Mixed together met- blo- thr * leu thit and met* blo * thr- leu- thi- met- blo- thr leu thi met * bio + thr-leu- thi- 10 cells 10 cells 10 cells Nutrient agar plates lacking amino acids, blotin, and thlamine No colonies Bacterlal colonles No colonies Experiment of Lederberg and Tatum demonstrating genetic transfer during conjugation in E. coli. When plated on a growth medium lacking amino acids, biotin, and thiamine, the met- bio- thr+ leu+ thi+ and met+ bio+ thr- leu- thi- strains were unable to grow. However, if the two strains were mixed together and then plated, some colonies were observed. These colonies were due to the transfer of genetic material between these two strains by conjugation. Note: In bacteria, it is common to give genes a three-letter name (shown in italics) that is related to the function of the gene. A plus superscript (+) indicates a functional gene, and a minus superscript (-) indicates a mutation that has caused the gene or gene product to be inactive. In some cases, several genes have related functions. These may have the same three-letter name followed by different capital letters. For example, different genes involved with leucine biosynthesis may be called leuA, leuB, leuc, and so on. In the experiment described here, the genes involved in leucine biosynthesis were not distinguished, so the gene is simply referred to as leu+ (for a functional gene) and leu- (for a nonfunctional gene).
Genetic Recombination
Recombination is crucial to this process because it allows genes to be reassorted into diverse combinations. Genetic recombination is the process of combining genetic components from two different origins into a single unit. In prokaryotes, genetic recombination takes place by the unilateral transfer of deoxyribonucleic acid. It includes transduction, transformation, and conjugation. The genetic exchange occurring between homologous deoxyribonucleic acid sequences (DNA) from two different sources is termed general recombination. For this to happen, an identical sequence of the two recombining molecules is required. The process of genetic exchange which occurs in eukaryotes during sexual reproduction such as meiosis is an example of this type of genetic recombination.
Microbial Genetics
Genes are the functional units of heredity. They transfer characteristic information from parents to the offspring.
In the experiment of Figure shown, Lederberg and Tatum could not
discern whether met+ bio+ genetic material was transferred to the
met− bio− thr+ leu+ thi+ strain or if thr+ leu+ thi+ genetic material
was transferred to the met+ bio+ thr− leu− thi− strain. Let’s suppose
that one strain is streptomycin-resistant (say, met+ bio+ thr− leu−
thi−) and the other strain is sensitive to streptomycin. Describe an
experiment that could determine whether the met+ bio+ genetic
material was transferred to the met − bio− thr+ leu+ thi+ strain or
the thr+ leu+ thi+ genetic material was transferred to the met+ bio+
thr− leu− thi− strain. bio+ thr− leu− thi− strain.
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