Organism with a recessive genetic allele that does not display the recessive trait
Punnett square: If the other parent does not have the recessive genetic disposition, it does not appear in the phenotype of the children, but on the average 50% of them become carriers.
A hereditary carrier (genetic carrier or just carrier), is a person or other organism that has
disease. Carriers are, however, able to pass the allele
onto their offspring, who may then express the genetic trait.
Carriers in autosomal inheritances
Punnett square: If both parents are carriers, on the average 25 % of the offspring have the recessive trait in phenotype and 50 % are carriers.
diploid
). Carriers can be female or male as the autosomes are homologous independently from the sex.
In carriers the expression of a certain characteristic is recessive. The individual has both a genetic predisposition for the
hereditary disease
.
Carriers in gonosomal inheritances
The mother is a carrier of the recessive hereditary disposition for Color blindness. The Y chromosome of the father cannot oppose this. The healthy allele on the X chromosome of the father can compensate for this in a daughter. She can see normally, but she becomes a conductor. The same pattern of inheritance applies to Haemophilia.
cannot be carriers because they only have one X chromosome. The Y chromosome is not a really homologous chromosome. For this reason, the genetic make-up of the observed trait is not twofold. If a man has a certain recessive genetic disposition on his X chromosome, this is called hemizygous and it gets phenotypically expressed. Also a recessive genetic disposition on his Y chromosome - also hemizygous - can come to expression, because there is no homologous chromosome with an allele, which could overlay it. If there is no genetic information on the Y chromosome for a certain trait, the effect of the Y is neutral and the allele on his X chromosome, which would be recessive in a heterozygous woman, can now alone come to expression.
Women have two homologous sex chromosomes (XX). Therefore, women can be carriers of X-linked genes. Examples of traits inherited via the X chromosome are color blindness and the most common hereditary form of Haemophilia. Men are affected much more often than women.[1][2]
Inheritance by female carriers
X-linked recessive gene would cause them to be an asymptomatic carrier. These females simply passed it to half of their children.[4]
Gonosomal dominant inheritances are also known. There are no carriers since owners of a dominant hereditary disposition phenotypically express the trait in each case.
