DNA Structure & Human Genome Sequencing — NEET Biology
📚 Practice ConceptIn the last section, the essentials of human genome sequencing and its consequences will also be discussed. Let us begin our discussion by first understanding the structure of the most interesting molecule in the living system, that is, the DNA. In subsequent sections, we will understand that why it is the most abundant genetic material, and what its relationship is with RNA.
Which of the following statements concerning the organization and function of the human genome are NOT correct? S1: The vast majority of the human genome, specifically less than 2%, is composed of non-coding sequences like introns and repetitive DNA. S2: Repetitive DNA sequences, though lacking direct coding functions, are crucial for understanding chromosome structure, dynamics, and evolutionary patterns. S3: Single Nucleotide Polymorphisms (SNPs) are variations occurring in non-coding regions of DNA and are utilized in genetic mapping. S4: All genes in the human genome consist of continuous coding sequences (exons) without any interspersed non-coding regions. S5: The "central dogma" of molecular biology explains that genetic information flows exclusively from DNA to RNA to protein, with no exceptions in any living system.
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Correct answer: B — S1, S4 and S5
This question evaluates the understanding of human genome features and fundamental molecular biology principles. S1: This statement is NOT correct. Less than 2% of the human genome codes for proteins, meaning the vast majority (more than 98%) is composed of non-coding sequences. The statement reverses this proportion, making it incorrect. S2: This statement is correct. Repetitive sequences are indeed thought to have no direct coding functions but shed light on chromosome structure, dynamics, and evolution. S3: This statement is correct. SNPs (Single Nucleotide Polymorphisms) are single-base DNA differences primarily found in non-coding regions, and this information is used for genetic mapping and tracing human history. S4: This statement is NOT correct. In eukaryotes, genes often have a 'split-gene' arrangement, where coding sequences (exons) are interrupted by non-coding intervening sequences (introns). Thus, not all genes consist of continuous coding sequences. S5: This statement is NOT correct. While the central dogma (DNA to RNA to protein) holds true for most organisms, there are exceptions, such as in some viruses where information flows in reverse (RNA to DNA), a process known as reverse transcription. Therefore, statements S1, S4, and S5 are NOT correct.
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