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#genetic sequences

2 public questions tagged with this topic.

MOLECULAR EVOLUTION

Which sequence is best for molecular clock studies?

Molecular evolution studies changes in DNA, RNA and proteins over time. Neutral theory by Kimura proposes most molecular substitutions are neutral and fixed by drift at rate equal to mutation rate, explaining molecular clock constancy where synonymous mutations accumulate steadily. Mitochondrial DNA maternally inherited and pseudogenes evolving faster due to lack of constraint provide markers for phylogeny. Purifying selection removes deleterious variants. Therefore Cytochrome c illustrates principle of molecular evolution and neutral processes. This concept integrates genetics, ecology and molecular evidence, frequently tested in NEET, GATE and CSIR-NET, highlighting links between genotype, phenotype and environment.

Ref: Nei & Kumar, Molecular Evolution, Clocks and Purifying Selection.

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Molecular Marker

Which repeat type is >100 base pairs?

Tandem repetitive DNA is classified by repeat unit length and array size. Microsatellites, SSR or STR, contain 1-6 bp motifs, minisatellites or VNTR contain 10-100 bp motifs, while macrosatellites exceed 100 bp and can span kilobases, forming large heterochromatic blocks at centromeres, telomeres and heterochromatic regions. The greater than 100 base pair definition distinguishes macrosatellite organization, which often shows higher-order repeat structure, epigenetic silencing and copy number variation. Such large repeats are unsuitable for standard PCR microsatellite assays but crucial for chromosome structure and large-scale genomic variation 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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