Primary translocations, formed by reciprocal and complex translocations, are called balanced translocations because there is basically no loss of genetic material and they generally have no serious effect on the development of the individual. Carriers of balanced translocations are also at high risk of miscarriage. Carriers of balanced translocations have normal phenotype and intelligence because they have no loss of their own genetic material, but their germ cells produce 18 gametes in meiosis, of which only 1/18 are normal, 1/18 are balanced translocation carriers, and the rest are unbalanced gametes, which can lead to recurrent miscarriage or malformed fetuses, or Adverse birth history. The principle of occurrence is that two chromosomes of different origins are disrupted and rejoined to form two structurally rearranged chromosomes called reciprocal translocations. Most of these translocations retain the original total number of genes and generally have no serious effect on gene action or individual development, so they are called balanced translocations. In meiosis, if two translocated chromosomes are together and two normal chromosomes are together in a germ cell, balanced gametes will be produced because such a separation ensures that each cell has a complete set of genes. If a translocated chromosome and a normal chromosome separate together and enter the germ cell, an unbalanced gamete will be produced. Balanced translocations are the most common type of chromosomal structural aberration in humans, with an incidence of about 1/500 to 1/1000 in newborn infants. In layman’s terms, humans have 23 pairs of 46 chromosomes, and the number and structure of chromosomes are relatively constant; you can’t just have a little more or a little less, or something could go wrong. A balanced chromosomal translocation is when two chromosomes break and are exchanged with each other, with only a change in position and no visible increase or decrease in chromosomal segments. This translocation results in an “internal move” of the chromosomal genetic material. However, in a cell, the total number of chromosomes remains the same and the genes contained are not added or subtracted, so carriers of balanced translocations usually do not have an abnormal phenotype and usually have normal appearance, intelligence and development. However, it is possible for a child born from a marriage between a carrier of a balanced translocation and a normal person to receive a derived abnormal chromosome, resulting in an increase (partial trisomy) or decrease (partial monosomy) in a particular translocation segment, with corresponding effects. Since the fetus receives one chromosome from each parent to form its own chromosome, if he does not inherit all of his father’s (mother’s) translocated chromosomes, or if he does not inherit all of his father’s (mother’s) normal chromosomes, but only one translocated derived chromosome, this results in a situation where the total amount of genetic material is incorrect, resulting in the absence (partial monosomy) or excess (partial trisomy), which disrupts the balance of genetic material and leads to fetal malformation or spontaneous abortion.