Chromosomes can be studying in the cells during division, for example in bone marrow cells or cultured cells, most commonly in white blood cells that are stimulated to divide. At the appropriate color, methods appear chromosomes under the microscope as shown in the figure. The cells in the body of an individual contain, even so, set of chromosomes, and thus a full set of genes. However, some people have deviations from the normal set of chromosomes in their cells. Numerical deviations are most common, for example. Women with an auxiliary X chromosome as the sex chromosomes and chromosome number XXX in all the 47 this occurs in 1 of 800 girl births. It also women are born with only one X chromosome (45, XO, Turner syndrome, 1 in 3,000 girls), men with an extra X chromosome (47, XXY, Klinefelter syndrome, one of 400 boys), men with an extra Y chromosome (47, XYY, double-Y syndrome, 1 in 1000), and persons with Down syndrome who have autosomes No. 21 in the triple dose (47, trisomy 21, 1 in 1,000 births). Trisomy of other autosome's results in larger congenital malformations or is incompatible with life. This is reflected in a high frequency of chromosomal aberrations in cells from early spontaneous abortions.
The numerical deviation of the X chromosome had the little effect because each cell disabled their X chromosomes except one (lyonisering, first discovered by Mary Lyon in mice in 1961) therefore, the XXX-normal and fertile women.
Turner (XO) females lacking ovaries and secondary sexual development does not occur while the length of the growth is inhibited Klinefelter-(XXY) men missing who epithelial, and therefore, not developed. A slightly abnormal hormonal state often resulted evnukoid build with long limbs, wide hips and the development of breasts in light level. Furthermore, the psyche can be changed. Turner and Klinefelter syndrome shows that Y-chromosome in humans contains the male determining gene.
The XYY in males is generally increased length growth, and in some countries have found that XYY-persons cases occurring among criminals than in the general population. In trisomies are the normal gene in the triple dose instead of a double dose, and this leads to imbalance which we best knew from Down syndrome (trisomy 21). Only one autosomes, instead of two, does not provide a viable fetus. The reason for the numerical deviation of inheritance is that the two chromosomes in a pair of chromosomes do not split up as normal when the gametes are formed. This tendency increases with maternal age, in particular, under Norwegian law, women who become pregnant with 38 years of age (in our neighboring countries over 35 years of age) the provision of amniotic fluid in cell chromosome test early in pregnancy.
Structural chromosomal abnormalities are not frequent, but they are very important because the tendency to be an unbalanced chromosome ratio in the offspring can be hereditary. It is here on distinct chromosomes that have been cut, and where parts of different chromosomes have been spliced together. Such chromosomes are often called the translocation chromosome (translocation, movement). As long as both trans-location chromosome's intent found in cells of an individual, are plants that normally inherit a double dose and the individual is healthy. In some of the offspring, however, chromosome distribution will be wrong, so there is partial trisomies or monosome, and this leads to birth defects or miscarriages. Approximately, 1-2% of people with Down's syndrome have this because chromosome 21 is involved in a translocation chromosome, which is balanced by a parent. There is no age effect. For parents who were young when they had their children with Down syndrome, it is therefore, particularly important that they be offered chromosome analysis, if they think of more children. This is recommended for all parents of such children.