What is the difference between the classical concept and the modern concept of genes?

The concept of the gene has evolved from a simple unit of heredity to a complex molecular entity. During Mendel's time, genes were understood only through the inheritance of physical traits. This formed the classical concept. With the discovery of DNA, its double helix structure and the development of molecular biology, the gene is now defined by its chemical structure and functional properties. This is known as the modern concept.

For understanding the difference between the classical and modern concept of genes, the following criteria are used:

1. Based on Definition or Concept

Classical Concept: Gene was defined as an abstract unit of heredity responsible for controlling a single trait. It was known through breeding experiments and inheritance patterns.

Modern Concept: A gene is a segment of DNA that contains the information to produce a functional product, either a protein or an RNA. It is both a structural and functional unit of heredity.

2. Based on Structure

Classical Concept: Genes were imagined as tiny particles or "beads" arranged linearly on chromosomes. No internal structure was known.

Modern Concept: Genes have a complex structure. They include coding regions (exons), non-coding regions (introns), promoter sequences, enhancers, silencers and terminators.

3. Based on Function

Classical Concept: Each gene was believed to affect only one character or trait. The relationship was simple and one-to-one.

Modern Concept: A gene may code for multiple proteins due to alternative splicing. One gene can influence several traits (pleiotropy) and multiple genes can control a single trait (polygenic inheritance).

4. Based on Mutation

Classical Concept: Mutation was described as a sudden change in a trait, without knowing what exactly changed inside the gene.

Modern Concept: Mutation is a change in the nucleotide sequence of DNA. It can be precisely studied and classified into types like point mutation, deletion, insertion, frameshift etc.

5. Based on Location and Mapping

Classical Concept: Genes were located through breeding experiments and crossing over data. Mapping was rough and symbolic.

Modern Concept: Genes are located using molecular tools. The exact position, sequence and length of a gene on the chromosome can be determined.

6. Based on Gene Expression and Regulation

Classical Concept: No clear idea about how genes were turned on or off. Regulation was not well understood.

Modern Concept: Gene expression is well studied. Transcription and translation are controlled by regulatory sequences, transcription factors, epigenetic modifications and environmental factors.

7. Based on Gene Interaction

Classical Concept: Genes were thought to act independently. Interaction was only known through phenotypic ratios.

Modern Concept: Gene networks and interactions are well studied. Concepts like epistasis, co-dominance, incomplete dominance and gene silencing are explained at molecular level.







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