Chromosomes are the transmitters of genetic information. They ensure that physical characteristics of the parents are passed on to their common children. At the same time, serious diseases can occur when chromosomes are disrupted.
What are chromosomes?
DNA are the basis for heredity. This is present rolled up in the form of chromosomes. Humans have 46 chromosomes. Of these, 23 come from the mother and 23 from the father. Except for germ cells, every cell in the human body has 46 chromosomes. The number of chromosomes differs from species to species, but does not provide information about the development of the organism. Blackbirds, for example, have 80 chromosomes. The chromosomes occur in homologous pairs. This means that in each case two chromosomes are responsible for reproducing a genetic information. Of the 46 chromosomes, two are called gonosomes. Their task is to determine the sex. The chromosomes are located in the cell nuclei, which are also called carriers of the genetic material. If their structure were unrolled, it would measure a length of about 2 meters. During cell division, the chromosomes also divide. This process is called mitosis or meiosis. Meiosis takes place in the germ cells, egg cell and sperm, mitosis in all other body cells. In this process, the chromosomes present are reproduced so that they are always identical.
Anatomy and structure
Chromosomes are made up of two halves. These are often not the same length and are called chromatids. In the middle, the halves intertwine. Chromosomes that join at one of the ends of the chromoatids are called submetacentric. In this case, the arms appear shortened. The site where the halves unite is called the centromere. During mitosis and meisoe respectively, the chromatids divide at the centromere and are pulled to the cell ends. Since each cell carries genetic information, it is necessary that this is also duplicated during cell division. In this process, the chromatids consist of DNA that is rolled up. This in turn staggers into a double strand. In the double strand, two base pairs are combined with each other. These are opposite each other and run in a complementary manner. Of the four different base pairs, only two ever fit together. The arms of the chromosome are usually in a position that looks like an X.
Function and tasks
Chromosomes have two special tasks: First, they determine the sex of the child, and second, they provide it with all the genetic information that is necessary. These include, for example, the color of eyes and hair. The inherited information comes from the mother and father. That is why chromosomes always occur in pairs. The characteristics are inherited dominantly or recessively. Since from mother and father in each case the same characteristic is passed on and thus for example the information for two different eye colors would be present, one of the characteristics must prevail in the further process. In addition to external characteristics, chromosomes are also responsible for the development of abilities and behavior. Furthermore, they can transmit existing diseases to the newborn. In contrast, acquired characteristics, such as a large muscle mass, are not inherited. In the case of sex, only the 23rd chromosome plays a role, the so-called gonosome. The sex chromosomes are divided into X and Y chromosomes. Females have two X chromosomes, males have one X and Y chromosome. Accordingly, it is ultimately the sperm that decides which sex is inherited, because females only have X chromosomes and thus cannot inherit a Y chromosome.
Complaints and diseases
Without the chromosomes, inheritance could not occur either. Accordingly, major complications can arise if the number or shape is not correct. Down syndrome, also known as trisomy 21 among experts, is particularly well known. The name already gives information about the problem at hand: instead of existing twice, the 21st chromosome exists 3 times. Affected children show developmental disorders, but also physical complaints, such as heart defects. In Turner syndrome, on the other hand, one chromosome is missing. The disease can only affect girls because the missing chromosome is the second X chromosome.Patients report short stature as well as infertility. A striking feature of chromosome disorders is that in women who have two X chromosomes, damage to one of the gonosomes can be compensated. On the other hand, this is not the case in men. The fact can be explained by the fact that men have only one X chromosome, which means that defects on this one cannot be compensated. This results in hereditary diseases that affect almost only men. Examples are red-green disease, hemophilia or Duchenne’s muscular dystrophy. In only very few cases are the patients women. In general, defects in chromosomes can occur during cell division, the fusion of egg and sperm cells, or during the formation of germ cells. Such a process results in the presence of too many or too few chromosomes. It is also possible that the structure of chromatids is damaged. In addition, it cannot be ruled out that certain external influences have a negative effect on the chromosomes. These include, for example, radiation or some chemicals. Diseases based on a defect of the chromosomes cannot be treated. It is only possible to mitigate the consequences that arise.
