Final answer:
As two- and three-factor testcrosses can be used to measure recombination frequencies, identify gene order on chromosomes, and determine interference in crossover events, which are all key aspects in the study of genetics.
The correct option is d) All of the above.
Step-by-step explanation:
In addition to determining genotypes, two- and three-factor testcrosses can be used for multiple purposes. As testcrosses are used for: a) Measuring recombination frequencies between genes, b) Identifying gene order on a chromosome, and c) Determining interference in crossover events.
Recombination frequencies can be measured by observing the proportion of offspring that exhibit nonparental genotypes, which indicates the physical distance between genes on a chromosome. By comparing these frequencies, geneticists can map the genes' relative positions, a process known as genetic mapping. The phenomenon of interference, which refers to the non-randomness of crossover events, can also be assessed through testcrosses, giving insight into the complex mechanics of genetic recombination and chromosome behavior.
The correct answer to this question is d) All of the above,