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October, 2006
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Gene Library: A large collection of DNA fragments cloned (Cloning, Molecular) from a given organism, tissue, organ, or cell type. It may contain complete genomic sequences (Genomic library) or complementary DNA sequences, the latter being formed from messenger RNA and lacking intron sequences.

Recombineering and Gene Targeting

JoVE 5553

One of the most widely used tools in modern biology is molecular cloning with restriction enzymes, which create compatible ends between DNA fragments that allow them to be joined together. However, this technique has certain restrictions that limit its applicability for large or complex DNA construct generation. A newer technique that addresses some of these shortcomings…


Replication of the Ordered, Nonredundant Library of Pseudomonas aeruginosa strain PA14 Transposon Insertion Mutants

1Department of Pediatrics, Mucosal Immunology and Biology Research Center, Massachusetts General Hospital, 2Department of Molecular Biology, Massachusetts General Hospital, 3Department of Genetics, Harvard Medical School, 4Department of Pediatrics, Harvard Medical School

JoVE 57298

 Immunology and Infection

Hardy-Weinberg & Genetic Drift- Concept

JoVE 10559

Evolutionary change is interesting and important to study, but changes in populations occur over long periods of time and in huge physical spaces and are therefore very difficult to measure. In general, studying phenomena like this requires the use of mathematical models which are built using parameters that can be conveniently measured. These models are then used to make predictions about how …

 Lab Bio

Genetics of Organisms- Concept

JoVE 10557

Mendelian Genetics

Evolution is caused by changes in the genetic composition of populations. In the field of population genetics, scientists model this process as changes in the frequency of alleles at individual genetic loci. This simple representation of how evolution occurs dates to Gregor Mendel’s analysis of trait inheritance patterns in pea plants, first presented in 1865.…

 Lab Bio


JoVE 10817

Genome editing technologies allow scientists to modify an organism’s DNA via the addition, removal, or rearrangement of genetic material at specific genomic locations. These types of techniques could potentially be used to cure genetic disorders such as hemophilia and sickle cell anemia. One popular and widely used DNA-editing research tool that could lead to safe and effective cures for genetic disorders is the CRISPR-Cas9 system. CRISPR-Cas9 stands for Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated protein 9. A basic CRISPR-Cas9 system consists of a Cas9 endonuclease and a small RNA that guides Cas9 to the target DNA. CRISPR sequences were first observed in bacteria and later identified in archaea. Researchers discovered that the CRISPR-Cas9 system serves an adaptive immune defense against invading viruses. Many bacteria and most archaea capture short sequences of the viral DNA to create a library of virus DNA segments, or CRISPR arrays. When the prokaryotes are re-exposed to the same virus or class of viruses, CRISPR arrays are used to transcribe small RNA segments that help recognize viral invaders and subsequently destroy viral DNA with Cas9 or a similar endonuclease. CRISPR-Cas9 is commonly used in the laboratory to remove DNA and insert a new DNA sequence in its place. To achieve this, researchers must first c

 Core: Biology

Evolutionary Relationships- Concept

JoVE 10561

Humans have been attempting to properly classify living things since Aristotle made the first attempt during the 4th century BC. Aristotle’s system was improved upon during the Renaissance and then, subsequently, by Carolus Linnaeus in the mid 1700’s. These more formal classification and organization systems grouped species by their physical similarity to one another. For example,…

 Lab Bio


JoVE 5548

Among different methods to evaluate gene expression, the high-throughput sequencing of RNA, or RNA-seq. is particularly attractive, as it can be performed and analyzed without relying on prior available genomic information. During RNA-seq, RNA isolated from samples of interest is used to generate a DNA library, which is then amplified and sequenced. Ultimately, RNA-seq can …


Complementary DNA

JoVE 10818

Only genes that are transcribed into messenger RNA (mRNA) are active, or expressed. Scientists can, therefore, extract the mRNA from cells to study gene expression in different cells and tissues. The scientist converts mRNA into complementary DNA (cDNA) via reverse transcription. Because mRNA does not contain introns (non-coding regions) and other regulatory sequences, cDNA—unlike genomic DNA—also allows researchers to directly determine the amino acid sequence of the peptide encoded by the gene. cDNA can be generated by several methods, but a common way is to first extract total RNA from cells, and then isolate the mRNA from the more predominant types—transfer RNA (tRNA) and ribosomal (rRNA). Mature eukaryotic mRNA has a poly(A) tail—a string of adenine nucleotides—added to its 3’ end, while other types of RNA do not. Therefore, a string of thymine nucleotides (oligo-dTs) can be attached to a substrate such as a column or magnetic beads, to specifically base-pair with the poly(A) tails of mRNA. While mRNA with a poly(A) tail is captured, the other types of RNA are washed away. Next, reverse transcriptase—a DNA polymerase enzyme from retroviruses—is used to generate cDNA from the mRNA. Since, like most DNA polymerases, reverse transcriptase can add nucleotides only to the 3’ end of a chain, a pol

 Core: Biology
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