Final answer:
The fragile site on chromosome 3 is indicated by the short arm, known as 'p'. In human karyotypes, autosomes are organized by size and the p and q arms are indicative of their relative lengths, with specific loci designated numerically.
Step-by-step explanation:
The fragile site on the autosomal chromosome is represented by the short arm or "p" of chromosome 3. In a human karyotype, autosomes are arranged from largest to smallest, with chromosome 1 being the largest and chromosome 22 being the smallest, not counting the X and Y chromosomes which are not autosomes. Chromosome arms, which project from either end of the centromere, are designated as short (p) or long (q), and the arms are further divided and denoted by numbers for specific loci.