who inherits a defective gene on one X-chromosome, will still have a healed gene on the second X-chromosome and is therefore only a carrier of the disease. Eksemple Blødersygdommen and Duchennes muskeldystrofi . Both seen almost exclusively in boys.
Polygene hereditary diseases
Polygene hereditary diseases caused by defects in different genes. Arveligheden is very complex, and in many cases we do not know the exact genes that cause disease. Often, it is not a specific disease, which inherited, but rather tend to become ill. This applies for example general cardiovascular diseases , Which in some families is an increased incidence of these diseases. Here it is not only inheritance, which plays a role but other factors such as smoking , overweight and too little motion . For many of the polygene hereditary diseases there is the opportunity to influence the risk of developing disease.
If you have inherited diseases in the family and plan to have children, you can get help to assess the risk that one's children will be ill. This is done by so-called genetic counselling .