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X linked Recessive Inheritance Generally, it manifests only in males. A male with an affected allele on his single X chromosome is hemizygous and can not transmit the disorder to their male offsprings, but all his daughters would be obligate carriers. Healthy heterozygous carrier females pass the disorder to affected sons. So from affected males, it can be transmitted to male grandchildren through carrier daughter ('diagonal' or 'Knight's move' transmission). RISK CALCULATION: The X chromosome from a male is transmitted to daughters, and the Y chromosome is transferred to sons. If an affected male has kids with a healthy female, none of his male offsprings will be affected, but all of his female offspring will be carriers. If a carrier female has kids with a healthy male, each male offspring has a 50% chance of being affected, and female offspring have a 50% chance of being a carrier. VARIABLE EXPRESSION: Heterozygous female are those who are having mutant allele on one X chromosome, and normal allele on another X. Heterozygous female may have a variable expression of X linked recessive disorder due to the random process of X inactivation involving inactivation of the X chromosome with a mutant allele in some cells while inactivation of the X chromosome with a normal allele in other cells (mosaic pattern). X-LINKED DISORDERS IN FEMALES: Sometimes, females might be affected by X linked recessive disorders. This fact is explainable by one of the following possibilities. (a) Heterozygosity: X inactivation is a random phenomenon that can involve a mutant allele containing X and a normal allele X in equal proportion in the heterozygous female. It is a possibility that the active X chromosome in the majority of the cells of a heterozygous female is the one having a mutant allele (skewed X inactivation), leading to disorder expression; this has been the case in Duchenne muscular dystrophy and hemophilia A. (b) Homozygosity: When both X chromosomes of females have a mutant allele, as reported in hemophilia A and ichthyosis. (c) Translocations: If a female is having a translocation involving an autosome and one of the X chromosomes and the translocation disrupts a gene on an X chromosome, in that case, a female might be affected. This pattern has been observed in Duchenne muscular dystrophy.[10][11][10] (d) A female having only a single X chromosome (Turner syndrome), which is bearing a mutant allele. Hemophilia has been reported in the girl infant with the turner syndrome.[12] X linked Dominant Inheritance Male and female both are affected, but females are affected in excess and less severely. Affected males can transmit the mutant allele to female offspring but not to male offspring. Affected females can transmit the mutant allele to 50% of his male offspring and 50% of his female offspring. examples are Vitamin D resistant (hypophosphatemic) rickets, Charcot-Marie-tooth disease. Some X-like dominant disorders, such as incontinentia pigmenti (Bloch-Sulzberger syndrome), showed a mosaic pattern of involvement for heterozygous females. X-LINKED DOMINANT LETHALS: These disorders are incompatible with early embryonic survival. They are seen only in females and not in males because, in the severe form, they will cause the death of a male embryo, but as females are less severely affected female embryo will survive. Keywords: If a disease with dominant X-linked inheritance affects 1/100 of males in a population, what is the frequency of that gene in the population? What portion of females in the population will be affected by the dominant X-linked disease? #XlinkedGeneticDisorder #XChromosome #XchromosomeLinked #geneticDisease #probability #statistics #Genetics #biology #XlinkedTraits #genotype #phenotype #KhanAcademy #NikolaysGeneticsLessons #geneticDisorder #DNA #RNA #geneticsDisorders #homozygous #hemizygous #chromosomes #XChromosomeInheritance #dominantTrait #geneticDesease #XlinkedRecessive #AutosomalRecessive #GeneticsExamQuestionsSolutions #SexlinkedDominant #skewedXinactivation #Xlinked
