Concept explainers
When the interrupted mating technique was used with five different strains of Hfr bacteria, the following orders of gene entry and recombination were observed. On the basis of these data, draw a map of the bacterial chromosome. Do the data support the concept of circularity?
To draw: A map for bacterial chromosome.
Introduction: The bacterial chromosome is transferred during the process of conjugation, which leads to genetic recombination. The genetic recombination provides data for mapping.
Answer to Problem 1NST
Pictorial representation: The sequence of genes are arranged as contigs, and their overlapping is shown in fig 1.
Fig 1: Overlapping of the contigs of the Hfr strains.
Pictorial representation: The chromosomal map of bacteria
Explanation of Solution
The transfer of chromosome is strain specific. It also depends on where and in which orientation in the chromosomes the F factor has integrated.
In interrupted mating, there is difference in the time of gene transfer. Some may be transferred earlier while other are transferred late. In strain 2 and 4, the common sequence is MB. In strain 1 and 3, CHRO is common, and HRO is the repetitive sequence.
To determine: Whether the given data support the concept of circularity.
Introduction: A single bacterial chromosome contains most of the DNA of the bacteria. Mapping the bacterial chromosomes provides information regarding the position of various genes.
Explanation of Solution
Contigs are the continuous set of overlapping DNA segments. These segments represent a particular region of the DNA. In the given figure, the end overlaps each other. In two strains the order is reversed which means the orientation of the transfer is reversed. By the overlapping of the contigs in the given strains, the map that will be constructed is TCHROMBAK. All the genes are linked together to give a map. The ends overlap indicates that the map is circular. When all these chromosomes are arranged in the form of a map, they form a circular map.
Thus, the map constructed that will be constructed from the given Hfr strains is TCHROMBAK. The overlap ends indicate that the map is circular.
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Chapter 6 Solutions
Concepts of Genetics (12th Edition)
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