Final answer:
Mendel's unit factors in pairs are two alleles on paternal and maternal homologs, representing genes on homologous chromosomes.
Step-by-step explanation:
Mendel's unit factors in pairs are most accurately known to be two alleles on paternal and maternal homologs. Gregor Mendel's experiments and observations led him to deduce that hereditary factors are transmitted as discrete units, which we now know as genes. These genes, or alleles, are located on homologous chromosome pairs. In the case of a single gene that has a dominant-recessive pattern, the presence of different alleles (dominant and recessive) can result in organisms with the same phenotype but different genotypes - such as the F1 heterozygous offspring which resembled one of the parents more than the other due to the expression of the dominant allele over the recessive allele.