Final answer:
Using recombination frequencies, the most likely gene order on a chromosome is determined to be a-b-c-d, considering their respective genetic distances and frequencies.
Step-by-step explanation:
When determining the order of genes on a chromosome using recombination frequencies, we look for the smallest frequencies which typically represent closer genetic proximity. For the given recombination frequencies between genes a and b (0.1), b and c (0.3), c and d (0.5), a and d (0.1), and a and c (0.4), the most likely order that accommodates these frequencies is a-b-c-d. This is reasoned by aligning the genes such that their recombination frequencies make sense, with smaller frequencies indicating closer proximity and the largest (0.5 between c and d) suggesting the most distance.
Based on the frequencies provided, genes a and b must be close due to their low recombination frequency. Similarly, a and d must also be close, which is consistent with b being between a and c and a and d having a low recombination frequency as well. Therefore, gene c must be further from gene a than gene b is, which corresponds with a higher recombination frequency of 0.4. The final answer, reflecting the relative positions from left to right on the chromosome, is a-b-c-d.