Question

How is the hereditary information in DNA coded and passed from generation to generation?

Answer 1

The mechanism of coding and passing of hereditary information in DNA from one generation to the next is very complex. The hereditary information in DNA is present in the form of sequence patterns of bases.

Complete answer:
The sequences of bases present in DNA act as a language that can be read by the cellular machinery. The four bases adenine, guanine, cytosine, and thymine are linked in a definite manner, i.e., A always links to the T and G always links to the C, and vice versa. While DNA stores the genetic information, RNA helps in its transfer. The process of transfer of DNA into RNA is known as transcription, and then RNA is converted into protein by the process of translation. Translation is a complex process and requires transfer of genetic information to amino acids.

The coding is done in groups of three bases known as codon. The information which is stored in the codon can either code for an amino acid or code for instruction for the fate of proteins formed by the amino acids. When three out of the four bases form a codon, then it would generate ${{4}^{3}}$ i.e., 64 codons. Out of these 64, 61 code for amino acids, and the other three act as stop codons as they do not code for any amino acid. An initiator codon AUG starts the coding, and ends with the termination sequence. tRNA is an adaptor molecule used for translation. tRNA attaches with the amino acid on one of its ends, and pairs with mRNA on the other. In this way, the chain continues when tRNA attaches with the next amino acid.

As there are 23 pairs of chromosomes in humans, the transfer of DNA becomes even more complicated. In eukaryotic cells, the chromosomes are packed in specific protein complexes and then transferred to the next generation through specialized cells known as gametes. In this way, the genetic information is coded and transferred from generation to generation.

Note: As gametes are fused during fertilization, it is important to maintain the chromosome number. Therefore, the chromosomes in the gametes are halved so that after fusion, the number of chromosomes remain consistent.