The so-called recessive inheritance means that parents carry a certain gene but do not become ill, and their genes will become ill after being passed on to their offspring.Autosomal recessive polycystic kidneyThat's the case. His previous generation carried this gene, but he didn't have it all his lifePolycystic kidneyThe offspring will become ill after obtaining this gene through heredity, andInfancy(Some even in the fetal period) shows very serious symptoms.asRed green colour blindness、hemophilia、Albinism。
Dominant hereditary disease(AA or Aa) means whether or not to suffer fromDominant geneA decision, that is, as long as there is an A, it is dominant, and it will be ill. AA and Aa are both ill, but aa is notPathogenic gene, will not get sick
classification
Announce
edit
Recessive inheritance can be divided intoSex linked inheritanceAnd non sex linked inheritance.
Non sex linked recessive inheritance
UnaccompaniedRecessive hereditary disease(Aa or aa) means that the disease is determined by a and has nothing to do with chromosome X/Y. As long as A is present, it will be dominant, while the disease is recessive, so it will be ill only when aa is present.
give an example:
For example, the morphological basiscapital, such as A
Two genes together form a pairAlleleThere are three kinds of AA, Aa and aa
As long as there is one A, such as AA, Aa is dominant
X-linked recessive inheritance
A trait orHereditary diseaseThe relevant genes are located on the X chromosome. The nature of these genes is recessive, and they are passed along with the behavior of the X chromosomeGenetic modebe calledX-linked recessive inheritance（X-linked recessive inheritance,XR）。
When inherited recessively, women have twoX chromosomeWhen the recessive pathogenic gene is in the heterozygous state (XAXa), the trait or genetic disease controlled by the recessive gene does not show up, so the female phenotype of the pathogenic gene is normalcarrier。Only when the alleles on both X chromosomes are recessive pathogenic genesHomozygote(XaXa).In male cells, there is only one X chromosome,Y chromosomeThere is no homologous segment on the X chromosome, so as long as there is a recessive pathogenic gene (XaY) on the X chromosome, the disease will occur.In this way, there is only one gene in a pair of alleles in male cells, so it is calledHemizygote（hemizygote）。
Red green colour blindness
Red green colour blindnessIt is a recessive disease on the X chromosome (with X recessive inheritance).Color blindnessAccording to the color of color vision disorder, it can be divided into red blindness, green blindness, purple blindness, panchromatic blindness, etc.[1]The former can not distinguish any color and is generally considered to be autosomal recessive inheritance;The latter is the most common, which is manifested by the decreased discrimination of red and green.X-linked recessive inheritance, causing diseaseGene mappingOn Xq28.Reportedly, menincidence rate7.0%, 0.5% for women. A red green blind male patient (XbY) married a woman with normal color discrimination ability (XBXB). Their daughters should receive an X chromosome from their father, and get a normal X chromosome from their mother to become a disease gene carrier hybridized (XBXb). Their sons must receive an XB from their mother, so their color discrimination ability is all normal (XBY).In the next generation, half of the sons are normal (XBY), half are green blind (XbY), half of the daughters are disease gene carriers (XBXb), and half are completely normal (XBXB).Therefore, the father of a female patient must be the patient, and the mother must be the disease gene carrier.Here we can see the "father to daughter, mother to son"Cross inheritance(crisis cross inheritance). If a female carrier (XbXb) marries a male patient (XbY), 1/2 of the offspring may be infected (XbXb), 1/2 may be carriers (XBXb), and 1/2 of the offspring may be infected (XbY) and normal (XBY).
The red green blind pedigree can reflect the X-linked recessive genetic pedigree and characteristics, which are manifested in: ① male patients are far more than female patients; ②Both parents of male patients are disease-free, and the pathogenic gene comes from the carrier mother; ③Due to cross inheritance, the siblings, unclesmaternal cousinsbrother、nephewIt is common to see the patient, and the maternal grandfather is occasionally ill. In this case, the uncle of the male patient is generally normal; ④Since the children of male patients are normal, it is obvious from generation to generationDiscontinuity（Atavism）。
