Final answer:
Option (b), A rare recessive trait is more likely to appear when closely related individuals mate, as their offspring may inherit two copies of the recessive allele, expressing the trait.
Step-by-step explanation:
A rare recessive trait is more likely to appear in a pedigree when two people who are closely related mate. This is because if both parents carry the recessive allele, there is an increased chance that their offspring will inherit two copies of the recessive allele and therefore express the recessive trait. Individuals with a recessive trait must be homozygous for that trait, meaning they have two copies of the recessive allele. In contrast, individuals with a dominant trait might be either homozygous or heterozygous for the trait.
Sex-linked recessive traits are typically more common in males than females, as males have only one X chromosome. A female must have two copies of a recessive allele on the X chromosome to express the trait, while a male only needs one copy since the Y chromosome does not have a second allele to mask the effect of the recessive allele found on the X chromosome.
Therefore, the answer is 'b) recessive' because a recessive trait is more likely to be expressed when consanguinity occurs, meaning the mating between two genetically related individuals increases the chance of offspring being homozygous recessive for a trait.