The X-chromosome is found in both females and males. Females have a pair of two XX chromosomes and males have an XY chromosome pair. Both the X and Y chromosome contain relatively little genetic material when seen in view of other chromosomes. They contain repeated parts of DNA; the X-chromosome carrying about 2000 out of the 25000 or so genes, and the Y-chromosome about 78. Females inherit an X-chromosome from the mother and an X-chromosome from the father. Thus, testing this chromosome is crucial when it come to determining relationships between females in DNA relationship testing and the genetic test involves mapping genetic profiles in X-Chromosome Testing.
We are all born with 23 pairs of chromosomes, one pair of which are our sex chromosomes. Both males and females have at least one X chromosome in every pair, which is given to them by the mother. Despite the fact we say that we all have a total of 46 chromosomes, there are some chromosomal abnormalities which can lead to people having extra X chromosomes, deletions of the chromosome or point mutations. Such conditions include Klinefelter syndrome, XYY syndrome, Trisomy X)
Female eggs cells are homogametic meaning that females generate only eggs containing X chromosomes. In order to produce a zygote, it is necessary that two gametes fuse together, one from the male and one from the female. Since the female only produces X chromosomes and males produce both X and Y-chromosomes, it is the male gamete (sperm) that ‘decides’ on the sex of the baby. In birds, frogs and some types of insects and fish this is the inverse: female gametes are responsible for sex determination. In birds in fact, we have a ZW chromosome sex determination. Females have ZW chromosome pairs and males have ZZ chromosome pairs. It is clear that in the world of brids, it is the female and not the male that determines the sex of the offspring. Interesintingly, as humans we share a lot of DNA with other animals and even some insects, such as the fuit fly, with which we share around 60% of our genes.