Quiz 6: Genetic Linkage and Mapping in Eukaryotes
Reproduction is an important phenomenon in living organisms, through which they multiply and maintain their life form. The most vital is in keeping the genetic lineage from generation to generation. During this process, the physical characters are transmitted from parents to offspring through genetic material (di-deoxy nucleic acid-DNA). In case of bacterium, this process can be completed naturally and artificially. The natural process of genetic transfer is by three ways: 1. Conjugation 2. Transduction 3. Transformation The similarities and differences between these mechanisms are explained below:
Each bacterium got different nutritional requirements to survive. That's why in-vitro , different media are prepared for different microorganisms. Organic compounds, like vitamins play an important role in cellular functions. Most of vitamins are often synthesized by bacteria. Due to mutation, this property of synthesizing vitamins is hampered. As a result, certain vitamin, which bacteria cannot produce, is supplemented into growing media. Such bacterium that cannot survive on minimal media is known as auxotroph. In an experiment, two bacteria with double ( met - bio - thr + leu + thi + ) and triple ( met + bio + thr - leu - thi - ) mutations has taken. When grown individually on media lacking methionine and biotin for double mutated bacteria and threonine, leucin and thiamine lacking media for triple mutated bacteria, it was observed that there are no bacterial colonies formed on the plate. When bacterial mixture is mixed well, it was observed that bacterial colonies are formed indicating that bacteria that are grown, had the ability to synthesize methione ( met + ), biotin ( bio + ), threonine ( thr + ), leucine ( leu + ), and thiamine ( thi + ). This explains that there is an exchange of genetic material between these bacteria. As a result, mutated bacteria became normal by acquiring characters from other bacteria. Later on this experiment explained the phenomenon of conjugation. In this, genetic material between bacteria is exchanged through physical contact by forming sex pili or conjugating bridgE.
Genetic analysis is an important phenomenon for the genetic makeup of an organism. This helps in finding the arrangement of genes on chromosomes and to know the functionality of these. Some of the advantages of bacteria and bacteriophages for genetic amalysis are: 1. They multiply rapidly by asexual mode of reproduction and generate large number of new bacteria and viruses. 2. Their genetic material is small in sizE.3. They can be grown easily in laboratory. 4. Methodology to isolate bacteria and phages are available. To alter gene arrangement of these microorganisms is quite a simpler way. 5. During the experiments, mutant species are easily detected with the help specific media or plaque formation. Gene is a coding sequence present on genetic material of an organism. Some time single gene can code for single character, or group of genes can contribute for single physical character. In cluster of genes, many genes can have same or different sequence but have same function. The other form of gene is known as allele. Bacteria: 1. The arrangement of genes on bacterial chromosome are seems to be in linear fashion. 2. They also include allele present on plasmid. Plasmid is an extrachromosomal material present in bacterial cytoplasm, which consists of several genes required for antibiotic resistance and DNA replication. 3. The alleles show complementation effect, through which single mutated gene is complemented by another normal genE.Bacteriophage 1. The genetic material of bacteriophage can accommodate 1-2% of bacterial chromosomE.2. The genes show homoallelic mutation. 3. The genes are arranged in such a way that intragenic mapping is possible by deletion mapping.