Chromosomal abnormalities in morphological structure or quantity are called chromosomal abnormalities, and the diseases caused by chromosomal abnormalities are called chromosomal diseases. More than 100 types of chromosomal diseases have been found, which often cause miscarriage, congenital stupidity, congenital multiple malformations, etc. In early spontaneous miscarriage, 50% to 60% are caused by chromosomal abnormalities. In couples with reproductive dysfunction such as infertility, multiple miscarriages and malformations, at least 7-10% are carriers of chromosomal abnormalities, which often do not cause disease but can lead to infertility, miscarriages and malformations due to chromosomal abnormalities in their germ cells. Second, secondary sex characteristics abnormalities Commonly found in females, such as primary amenorrhea, gonadal dysplasia, with short stature, elbow ectropion, shield chest and slightly low intelligence, few or missing pubic and axillary hairs, low posterior hairline, sterility, etc., should consider whether there is X chromosome abnormality. Early detection of these abnormalities and appropriate treatment can lead to some improvement of secondary sexual characteristics. For patients with ambiguous differentiation of external genitalia and difficulty in correctly judging the sex according to the appearance of genitalia, the examination of sex chromosomes can help to make a clear diagnosis. Children with congenital polymorphism and mental retardation and their parents Common clinical features of polymorphism and mental retardation include small head, wide eye spacing, low ear position, short neck, cleft palate, hypotonia or hypertrophy, epilepsy, through palm, anal atresia, short stature, small eye fissures, persistent neonatal jaundice and obvious cyanosis, cardiac malformation, renal malformation, iris or retinal defects, etc. Chromosomal examination may reveal abnormalities such as trisomy 21 and catarrhal syndrome. V. Sexual abnormalities Men who are tall, aggressive and have aggressive behavior may have some sex chromosome abnormalities. The incidence of the disease generally accounts for 1/750 of the male population. Most patients have a normal phenotype, i.e., good health, and are often fertile. Men who appear to have a slender stature, slender limbs, small penis, undeveloped testes and no sperm in semen, sometimes accompanied by intellectual abnormalities, should be determined by chromosomal examination to determine whether they have Creutzfeldt-Jakob syndrome, the incidence of which is 1/800 in men in general and 1 in men with mental The incidence is 1/800 in general men, 1/100 in men with mental retardation, and up to 1/10 in men with infertility. Sixth, people who have been exposed to toxic and harmful substances Exposure to radiation, chemical drugs, viruses, etc. in work and life can cause chromosome breakage, and after the breakage, the original fragment is not rejoined in its original position, which will form various structural abnormalities of chromosomes, and these aberrations can cause some corresponding diseases if they occur in somatic cells, such as Tumors. If the aberrations occur in the germ cells, the genetic effects may affect the offspring, or cause miscarriage, stillbirth, or deformed children. Seven, the newly married population premarital examination can be found phenotypically normal abnormal chromosome carriers, these patients are very likely to cause miscarriage, abnormal fetus, stillbirth, blind birth control will cause an increase in the birth rate of malformed children; can also be found phenotypically normal, but chromosomal abnormalities, these patients can be manifested as reproductive disorders, fertility, etc.. Therefore, premarital examination is of great significance to eugenics.