Question

Queen Victoria of England was born from two parents that did not carry alleles for hemophilia. However, a random mutation occurred causing her to become a carrier. Why does this pedigree indicate an X- linked recessive pattern of inheritance?

Answer 1

Answer: The random mutation occurred causing   Queen Victoria to become a carrier. Alexis, the son of the last czar of Russia, inherited the allele ultimately from Queen Victoria, who was the grandmother of his mother Alexandra. The mode of transmission of the disease through unaffected carrier females which shows a pattern of X-linked recessive inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be always expressed in males who are necessarily homozygous for the gene mutation because they have one X and one Y chromosome and in females who are homozygous for the gene mutation because they have one mutated X chromosome and one normal X chromosome so females with one copy of the mutated gene act as carriers.