Final answer:
Lod scores are used to determine the probability that two genes are linked. They are calculated by comparing the observed data against the expected data if genes were to assort independently, and high LOD scores indicate genetic linkage between genes.
Step-by-step explanation:
Lod (logarithm of odds) scores are used to determine the probability that two genes are linked. A LOD score is a statistical measure that tests whether two genes are likely to be located near each other on a chromosome and thus inherit together during meiosis, indicating linkage. When observing genetic crosses, geneticists can examine the frequency of recombination events between different genes to infer their relative positions on a chromosome.
Genes that are close together have a lower frequency of recombinant offspring compared to parental types. LOD scores capitalize on this by comparing the likelihood of observing the data if the genes are linked to the likelihood if they are unlinked; a high LOD score suggests linkage.
According to Sturtevant's work, genes can be mapped on chromosomes based on their recombination frequencies. He proposed using centimorgans (cM) as the unit of measure in a genetic map, where a recombination frequency of 0.01 corresponds to 1 cM. Recombination frequencies lower than 0.50 indicate linkage because the genes tend to be inherited together rather than assorting independently
The use of LOD scores is not related to the interference among genes, the chi-square test for independence, the configuration of alleles in terms of repulsion or coupling, or the exact number of progeny expected from a genetic cross. Instead, LOD scores specifically address whether there is a statistical likelihood that two genes are located near each other on the same chromosome and are therefore genetically linked.