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The pattern of methylation of germ cells is established in each sex during gametogenesis. This takes place in two steps. In males, the methylation pattern develops in two stages: first, the methylation pattern that is characteristic of mature sperm is established in the spermatocyte. Further changes in the pattern are made during fertilization. In females, […]
DNA methylation occurs at specific sites. In bacteria, the DNA methylation is used for identifying bacterial restriction-methylation system that is involved in phage defence and is also used for distinguishing replicated and non-replicated DNA. In eukaryotes, the DNA methylation is connected with the control of transcription. The methylation of a control region is usually accompanied […]
Polycomb group (PcG) proteins perpetuate a state of repression of genes through cell division. The polycomb responsive element (PRE) is a DNA sequence that is required for the action of PcG. The PRE provides a nucleation centre from which PcG proteins propagate an inactive structure. The trithorax group (trxG) proteins antagonize the action of PcG. […]
Euchromatin and heterochromatin can be localized during the interphase in the nucleus. Heterochromatin is highly inert and condensed, transcriptionally repressed, replicates during the late S-phase and is found in the periphery of the nucleus. Centromeric heterochromatin predominantly consists of satellite DNAs. When a gene is transferred to a position adjacent to the heterochromatin, it may […]
Epigenetics is the study of heritable changes in gene expression or cellular phenotype that is caused by mechanisms that do not involve changes in DNA sequence. In practice, epigenetics is the study of gene expression or phenotype changes. The Greek word ‘epi’ means over, above or outer and the word genetics means study of genes. […]
rDNA technology has gained importance in each and every aspect of modern biological researches. The rDNAs are used in basic research or in the commercial production of useful products. rDNA also find application in agriculture and industry. In Pharmaceutical Industry Important compounds such as recombinant insulin, which are used in the treatment of diabetes, human […]
Genomic Library It is a collection of clones containing every single gene present in an organism. For the construction of a genomic library, the entire genomic DNA is isolated from host cells/tissues, purified and broken randomly into fragments of appropriate size for cloning into suitable vector. DNA can be fragmented by physical shearing or by […]
Cells all of which contain the same DNA sequences are called ‘clones’. Cloning serves two main purposes. The various steps involved in molecular cloning can be outlined in the following sections. Preparation of Vector DNA Vector DNAs that originate from microorganisms are propagated and harvested from their appropriate microbial hosts. The bacterial cells grown in […]
This is used to visualize the position of a cloned gene on a eukaryotic chromosome. The cells are treated with a fixative. They are attached to a glass slide and incubated with RNAse and NaOH to degrade RNA and denature the DNA. The chromosome exposes the segments of DNA. A sample of the cloned gen […]
If DNA is denatured and later allowed to renature, the two separated single strands of DNA will zipper back to reform the double-stranded DNA molecule. This ability of the complementary sequences to anneal or to hybridize one another is called ‘nucleic acid hybridization’. This technique helps in determining the gene structure and in identifying molecules […]