A、Genetic recombination of alleles is associated with physical exchange between chromosomes.
B、Genes are located on chromosomes and the map distance between them could often be measured by the number of nucleotides in the DNA.
C、Determining map distances in humans could be done by using pedigrees and calculating lod scores.
D、Association studies allow genes that have no obvious phenotype to be accurately mapped.
E、Crossing over does not occur in male Drosophila, so there is no genetic recombination.