Recombination frequency can be calculated based on crosses.

Recombination Frequency:
Recombination frequency is a measure of the genetic distance between two genes or genetic markers on a chromosome. It represents the likelihood of a crossover event occurring between two loci during meiosis. The recombination frequency is expressed as a percentage and can range from 0% to 50%.

Explanation:
When two genes or genetic markers are located close to each other on a chromosome, they have a higher chance of being inherited together. This is because during meiosis, homologous chromosomes can undergo crossover events, where genetic material is exchanged between non-sister chromatids. However, if the two genes are located far apart, the chances of a crossover event occurring between them are higher.

By performing crosses and analyzing the offspring, researchers can determine the recombination frequency between two genes. Crosses involve mating individuals that are heterozygous for different alleles at the desired loci. The offspring are then analyzed to determine the frequency at which recombinant phenotypes are observed.

To calculate the recombination frequency, the number of recombinant offspring is divided by the total number of offspring and multiplied by 100. This gives the percentage of recombinant offspring. The recombination frequency reflects the genetic distance between the two genes or markers, with higher frequencies indicating a greater distance.

Importance:
Recombination frequency is a fundamental concept in genetics and is used to map the positions of genes on chromosomes. By determining the recombination frequencies between different genes, geneticists can construct genetic maps that show the relative positions of genes on a chromosome. This information is crucial for understanding inheritance patterns, gene linkage, and genetic diseases.

Conclusion:
Based on crosses, recombination frequency can be calculated to determine the genetic distance between genes or genetic markers on a chromosome. This information is important for studying inheritance patterns and constructing genetic maps. Therefore, the correct answer to the question is option B: Recombination frequency.