The obvious recessive formula of sex in biological inheritance is: out of nothing, it is recessive, recessive inheritance depends on female disease, and the sentence that female sick father and son are normally "often hidden" summarizes the law of sex chain inheritance.

Sex-linked inheritance means that some traits of offspring are controlled by genes on sex chromosomes in the genetic process. This inheritance mode of traits controlled by genes on sex chromosomes is called sex-linked inheritance, also known as sex-linked (inheritance) or sex-linked connection. Many organisms have sex-linked genetic phenomena. Among humans, the most clearly understood is the sex-linked inheritance of red-green blindness and hemophilia.

If the parents are normal and the children have patients, it must be a recessive genetic disease. (there is something hidden out of nothing)

If both parents are sick and the child is normal, it must be a dominant genetic disease. (out of nothing is dominant)

Recessive inheritance shows that sick father and son are "often hidden" under normal circumstances. That is to say, if it is a recessive genetic disease, find a female patient in the genetic pedigree to see if her father or son is a patient. If one of her father or son is not a patient (normal), then this family is definitely not a sex-linked (with X chromosome or Y chromosome) genetic disease, but an autosomal recessive genetic disease.

Sex-linked inheritance can be summarized as follows:

1, when homozygous chromosomes (such as XX for mammals and ZZ for birds) transmit homozygous dominant genes, both sexes of F 1 are dominant traits. The segregation of F2 traits is 3 dominant: 1 recessive; The gender separation is 1 female: 1 male. The sex of recessive individuals is the same as that of their ancestors, that is, 1/2 grandchildren have the same phenotypic characteristics as their ancestors.

2. When homozygous chromosomes transmit homozygous recessive genes, F 1 shows cross inheritance, that is, the mother's traits are passed on to her son and the father's traits are passed on to her daughter. In F2, the ratio of traits to sex is 1: 1.

3. Traits determined by genes existing in the differential segment of Y chromosome (especially mammals) or by genes carried by W chromosome are only passed from father (or mother bird) to son (or mother bird). It shows a special Y-linked (or W-linked) inheritance.

4. There are more female patients with X dominant genetic disease than male patients; There are more male patients with X recessive genetic disease than female patients.