Final Answer:
The steps for using a three-factor cross to map genes in the correct order are as follows:
1) Cross two true-breeding strains that differ in three traits
2) Analyze the phenotypes of the offspring
3) Determine the recombination frequency between the three traits
4) Map the genes based on the recombination frequencies
5) Perform a test cross with a trihybrid individual
Step-by-step explanation:
The initial step involves crossing two true-breeding strains differing in three traits, setting the groundwork by producing heterozygous offspring for all three traits. Following this, analyzing the phenotypes of the offspring becomes pivotal. This process assists in identifying the linkage relationships among the three genes and establishes the parental phenotypes, forming a foundation for further analysis.
After phenotype analysis, calculating the recombination frequency between the three traits is crucial. Recombination frequency is determined by the number of recombinant offspring divided by the total number of offspring, multiplied by 100 to yield a percentage. For instance, if out of 1000 offspring, 50 exhibit recombination between traits A and B, the RF between A and B is calculated as 50/1000 x 100 = 5%.
Once recombination frequencies are established, the genes can be mapped based on these frequencies. Higher recombination frequencies imply greater distance between traits on the chromosome, while lower frequencies indicate closer proximity. Finally, performing a test cross with a trihybrid individual helps verify the gene order obtained from mapping, ensuring accuracy in establishing the arrangement of genes along the chromosome. This comprehensive process aids in understanding gene linkage and order through the analysis of recombination frequencies in three-factor crosses.