Chromosomes consist of wound DNA (deoxyribonucleinacid) and are located in the nucleus of every human cell. Although the number of chromosomes in each species varies, the amount of chromosomes of one species per body cell is identical. Humans have 23 pairs of chromosomes (diploid) and 46 individual chromosomes (haploid). However, the comparison with other living organisms shows that the number of chromosomes does not provide information about the developmental status of the species. While the blackbird has 80 haploid chromosomes, the mosquito has only 6 haploid chromosomes. The chromosomes are compressed in the cell nuclei so that they would come in spread out form to a length of 2 meters.
In humans and a variety of animals, sex is determined by the chromosomes. Here one distinguishes the gonosomes (sex chromosomes) from the autosomes. In humans, the chromosome pairs 1-22 are autosomal and thus gender-independent and the 23rd chromosome pair is responsible for sex determination.
In humans, there are two different sex chromosomes, the X and the Y chromosome. Women have two X chromosomes in twenty-third place, while men have one X and one Y chromosome, which can lead to hereditary diseases.
If there is a gene defect on this single X chromosome, it can not be caught by the other chromosome. Women have two X chromosomes at this point, so a healthy chromosome 23 can compensate for the other's defect. The best known examples of hereditary diseases, which therefore occur almost exclusively in men, are red-green blindness, Duchenne muscular dystrophy, and hemophilia.