Final answer:
An individual in the alien species has three parents, each contributing 12 chromosomes. Therefore, the total number of autosomal chromosomes possessed by an individual alien is 30.
Step-by-step explanation:
An individual in the alien species has three parents, each contributing 12 chromosomes. The sex of each alien is determined by 6 sex chromosomes. Therefore, the total number of autosomal chromosomes possessed by an individual alien would be:
Number of autosomal chromosomes = Total number of chromosomes - Number of sex chromosomes
Number of autosomal chromosomes = 36 chromosomes - 6 sex chromosomes
Number of autosomal chromosomes = 30 chromosomes
Therefore, the correct answer is D) 30.