XLinked Recessive Write three rules to keep in mind when cou

X-Linked Recessive Write three rules to keep in mind when counseling someone about the likelihood of inheriting an X-linked recessive condition: About parents\' genotype. About parents\' phenotype. About the probability of the offspring showing the trait. If instead of having Hemophilia C (autosomal recessive), Lisa Keller\'s brother had Hemophilia A (X-linked recessive), what would be the probability that she was a carrier? 25% 50% 67% 100% More information is required to answer this question.

Solution

About genotype of parents- If the mother is a carrier i.e. carrying the recessive allele on one of her X chromosome and the father do not have the recessive allele in his genotype, then none of the daughters will suffer from the disease (since they will inherit only one recessive allele from the mother) but sons will have a 50% probability of suffering from the disease as they will inherit the recessive allele from the mother and the Y chromosome from the father, although there is a 50% probability of inheriting the wild type allele from the mother.

Now if the mother is suffering from the disease i.e. has the recessive allele on both the X chromosome while the father is healthy having no allele for the disease, the daughters will always be a carrier but never suffer from the disease as they eill inherit the healthy wild type allele from the father as one X chromosome comes from the father and the other X chromosome from the mother. The sons will however all suffer from the disease as they inherit the Y chromosome from the father and the X chromosome having the recessive allele causing the disease will be inherited from the mother.

Now suppose the mother is a carrier i.e. carries the recessive allele only on one X chromosome but the father suffers from the disease making his genotype XrY (Xr denoting recessive allele carrying X chromosome), then, 50%of their son will duffer from the disease while 50% of the daughters will also have a chance of suffering from the disease.

If both the parents do not have a single recessive X linked disease gene on any of their X chromosome then none of the children will suffer from the disease.

About phenotype of parents- If the mother is a carrier i.e. have the diseased allele on only one X Chromosome, then the phenotype of mother will be normal. But the father can never be a carrier for a X linked recessive disease as males have only one X chromosome. If the diseased allele in present on that X chromosome in males it will be expressed as there is no dominant healthy wild type allele to dominate the diseased gene. Thus if the father has the recessive diseased allele on X chromosome, the father\'s phenotype will be expresding the disease while if the father do not have the allele he will be healthy. On the other hand for the mother to express the disease the recessive allele has to be present on bith her X chromosome.

Probability of offsprings showing the trait- If mother is a carrier and father is normal, then 50% son suffering from the disease while 50% son will be normal. 50% daughters will be carrier and 50%daughters will be normal without any diseased allele. The carrier females will also be phenotypically normal.

If mother is a carrier and father is suffering from the disease, 50%don will duffer from the disease while 50%will be normal. Among daughters 50% will be normal without any diseased allele and 50% will be suffering from the disease.

If mother is suffering from the disease and father is healthy then both the sons will suffer from the disease while daughters will all be carriers.

If both parents are suffering from the disease all their children will inherit the disease. If none of the parents have any recessive Xlinked diseased gene then neither one of their children will suffer from the disease nor will any children be a carrier for the disease.