Show Advanced Search


Containing Text
- - -
Filter by author or institution
Filter by publication date
October, 2006
Filter by journal section

Filter by science education

Germ Cells: The reproductive cells in multicellular organisms at various stages during Gametogenesis.

Transgenic Organisms

JoVE 10809

Transgenic organisms are genetically engineered to carry transgenes—genes from a different species—as part of their genome. The transgene may either be a different version of one of the organism’s genes or a gene that does not exist in their genome. Transgenes are usually generated by recombinant DNA and DNA cloning techniques. Transgenic bacteria, plants, and animals allow scientists to address biological queries and design practical solutions. Scientists begin the process of transgenesis—introducing a transgene into an organism’s genome—by selecting an appropriate technique. There are several biological, chemical, and physical methods of transgenesis. A common biological method involves the virus-mediated introduction of foreign DNA into a host cell genome, called transduction. A popular chemical method uses calcium phosphate (Ca3(PO4)2). The method is based on the formation of a Ca3(PO4)2/DNA precipitate to facilitate DNA binding to and entering cells. Physical methods such as microinjection—a technique that uses a thin, glass needle to manually insert genetic material into cells—artificially introduce DNA by force. Once inside the cell, a transgene can either integrate randomly or at a specific site in the genome with the help of DNA repa

 Core: Biology

Replication in Eukaryotes

JoVE 10789

In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before cell division, so there are many proteins that fill specialized roles in the replication process. Replication occurs in three phases: initiation, elongation, and termination, and ends with two complete sets of chromosomes in the nucleus.

Eukaryotic replication follows many of the same principles as prokaryotic DNA replication, but because the genome is much larger and the chromosomes are linear rather than circular, the process requires more proteins and has a few key differences. Replication occurs simultaneously at multiple origins of replication along each chromosome. Initiator proteins recognize and bind to the origin, recruiting helicase to unwind the DNA double helix. At each point of origin, two replication forks form. Primase then adds short RNA primers to the single strands of DNA, which serve as a starting point for DNA polymerase to bind and begin copying the sequence. DNA can only be synthesized in the 5’ to 3’ direction, so replication of both strands from a single replication fork proceeds in two different directions. The leading strand is synthesized continuously, while the lagging strand is synthesized in short stretches 100-200 base pairs in length, called Okazaki fragments. Once the bu

 Core: Biology

Crossing Over

JoVE 10769

Unlike mitosis, meiosis aims for genetic diversity in its creation of haploid gametes. Dividing germ cells first begin this process in prophase I, where each chromosome—replicated in S phase—is now composed of two sister chromatids (identical copies) joined centrally.

The homologous pairs of sister chromosomes—one from the maternal and one from the paternal genome—then begin to align alongside each other lengthwise, matching corresponding DNA positions in a process called synapsis. In order to hold the homologs together, a protein complex—the synaptonemal complex—forms. The synaptonemal complex facilitates the exchange of corresponding random pieces of DNA between non-sister chromatids, yielding new combinations of alleles via homologous recombination. As the synaptonemal complex begins to dissolve, X-shaped structures hold the homologous chromosomes together until recombination is completed. The structures—called chiasmata—mark the areas where crossover of genetic information occurred.

 Core: Biology

C. elegans Development and Reproduction

JoVE 5110

Ceanorhabditis elegans is a powerful tool to help understand how organisms develop from a single cell into a vast interconnected array of functioning tissues. Early work in C. elegans traced the complete cell lineage and structure at the electron microscopy level, allowing researchers unprecedented insight into the connection between genes, development and disease. …

 Biology I

Drosophila Larval IHC

JoVE 5106

Immunohistochemistry (IHC) is a technique used to visualize the presence and location of proteins within tissues. Drosophila larvae are particularly amenable to IHC because of the ease with which they can be processed for staining. Additionally, the larvae are transparent, meaning that some tissues can be visualized without the need for dissection.

In IHC, proteins are…

 Biology I

Automated Quantification of Hematopoietic Cell – Stromal Cell Interactions in Histological Images of Undecalcified Bone

1Immunodynamics, German Rheumatism Research Center, a Leibniz Institute, 2Biophysical Analytics, German Rheumatism Research Center, a Leibniz Institute, 3Max-Delbrück Center for Molecular Medicine, 4Wimasis GmbH, 5Immunodynamics and Intravital Imaging, Charité - University of Medicine

JoVE 52544

 Developmental Biology

Polysome Profiling in Leishmania, Human Cells and Mouse Testis

1Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, 2Department of Biological Sciences, Texas Tech University, 3CISER (Center for the Integration of STEM Education & Research), Texas Tech University

JoVE 57600


Injecting Gryllus bimaculatus Eggs

1Colby College, 2Division of Evolutionary Developmental Biology, National Institute for Basic Biology, 3Department of Biological Sciences, National University of Singapore, 4Department Biology and Department of Neuroscience, Bowdoin College, 5Department of Organismic and Evolutionary Biology and Department of Molecular and Cellular Biology, Harvard University

JoVE 59726

 Developmental Biology

Assessment of Sexual Behavior of Male Mice

1Department of Psychiatry and Mental Health Institute of the Second Xiangya Hospital, Central South University, National Clinical Research Center on Mental Disorders and National Technology Institute on Mental Disorders, Hunan Key Laboratory of Psychiatry and Mental Health, 2Research Center for Pharmacology & Toxicology, Institute of Medicinal Plant Development (IMPLAD), Chinese Academy of Medical Sciences and Peking Union Medical College, 3Department of Social Medicine and Health Management, Xiangya School of Public Health, Central South University

Video Coming Soon

JoVE 60154

 JoVE In-Press
More Results...