A female is heterozygous for an X-linked recessive trait. Which of the following statements is true? She may or may not be affected because some of her cells express one allele of the causative gene, while other cells express the other allele. She is unaffected because all of her cells express the common allele of the causative gene. She is affected because all of her cells express the disease allele of the causative gene. She is unaffected because all of her cells express both alleles of the causative gene..