Explain what the term gene mutation means.
Rickets is a childhood disorder in which bones become soft and weak. It is usually the result of a shortage of vitamin D, calcium ions or phosphate ions. A rare type of rickets that cannot be treated successfully with vitamin D therapy is caused by a mutant allele on the X chromosome. Fig. 6.1 shows a pedigree chart for a family with a history of this condition. Using the symbols $X^R$ for the mutant allele on the X chromosome and $X^r$ for the non-mutant allele on the X chromosome, state the genotypes of the following individuals: 1 3 9 10
This mutation is in a gene that encodes a protein located in the cells of the proximal convoluted tubule of the kidney. That protein takes part in phosphate ion transport across membranes. Suggest why people with this mutant allele show symptoms of rickets.