Genetics: From Mendel’s Laws to the Central Dogma

Genetics, the study of heredity and variation, has significantly advanced from Gregor Mendel’s foundational work on inheritance laws to modern DNA technology. Mendel’s laws of inheritance laid the groundwork for understanding the chromosomal and molecular basis of genetics. Key concepts such as the DNA double helix, the role of RNA, the Central Dogma of molecular biology, and DNA profiling have deepened our understanding of genetic information flow and its practical applications in fields like medicine, forensics, and evolutionary biology.

Mendel’s Laws

About: Mendel is known as the father of genetics. He worked on the pea plants and proposed the fundamental laws of inheritance. These are:

1. Law of Dominance: States that when two different genes controlling for the same character come together in an organism, only one is expressed, and this expressed gene is known as the dominant gene. 
2. Law of Independent Assortment: Separate genes for separate traits are passed independently of one another from parents to offspring; genes do not influence each other with regard to the sorting of alleles into gametes.
3. Law of Segregation: States that a diploid organism passes a randomly selected allele for a trait to its offspring, such that the offspring receives one allele from each parent. 
   1. According to the law of segregation, only one of the two gene copies present in an organism is distributed to each gamete (egg or sperm cell) that it makes, and the allocation of the gene copies is random. 
   2. When an egg and a sperm join in fertilisation, they form a new organism whose genotype consists of the alleles contained in the gametes.

Flow of Genetic Information: From DNA to Proteins

Central Dogma states that the genetic information flows from DNA to RNA to Protein.

• DNA Replication: DNA replication is the process by which DNA makes a copy of itself during cell division.
• Transcription: The process by which a cell makes an RNA copy of a piece of DNA. This RNA copy, called messenger RNA (mRNA), carries the genetic information needed to make proteins in a cell.
• Translation: The process by which a cell makes proteins using the genetic information carried in messenger RNA (mRNA). The mRNA is made by copying DNA, and the information it carries tells the cell how to link amino acids together to form proteins.

Genetic code

• Background:The process of translation requires the transfer of genetic information from a polymer of nucleotides to synthesise a polymer of amino acids.
  • This led to the proposition of a genetic code that could direct the sequence of amino acids during the synthesis of proteins.

• About: The genetic code is a set of rules defining how the four-letter code of DNA is translated into the 20-letter code of amino acids, which are the building blocks of proteins.
• The genetic code is a set of three-letter combinations of nucleotides called codons, each of which corresponds to a specific amino acid or stop signal.
  • For example: The RNA sequence UUU specifically coded for the amino acid phenylalanine.
  • 3 Codons in Humans are Stop Codon: UGA, UAA, and UAG.
• There are 64 possible permutations, or combinations, of three-letter nucleotide sequences that can be made from the four nucleotides.
• Of these 64 codons, 61 represent amino acids, and three are stop signals.

Conclusion

From Mendel’s foundational laws to the intricacies of the genetic code, genetics has unlocked the secrets of inheritance and protein synthesis. The Central Dogma elucidates the flow of genetic information, guiding our understanding of DNA replication, transcription, and translation, paving the way for transformative discoveries in medicine and biotechnology.

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