Suppose Condition A is an autosomal recessive
trait that affects the nervous system. In one family,
the father, mother, daughter, and elder son do not
have Condition A, but the younger son has
Condition A. Both of the individuals in which of the
following pairs MUST be carriers of the Condition A
allele?
A. Father and elder son
B. Mother and daughter
C. Daughter and elder son
D. Mother and father