Two parents of normal phenotype have a son with an autosomal recessive linked genetic disorder. what is the most likely cause of this? a. both parents must be heterozygous for the disorder, or carriers. b. because most of a human's genes are autosomal, it was never noticed that the parents had the condition. c. because the condition is on the x chromosome and the child only has one copy of the x. d, some environmental effect in the womb caused the child to express the disorder.