Conductor

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Inheritance scheme : If the other parent does not have the recessive genetic makeup in question, it does not appear in the children, but 50% of them become carriers.
Here are both parents conductors. 25% of the offspring have the trait in the phenotype and 50% become carriers.

A conductor ( transmitter or carrier ) for a certain trait is an individual who has the genetic make-up for a trait without having this trait himself. The English term carrier is also often used. As a conductor is any organism with a recessive allele that with him as heterozygous carriers of the genetic trait phenotypically not its appearance, but by him to the following generation inherited can be.

Conductors in autosomal inheritance

There are conductors u. a. in autosomal dominant-recessive inheritance patterns, i.e. inheritance patterns in which the expression of a certain characteristic takes a back seat to another, i.e. is recessive (from the Latin recedere to withdraw ). The characteristic that is expressed instead is called dominant . If an individual has both a hereditary disposition for the dominant expression and a genetic predisposition for the recessive expression of a characteristic, the dominant expression prevails. The appearance ( phenotype ) of the individual then corresponds to the dominant genetic makeup. A dominant-recessive inheritance is possible because the individuals of most species (including all higher animals and plants) from most of the genetic makeup each have two alleles for a characteristic , because the chromosomes in the cell nuclei are usually in pairs ( diploid ).

In the case of an individual who is heterozygous , i.e. who has the genetic makeup for the dominant and the recessive expression, it is not externally recognizable that he / she also has the recessive genetic makeup. Such an individual is called a conductor . However, if this individual has offspring, the recessive expression can emerge. This happens when the offspring receives the recessive allele from both parents, i.e. does not have a dominant allele that would cover up the recessive genetic makeup. Conductors can inherit healthy recessive hereditary traits or autosomal recessive hereditary diseases . A recessive hereditary disposition can phenotypically only appear if two conductors produce offspring together . Then, according to Mendel's rule of division, an average of 25% become homozygous and thus bearers of traits or those affected.

Conductors in gonosomal inheritance

Inheritance schema : The mother (left) carries the recessive hereditary disposition for red-green poor eyesight . The father's Y chromosome (above) cannot do anything to counter this. The healthy allele on the father's X chromosome, on the other hand, can provide a balance in a daughter. She has normal color vision, but is a conductor. The same inheritance pattern applies to hemophilia .

In gonosomal inheritance, too , conductors only pass on recessive genes . The term "conductor" is used particularly often in human genetics when it comes to inheritance in which the trait is on the female sex chromosome , on the X chromosome ( X-linked inheritance ). The conductors here are always women ( gonosomes XX ) and are therefore referred to as conductors. Men ( gonosomes XY ) cannot be a carrier in such inheritance because they only have one X chromosome and therefore their two sex chromosomes do not have a really homologous chromosome. Therefore, the genetic disposition for the trait is not present twice. If a man has a recessive genetic make-up on his X chromosome, it is called hemizygous and this genetic make-up is phenotypically expressed in him. An inherently recessive genetic make-up on his Y chromosome - also hemizygous - can develop , as there is no homologous chromosome with a corresponding allele that could overlap it. However, if there is no genetic information at all about a genetic characteristic on the Y chromosome, the effect of the Y chromosome is neutral and an inherently recessive genetic makeup on its X chromosome can now be fully developed.

In contrast, women have two homologous sex chromosomes (XX). You can heterozygous have the recessive and the dominant genetic makeup and thus be a carrier. Examples of a characteristic that is inherited in this way on the X chromosome are the red-green color blindness and the most common inherited form of hemophilia ( hemophilia ). Men are affected much more often than women.

Orange tomcat when marking
Heterozygous she-cat with puppies

An example from the animal world of X-linked recessive inheritance is the allele for orange fur in domestic cats . There is a recessive allele for orange fur on the X chromosome, which is why orange specimens are mostly tomcats. The males are hemizygous and therefore genetically hereditary in terms of the genetic makeup for orange. In female cats, only those with a homozygous genotype develop the orange coat color in the phenotype (see X-linked inheritance ).

In addition, very rare gonosomal dominant inheritance patterns are known. However, there are no conductors for such , since humans and animals with a dominant genetic disposition develop the characteristic phenotypically in any case.

See also

Individual evidence

  1. ^ Neil A. Campbell , Jane B. Reece : Biology. Spektrum-Verlag 2003, ISBN 3-8274-1352-4 , pages 308-311.
  2. ^ Ulrich Weber: Biologie Gesamtband Oberstufe, Cornelsen-Verlag 2001, ISBN 3-464-04279-0 , pages 178-182.