Edward was found to be heterozygous (Ss) for sickle-cell trait. The alleles represented by the letters S and s are a. linked. b. on homologous chromosomes. c. both present in each of Edward's sperm cells. d. on the same chromosome but far apart.

Verified step by step guidance

1. Understand the meaning of heterozygous: Edward having heterozygous sickle-cell trait (Ss) means he has two different alleles for the sickle-cell gene, one normal (S) and one mutated (s).
2. Recognize the location of alleles: Alleles are located on chromosomes, and in a diploid organism like humans, each individual has two copies of each chromosome, one from each parent.
3. Identify the relationship between alleles and chromosomes: Since Edward is heterozygous, each allele (S and s) is located on one of the two homologous chromosomes. Homologous chromosomes are pairs of chromosomes that have the same genes at the same loci but possibly different alleles.
4. Consider the distribution of alleles in gametes: During meiosis, homologous chromosomes separate, and each gamete (sperm cell in males) receives one of the two chromosomes. Thus, each of Edward's sperm cells will contain either the S allele or the s allele, but not both.
5. Eliminate incorrect options based on the above understanding: The alleles are not linked (always inherited together), not both present in each sperm cell, and not on the same chromosome but far apart. The correct answer is that the alleles are on homologous chromosomes.