The notion that DNA or RNA is the genetic information for the most species has been confirmed and reinforced by the accompanying scientific proof of are series of DNA tests:
Direct evidence
Indirect evidence.
Direct Evidence:
Pneumococcus transformation:
Transformation exchanges or transfers genetic information (recombination) from one bacterial strain to another without direct contact. Frederick Griffith was the first to identify the transformation process in 1928. Griffith’s effect was the name given to this phenomenon. Griffith’s experiment indicated transformation, but he could not remember the transforming principle.
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Pneumococci strains have a genetic variation, which the presence of distinct phenotypes may recognize. Griffith began his research with two pneumococci strains that were phenotypically distinct.
They create two types of colonies when cultivated artificially on nutrient agar medium:
Smooth
rough.
The polysaccharide capsule is necessary for virulence because it protects the bacterial cell from leucocyte phagocytosis. However, stain cells lack this capsule, resulting in dull, rough (R) colonies. Because such stains cannot cause pneumonia, they are referred to as avirulent.
DNA as a Transforming Principle:
Avery, Macleod, and McCarthy used experiments to show that DNA was the transforming principle. When DNA extract from type IIS pneumococci was combined with type IIR pneumococci in vitro, they discovered that some pneumococci were changed to type III S.
However, DNA extract from type III S may be contaminated with a few molecules of proteins and RNA. This contaminating protein and RNA might cause type II R to type III S transformation. So, utilizing a bacterial culture system and specialized enzymes that break down DNA, RNA, and protein, Avery, Macleod, and McCarthy presented the most conclusive experiment.
The Hershey-Chase Experiment:
In 1952, A. D. Hershey and M. Chase demonstrated yet another direct evidence that DNA is the genetic material. They started by looking at the life cycle of T2 bacteriophages in E. coli. T2 bacteriophages have a protein-based hexagonal box-like head coat and tail. The proteinaceous skull covering is jam-packed with DNA.
Hershey and Chase discovered that the phage’s DNA entered the host cell during bacteriophage replication, but most of the protein head and tail remained outside the cell. As a result, it’s safe to assume that DNA includes the genetic information required for viral proliferation.
Indirect Evidence:
Some indirect evidence has been used to support the idea that DNA is the genetic material of higher organisms:
Localization:
The genetic material should be in a specific cell area. The genes are unable to operate correctly if they have no stable position. It is well understood that DNA, as a gene substance, is always found principally within the chromosome of the eukaryotic cell’s nucleus. This approach has demonstrated that DNA is wholly contained within the chromosome and is the most critical component of chromosomes.
Stability:
The cell’s many macromolecules are constantly being analyzed and catabolized. However, this is undesirable for a genetic material holding vital hereditary information. The genetic function will be lost if this occurs. DNA is the most metabolically stable macromolecule in the cell.
Mutagen Sensitivity:
The genetic material contains mutations, which are a common occurrence. Mutagens are substances capable of causing mutations. Mutagens include UV-rays, X-rays, y-rays, and various chemical substances. Mutagens create a change in the structure of a gene when they are applied to an organism’s cells.
Gene mutations involve variations in the quantity and order of nucleotides, as genes are DNA segments. Breaks in the DNA molecule are sometimes caused by mutation. Changes in DNA structure eventually reflect changes in the hereditary nature of the organism. As a result, the susceptibility of DNA to mutagens provides indirect proof that DNA is the genetic material.
DNA Composition:
The link between DNA content determined by 24-hour DNA tests and the number of chromosomal sets is one of the most noticeable aspects of the genetic material. According to several quantitative measurement techniques, diploid cells have twice as much DNA as haploid cells of the same species.
Tetraploid and octoploid cells, on the other hand, contain four times and eight times the DNA of haploid cells, respectively. Even the DNA content of sperm cells is linked to the same or different tissues of various organisms. As a result, and according to different types of DNA tests, the behavior of DNA and chromosome is similar, implying that DNA is the genetic material.
