Molecular Marker

Molecular Marker

Which pair of markers are used to study both structure and function?

Functional and structural genomics require complementary marker resources for integrated analysis. Expressed Sequence Tags derived from cDNA provide evidence of actively expressed genes, enabling functional annotation, tissue-specific expression profiling and identification of conserved coding regions for comparative mapping. Variable Number Tandem Repeats and related tandem repeat families reveal chromosome architecture, heterochromatin organization, high polymorphism and linkage relationships for structural mapping. Combining VNTR for structural diversity assessment and EST for gene function investigation bridges genome architecture with gene content, supporting both structural and functional studies.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

A STR on X chromosome shows unexpected allele. Likely cause:

X chromosome transmission shows characteristic patterns: sons receive X from mother, daughters receive X from both parents. STR allele unexplained by maternal or paternal haplotypes suggests new mutation altering repeat number rather than SNP interference or VNTR artifact. Microsatellite mutation rate is elevated due to replication slippage, generating novel alleles in germline. Maternal inheritance explains expected allele but not unexpected size variant. Therefore appearance of atypical X-linked STR allele most plausibly results from de novo mutation expanding or contracting repeat tract within X locus.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

Which polymorphism is caused by replication slippage?

Mechanism of polymorphism generation differs among markers. Short Tandem Repeats arise from DNA polymerase slippage during replication where nascent strand misaligns on template in repetitive tract, adding or deleting few repeat units. This slippage model explains high mutation rate of microsatellites and multiallelic length variation. RFLP results from point mutation affecting restriction site, SNP from single nucleotide substitution, ISSR from amplification between microsatellite loci. Replication slippage specifically underlies STR variation, supporting use in population genetics where high variability is advantageous.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

Which of the following is noncoding and highly repeated?

Genomic composition includes low-copy coding sequences and high-copy repetitive fractions with distinct functions. Satellite DNA comprises tandemly repeated, noncoding sequences organized as large continuous arrays at centromeres, telomeres and constitutive heterochromatin, further subdivided into microsatellite, minisatellite and macrosatellite classes based on repeat unit length. Highly reiterated and largely transcriptionally inert, it contributes to centromere function, heterochromatin formation and chromosome segregation fidelity. SNPs are single-base variants, exons are coding regions, ESTs represent transcribed tags. Noncoding reiterated organization defines satellite DNA distinction from low-copy functional sequences.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

Which repeat is found in telomeric regions?

Repetitive DNA localization reflects functional specialization of chromosome domains. Minisatellites, classified as VNTRs with 10-100 bp units, frequently cluster in subtelomeric and terminal regions, contributing to telomere stability, recombination hotspots and chromosome pairing during meiosis. Macrosatellites also reside at centromeres and heterochromatic blocks. SSRs and STRs, representing microsatellites with 1-6 bp motifs, are interspersed throughout euchromatin rather than enriched at ends. Preferential accumulation of minisatellite arrays near telomeres supports their structural role in maintaining chromosome integrity and regulating recombination frequency.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

Which DNA-based marker is best for high-throughput genotyping?

High-throughput genotyping demands markers that are extremely abundant, evenly distributed across chromosomes, biallelic, easily automated and suitable for multiplexed detection in parallel reactions. Single Nucleotide Polymorphisms fulfill these requirements with occurrence every few hundred bases, amenable to array-based chips, next-generation sequencing and fluorescence-based assays producing millions of genotypes rapidly with minimal DNA input. SSR, VNTR and RAPD rely on gel electrophoresis and manual allele sizing, limiting throughput and automation. SNP platforms offer cost-effective scalable screening for association studies and genomic selection programs.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

In STR inheritance, which offspring inherits both alleles from parents?

Codominant STR markers reveal both maternal and paternal alleles in offspring. In a family where each parent possesses two distinct alleles, child inherits one allele from each parent, producing combined genotype containing contributions from both parental pairs. Some offspring may inherit particular combinations like one specific paternal and one maternal allele. Analyzing band patterns, individuals labeled A, B, D show both parental contributions present, demonstrating Mendelian segregation. This transmission pattern confirms heterozygosity and codominant expression essential for linkage mapping, forensics and parentage studies.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

Which technique allows SNP typing without radioisotopes?

Early SNP genotyping relied on radioactive allele-specific oligonucleotide hybridization and autoradiography with safety concerns and limited throughput. Modern SNP chip or microarray technology immobilizes thousands to millions of synthetic oligonucleotide probes on solid surface, labeling target DNA with fluorescent dyes, enabling massively parallel genotyping without radioisotopes. Differential hybridization signal intensity distinguishes homozygous and heterozygous genotypes automatically. RFLP traditionally required radiolabeled probes, RAPD and VNTR need electrophoresis. Microarray platforms provide automated, safe, high-throughput non-radioactive typing essential for genome-wide association studies and personalized medicine.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

Which pedigree analysis reveals late-onset disease using RFLP?

Late-onset genetic disorders show phenotype only after certain age, complicating early pedigree analysis because at-risk individuals may appear unaffected. RFLP markers tightly linked to disease gene allow tracking of disease haplotype before clinical onset. Age-specific penetrance models incorporate probability of developing disease by certain age, enabling risk calculation using marker co-segregation in families. Early-childhood mapping applies to pediatric disorders, X-linked inheritance pattern is not specific, SNP hybridization is genotyping method. Combining linkage data with age-dependent penetrance improves predictive accuracy for counseling.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

STRs used in parentage testing differ based on:

Short Tandem Repeats exhibit polymorphism due to variation in number of tandemly repeated core units at a locus. DNA polymerase slippage adds or deletes repeat units during replication, generating alleles differing in length but not necessarily base composition, methylation state or expression level. Parentage testing exploits highly polymorphic allele length variation; child inherits one allele length from each parent. Base composition and epigenetic modifications do not determine STR genotype. Counting repeat number provides quantifiable allelic diversity crucial for forensic identity and kinship resolution.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

Which mutation type affects restriction enzyme recognition sites?

Restriction endonucleases recognize specific palindromic tetra- to octanucleotide sequences and introduce double-strand breaks at those sites. A single nucleotide polymorphism within recognition motif abolishes existing site or creates new site, altering fragment lengths after digestion, which appears as restriction fragment length polymorphism on gels. For example, sickle cell GAG to GTG mutation destroys MstII site. VNTR and STR polymorphisms involve tandem repeat copy number, not restriction recognition changes, while ESTs represent transcribed sequences. Therefore SNPs commonly provide molecular basis for RFLP variation and linkage studies.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Molecular Marker

Which of the following are codominant markers?

Marker inheritance mode determines informativeness. Codominant markers allow differentiation of homozygote and heterozygote, displaying both alleles in heterozygote. Simple Sequence Repeats are multiallelic codominant, with each allele visible as distinct band length. Single Nucleotide Polymorphisms are biallelic codominant, heterozygote shows both nucleotides. RAPD, ISSR and AFLP generate dominant profiles where presence denotes dominant allele, absence recessive, preventing heterozygote distinction. RFLP is also codominant but pairing SSR with SNP represents most widely used codominant combination for linkage mapping, diversity analysis and molecular breeding applications.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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