81. A novel enzyme was Identified in humans. The followingapproaches are available to identify the chromosome on which the gene encoding the enzyme is present:
(A) Suppress the activity of enzyme by RNAi.
(B) Identify polymorphism in the population and carry out pedigree analysis to study its inheritance.
(C) Purify the enzyme, decipher Its amino acid sequence, predict its DNA sequence and search for its presence in the available human genome sequence.
(D) Create chromosome addition lines by making somatic hybrids between human and mouse cells, identify lines showing the enzyme activity and the human chromosome present in it.
Which of the above approaches can be used?
(1) (A) or (B) (2) (B) or (C)
(3) (C) or (D) (4) (A) or (C)
Detailed Solution Explanation for Chromosome Identification Approaches
The question asks which of the given approaches can be used to identify the chromosome on which the gene encoding a novel human enzyme is located. The options involve different molecular genetics and cytogenetic techniques.
Analysis of Each Approach
(A) Suppress the activity of enzyme by RNA interference (RNAi):
RNAi is a method to silence gene expression post-transcriptionally by degrading specific mRNA. This is useful for studying gene function by observing phenotypic effects after gene knockdown. However, RNAi does not provide information about the physical chromosomal location of the gene. It only tells about the gene’s function and effect, not its chromosomal position.
(B) Identify polymorphism in the population and carry out pedigree analysis to study inheritance:
Polymorphisms (variations in DNA sequence) linked to the enzyme gene can be tracked in families to observe inheritance patterns. Pedigree analysis can suggest linkage to a chromosomal region based on co-segregation of polymorphic markers and the trait. This is a classical linkage mapping approach, which can hint at gene location on chromosomes but generally requires genetic markers related to the gene.
(C) Purify the enzyme, decipher its amino acid sequence, predict its DNA sequence, and search for its presence in the available human genome sequence:
This is a direct molecular approach. By sequencing the protein and predicting the coding gene sequence, one can perform a database search (e.g., against the human genome) to find the exact chromosomal position of the gene encoding the enzyme. This method directly identifies the gene’s physical location on a chromosome.
(D) Create chromosome addition lines by making somatic hybrids between human and mouse cells, identify lines showing enzyme activity, and the human chromosome present in it:
Somatic cell hybridization is a classical technique for gene mapping. By fusing human cells with mouse cells and analyzing which hybrids retain human chromosomes and enzyme activity, the specific human chromosome that carries the gene can be pinpointed.
Which methods can be used?
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RNAi (A) cannot localize chromosome position.
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Polymorphism and pedigree analysis (B) can be used for linkage but require polymorphic markers and family data, so it is a valid indirect method for chromosome localization.
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Sequence-based identification (C) is a direct and precise method for locating the gene’s chromosome position.
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Somatic hybridization (D) is also a valid method to assign a gene to a chromosome.
The correct pairs are thus:
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(C) or (D) — Both are physical or cytogenetic gene mapping methods that directly identify the chromosome for the gene.
Other pairings involving RNAi (A) are not appropriate for chromosome identification. Pedigree analysis (B) is indirect and not as precise as (C) or (D).
Answer: (3) (C) or (D)
Introduction
Identifying the chromosomal location of a novel gene, such as one encoding a newly discovered enzyme, is a fundamental step in genetics. Different molecular and cytogenetic methods allow researchers to map genes to specific chromosomes. This article explains the key approaches including protein sequencing, genome database searches, somatic cell hybridization, and linkage analysis with polymorphisms.
Detailed Explanation
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Protein Sequencing and Genome Search:
Purifying the enzyme and deciphering its amino acid sequence allows prediction of its DNA coding sequence. Researchers can then search this sequence in the human genome database to precisely locate its chromosomal position. This method is direct and highly accurate for gene mapping. -
Somatic Cell Hybridization:
By creating hybrids of human and mouse cells that contain various human chromosomes, scientists can detect enzyme activity in these hybrids. The presence of activity correlates with the human chromosome in the hybrid cells, enabling assignment of the gene’s location to a specific chromosome. -
Polymorphism and Pedigree Analysis:
Studying genetic polymorphisms in populations and tracking these markers through family pedigrees can reveal linkage of the gene to certain chromosomal regions. This indirect method traces inheritance patterns that hint at chromosome location. -
RNA Interference (RNAi):
While RNAi can suppress gene expression and reveal gene function, it does not provide information about the gene’s chromosomal location and hence is not suitable for gene mapping.
This explanation clarifies why the best approaches for chromosome identification of a gene encoding a novel enzyme are (C) and (D), combining modern molecular biology and classical genetics techniques.
