Dna is the Genetic Material
Sutton and Boveri, in 1902, proposed that the genetic information passed between generations by way of chromosomes. But it took many years to clarify whether the genetic material was the DNA or the protein of the chromosomes. Both have the structural diversity as great as expected of the genetic material.
1. Protein.
Originally (until 1940s), the
proteins were thought to play the role of
the genetic material
because they are macromolecules that show
enormous variety due to various combinations
of
their 20 constituent amino acids, and exhibit great
specificity of function. However,
they have no mechanism
for duplication. Hence, they do not qualify
to act as the genetic material.
2. DNA. DNA, deoxyribonucleic acid, also shows a wide structural variety, because the four types of nucleotide units it is composed of, may be arranged in an endless manner in its molecules. It also fulfils all the requirements of the genetic material listed above. It has now been experimentally proved that DNA is the genetic material.
It is found in all the cells.
All the somatic cells of a given species contain the same amount of DNA, and this is double the amount found in the gamete cells.
It exhibits infinite variety due to unlimited sequences its monomers can occur in.
It duplicates its genetic information by faithful replication during interphase.
DNA copies are precisely distributed to the daughter cells during mitosis.
It develops mutation (inheritable variation) in the genes and chromosomes occasionally.
It stores genetic information as a triplet code.
DNA expresses its genetic information by transcription of mRNA and synthesis of proteins. The proteins contribute to the structure of the cells, and, by acting as enzymes, they control metabolic activities in the cells.
Different genes remain functional in different cell types so that the latter may acquire their specific structure and functions. This differential gene activity is the key to differentiation.
DNA governs the various life stages, viz., embryonic development, growth, sexual maturity and old age, at proper times as if it has a biological clock.
DNA is able to repair itself, if damaged, to preserve the genetic information.
DNA absorbs the same wavelengths of high-energy radiation that cause maximum mutations.
The above properties of DNA make it fit to act as the genetic material.
DNA (deoxyribonucleic acid) is the most celebrated molecule of present time because it is the substance of inheritance. Mendel's hereditary factors and Morgan's genes are, in fact, composed of DNA. The DNA is the nature's unique molecule in that it directs its own replication. The resemblance of offspring to their parents results from the precise replication of parental DNA and transfer of replicated molecules to the offspring. Reported in 1868 by Friedrich Miescher, DNA is now known even to a layman.