Every human body cell, except for sperm and egg cells, contain 46 chromosomes. These contain around 100000 genes that between them determine all of an individual’s characteristics, from hair colour to potential height. Sperm and egg cells each contain 23 chromosomes. When they fuse during fertilization, the chromosome number is restored to 46, or 23 pairs of chromosomes. Thus everybody cell nucleus contains 23 paternal chromosomes paired up with 23 maternal chromosomes.
DNA fingerprinting, also known as genetic finger printing this process is used to reveal the genetic identity of an individual. The arrangement of bases within his or her DNA is unique to that individual, just as his or her fingerprints are; the only exceptions are identical twins, who share the same DNA. A tissue sample, usually of blood, is taken from the person and DNA molecules are then cut into small pieces and separated. By adding a radioactive probe, and using an X-ray film, a banded strip is produced, unique to its owner. The more closely two people are related, the greater the similarity between the pattern of bands. Genetic fingerprinting was used to confirm the human remains found in Russia were those of the Romanovs, the Russian royal family, by comparing DNA fingerprints from the remains with those of the Romanovs’ living relatives. Genetic fingerprinting is similarly used to prove paternity. In criminal cases such as rape, DNA extracted from the perpetrator’s semen or other body fluids can be used to confirm his identity.