The number of somatic chromosomes in human body is 23 pairs, of which 22 pairs are shared by men and women and are called autosomes. The other pair is the sex-determining chromosome, which is different between men and women and is called sex chromosome. Male XY, female XX. In germ cells, the chromosome composition of male germ cells is 22 autosomes +X or Y. The chromosome composition of female germ cells is 22 autosomes+X.
The image of all chromosomes in somatic cells is called karyotype. After all the chromosomes of the cells to be tested are paired and arranged according to the Denver system, it is called karyotype analysis to determine whether they are completely consistent with the normal karyotype. Normal female karyotype: 46, xx; Male karyotype: 46, XY.
Extended data
Diseases caused by congenital abnormal chromosome number or structural distortion are called chromosome diseases. Common cases: 2 1 trisomy syndrome.
2 1 trisomy syndrome is often called congenital idiot in China, and it is the earliest and most common chromosome aberration syndrome reported.
Its main clinical manifestations: the patient's face is particularly dull, such as low nose, wide eye distance, small eye fissure, upward inclination of the outer corner of the eye, epicanthus, iris hypoplasia, strabismus and so on. All patients showed different degrees of growth retardation.
Mental retardation is the most prominent and serious manifestation of 2 1 trisomy syndrome. IQ is usually between 25 and 50. Patients with better intelligence can learn to read or do manual work; They can learn to do more work through training. Poor people have difficulties in language and self-care.
The diagnosis of 2 1 trisomy syndrome mainly depends on chromosome examination. According to the different karyotypes of patients, they can be divided into the following three types:
1 and 2 1 trisomy: About 92.5% of patients with congenital dementia belong to this type. The karyotype of the patient is 47, XX(XY), +2 1. That is, there is one more chromosome 2 1 than normal people. The main reason of this disease is that chromosome 2 1 does not separate during gamete formation. The incidence of 2 1 trisomy syndrome increases with the mother's age.
2. Chimeric type: rare, accounting for about 2.5% of patients with congenital stupidity. The reason for this type is that chromosome 2 1 does not separate during the cleavage of fertilized eggs in the early embryonic development.
The karyotype of the patient is 46, XX(XY)/47, XX(XY), +2 1. If chromosome segregation occurs earlier, the greater the proportion of abnormal cell lines, the more serious the clinical symptoms, and vice versa. Therefore, most of the clinical symptoms of these patients are not as serious and typical as 2 1 trisomy.
3. Translocation type: This type of patients accounts for about 5% of all patients with congenital stupidity. Its characteristic is that the redundant chromosome 2 1 does not exist independently, but is transferred to a chromosome in group D or G through robertsonian translocation.
Therefore, the total number of somatic chromosomes in these patients is still 46, but in fact, an extra chromosome 2 1 is attached to one chromosome, thus showing the same clinical symptoms as the typical 2 1 trisomy.
Although the total number of chromosomes is one less, the total amount of genetic material is not much different from that of normal people, and it is basically in a balanced state, so it is also called a balanced translocation carrier.
Baidu encyclopedia: human chromosomes