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Modern Genetic Analysis Answers to Selected Problems
Chapter 12*

1.

a. The sequence is 2 1 3 (or 3 1 2).
b. YAC A spans at least a part of both 1 and 3. YAC B is within region 1. YAC C spans at least a part of regions 1 and 2. YAC D is contained within region 2. YAC E is contained within region 3. A diagram of these results is shown here. In the diagram, there is no way of knowing the exact location of the ends of each YAC.
See question

3.

The cross is

A parental type will have the genotype of either strain and be in a majority, whereas a recombinant type will have a mixed genotype and be in a minority of the ascospores. Clearly, the first two ascospore types are parental, with the remaining being recombinant.

a. The cys-1 locus is in this region of chromosome 5. If it were not in this region, linkage to either of the RFLP loci would not be observed.
b. The entire region is approximately 17 m.u. in length.
c. A suitable next step in cloning cys-1 might be to do PFGE to obtain a pure sample of chromosome 5, followed by cloning of chromosome fragments. The clones could be screened by the RFLP probes.
See question

5. | Remember that a gene is one small region of a long strand of DNA and that a cloned gene will contain the entire sequence of the gene under normal circumstances. If there are two cuts within a gene, three fragments will be produced, all of which will interact with the probe, as was seen with enzyme 1. Cuts external to a gene will produce one fragment that will interact with the probe, which was seen with enzyme 2. One cut within a gene will produce two fragments that will interact with the probe, as was seen with enzyme 3. See question

8.

a. RAPDS are formed by being bracketed by two inverted copies of the primer sequence. In the diagram shown here, the primer is indicated by X's, and the amplified region is within brackets. For convenience, the two amplified regions are placed on the same lengthy piece of DNA for strain 1.

Strain 2 lacks one or two regions complementary to the primer.

b. Progeny 1 and 6 are identical with the strain 1 parent. Progeny 4 and 7 are identical with the strain 2 parent. Progeny 2 and 5 received the chromosome holding the upper band from the strain 1 parent and the chromosome holding the lower band from the strain 2 parent (resulting in no second band). Progeny 3 received the opposite: the chromosome holding the lower band from the strain 1 parent and the chromosome holding the upper band from the strain 2 parent (resulting in no second band). Therefore, bands 1 and 2 are unlinked.
See question

9. | a. Gene x is located in region 5. b. The location of gene y is region 8. c. Both probes are able to hybridize with cosmid E because cosmid E is long enough to contain part of genes x and y. See question

13.

a. DNA from each individual was obtained. It was restricted, electrophoresed, blotted, and then probed with the five probes. After each probing, an autoradiograph was produced.
b. The RFLP locus closest to the disease allele is 4°.
c. With the use of the probe for RFLP 4, the disease gene can be cloned by positional cloning (see description of cloning the cystic fibrosis gene as an example).
See question

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