Three-point mapping solution The best way to solve these problems is to develop a systematic approach. First, determine which of the genotypes are the parental genotypes. The genotypes found most frequently are the parental genotypes.From the table it is clear that the ABCand abcgenotypes were the parental genotypes. Next we need to determine the order of the genes. Once we have determined the parental genotypes, we use that information along with the information obtained from the double-crossover. The double-crossover gametes are always in the lowest frequency.From the table the ABcand abCgenotypes are in the lowest frequency. The next important point is that a double-crossover event moves the middle allele from one sister chromatid to the other. This effectively places the non-parental allele of the middle gene onto a chromosome with the parental alleles of the two flanking genes. We can see from the table that the Cgene must be in the middle because the recessive c
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