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Problem 21b
An organism of the genotype AaBbCc was testcrossed to a triply recessive organism (aabbcc). The genotypes of the progeny are presented in the following table.
Answer part (a) again, assuming the three genes are so tightly linked on a single chromosome that no crossover gametes were recovered in the sample of offspring.
Problem 21c
An organism of the genotype AaBbCc was testcrossed to a triply recessive organism (aabbcc). The genotypes of the progeny are presented in the following table.
What can you conclude from the actual data about the location of the three genes in relation to one another?
Problem 22
Based on our discussion of the potential inaccuracy of mapping, would you revise your answer to Problem 22? If so, how?
Problem 23
In Creighton and McClintock’s experiment demonstrating that crossing over involves physical exchange between chromosomes, explain the importance of the cytological markers (the translocated segment and the chromosome knob) in the experimental rationale.
Problem 24
DNA markers have greatly enhanced the mapping of genes in humans. What are DNA markers, and what advantage do they confer?
Problem 25
Are mitotic recombinations and sister chromatid exchanges effective in producing genetic variability in an individual? in the offspring of individuals?
