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October, 2006
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Genetic Variation: The phenotypic and genotypic differences among individuals in a population.

Mutation, Gene Flow, and Genetic Drift

JoVE 10964

In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size). The original sources of genetic variation are mutations, which are changes in the nucleotide sequence of DNA. Mutations create new alleles and increase genetic variability. Most mutations do not cause significant changes to the health or functioning of an organism. However, if a mutation reduces the chances of survival, the organism may die before reproducing. Therefore, such harmful mutations are likely to be eliminated by natural selection. Individuals in natural populations may also select their mates based on certain characteristics, and thus do not reproduce randomly. In this case, alleles for the traits that are selected against will become less frequent in the population. Furthermore, populations can experience gene flow, the transfer of alleles into and out of gene pools, due to migration. A classic example of gene flow is observed in most baboon species. Female baboons mate most frequently with dominant males in a troop. Juvenile ma

 Core: Biology

Artificial Selection- Concept

JoVE 10555

Natural Selection and Adaptive Evolution

In natural settings, adaptive evolution takes place by natural selection, a process in which differences in traits lead to differences in survival and reproductive success between individuals. This happens because individuals with certain phenotypes have a higher probability of survival and/or produce more surviving offspring than individuals with …

 Lab Bio

What is Population Genetics?

JoVE 10962

A population is composed of members of the same species that simultaneously live and interact in the same area. When individuals in a population breed, they pass down their genes to their offspring. Many of these genes are polymorphic, meaning that they occur in multiple variants. Such variations of a gene are referred to as alleles. The collective set of all the alleles within a population is known as the gene pool. While some alleles of a given gene might be observed commonly, other variants may be encountered at a much lower frequency. Gene pools are not static. The frequency and occurrence of alleles in a gene pool may change over time. For instance, allele frequencies change due to random mutations, natural selection, migration, and chance. Population genetics examines genetic variation within and between populations, and changes in allele frequencies across generations. Population geneticists use mathematical models to investigate and predict allele frequencies in populations. The gene pools of natural populations may vary significantly. One goal of population genetics is to determine genetic variation among different populations of the same species. Studying such variations has implications for species health, domestication, management and conservation. For instance, increased urbanization gradually fragments natural landscapes and leads to h

 Core: Biology

Hardy-Weinberg Principle

JoVE 10963

Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype. In the early 20th century, scientists wondered why the frequency of some rarely-observed dominant traits did not increase in randomly-mating populations with each generation. For example, why does the dominant polydactyly trait (E, extra fingers and/or toes) not become more common than the usual number of digits (e) in many animal species? In 1908, this phenomenon of unchanged genetic variation across generations was independently demonstrated by a German physician, Wilhelm Weinberg, and a British Mathematician, G. H. Hardy. The principle later became known as Hardy-Weinberg equilibrium. The Hardy-Weinberg equation (p2 + 2pq + q2 = 1) elegantly relates allele frequencies to genotype frequencies. For instance, in a population with polydactyly cases, the gene pool contains E and e al

 Core: Biology

SNP Genotyping

JoVE 5544

Single nucleotide polymorphisms, or SNPs, are the most common form of genetic variation in humans. These differences at individual bases in the DNA often do not directly affect gene expression, but in many cases can still be useful for locating disease-associated genes or for diagnosing patients. Numerous methodologies have been established to identify, or…


Yeast Reproduction

JoVE 5097

Saccharomyces cerevisiae is a species of yeast that is an extremely valuable model organism. Importantly, S. cerevisiae is a unicellular eukaryote that undergoes many of the same biological processes as humans. This video provides an introduction to the yeast cell cycle, and explains how S. cerevisiae reproduces both asexually and sexually Yeast reproduce asexually …

 Biology I

Bacterial Transformation

JoVE 10982

In 1928, bacteriologist Frederick Griffith worked on a vaccine for pneumonia, which is caused by Streptococcus pneumoniae bacteria. Griffith studied two pneumonia strains in mice: one pathogenic and one non-pathogenic. Only the pathogenic strain killed host mice.

Griffith made an unexpected discovery when he killed the pathogenic strain and mixed its remains with the live, non-pathogenic strain. Not only did the mixture kill host mice, but it also contained living pathogenic bacteria that produced pathogenic offspring. Griffith concluded that the non-pathogenic strain received something from the dead pathogenic strain that transformed it into the pathogenic strain; he called this the transforming principle. At the time of Griffith’s studies, there was heated debate surrounding the identity of the genetic material. Much early evidence implicated proteins as the hereditary molecules. Griffith’s experiments on bacterial transformation provided some of the earliest data demonstrating that DNA is the genetic material. Bacteria incorporate external DNA through transformation. Transformation occurs naturally but is also induced in laboratories—often to clone DNA. To clone a specific gene, scientists can insert the gene into a plasmid, a circular DNA molecule that can independently replicate. The plasmid often contains an antib

 Core: Biology

Limits to Natural Selection

JoVE 11000

Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.

For one, natural selection can only act upon existing genetic variation. Hypothetically, red tusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for red tusks, natural selection cannot increase the prevalence of red tusks. The allele must first exist or arise through mutation. Tradeoffs also limit natural selection. While an allele for red tusks may protect against poaching, it might also make tusks brittle and less useful for fighting and foraging. Tradeoffs at the genomic level exist because natural selection acts upon individuals rather than alleles. Neighboring genes on the same chromosome are often linked and inherited together. If an allele for red tusks is passed on with an allele causing infertility, red tusks could disappear because the inherited combination does more harm than good.  Intermediate traits can also constrain natural selection. Imagine an elephant population with three variants of tusks: traditional, red tusks, and an intermediate rose. The rose tusks may be coveted by poachers, like t

 Core: Biology

Mismatch Repair

JoVE 10791

Organisms are capable of detecting and fixing nucleotide mismatches that occur during DNA replication. This sophisticated process requires identifying the new strand and replacing the erroneous bases with correct nucleotides. Mismatch repair is coordinated by many proteins in both prokaryotes and eukaryotes.

The human genome has more than 3 billion base pairs of DNA per cell. Prior to cell division, that vast amount of genetic information needs to be replicated. Despite the proofreading ability of the DNA polymerase, a copying error occurs approximately every 1 million base pairs. One type of error is the mismatch of nucleotides, for example, the pairing of A with G or T with C. Such mismatches are detected and repaired by the Mutator protein family. These proteins were first described in the bacteria Escherichia coli (E. coli), but homologs appear throughout prokaryotes and eukaryotes. Mutator S (MutS) initiates the mismatch repair (MMR) by identifying and binding to the mismatch. Subsequently, MutL identifies which strand is the new copy. Only the new strand requires fixing while the template strand needs to remain intact. How can the molecular machinery identify the newly synthesized strand of DNA? In many organisms, cytosine and adenine bases of the new strand receive a methyl group some time after replication. Therefore,

 Core: Biology

What is Biodiversity?

JoVE 10950

Biodiversity describes the variety of living things at multiple organizational levels: genetic, species and ecosystem diversity. Species diversity includes all branches of the evolutionary tree from single-celled prokaryotic organisms, bacteria, and archaea, to the eukaryotic kingdoms: plants; animals; fungi; and protists. To date, there have been about 1.75 million species identified, and new species are discovered every week. Biodiversity also includes the interactions that connect organisms to each other and to the environment in which they live. Organisms have evolved together to create the intricate webs of life that involve both cooperative (symbiotic) relationships and predator-prey relationships. Biodiversity is, therefore, a much broader concept than the simple collection of species to which it is often reduced. All living things depend on the existence and activities of other living things. Groups of populations of different species interacting with one another and with their physical environment constitute an ecosystem. Ecosystems themselves are very diverse: for example forests, ponds, deserts, coral reefs, and even the human intestinal flora. Scientists who study biodiversity are not only interested in the number of different species in an ecosystem, but also in how many individuals of each species is present. Studying biodiversity indicates in w

 Core: Biology

Transformation of E. coli Cells Using an Adapted Calcium Chloride Procedure

JoVE 10515

Source: Natalia Martin1, Andrew J. Van Alst1, Rhiannon M. LeVeque1, and Victor J. DiRita1
1 Department of Microbiology and Molecular Genetics, Michigan State University

Bacteria have the ability to exchange genetic material (DeoxyriboNucleic Acid, DNA) in a process known as horizontal gene transfer. Incorporating exogenous DNA…


Screening for Functional Non-coding Genetic Variants Using Electrophoretic Mobility Shift Assay (EMSA) and DNA-affinity Precipitation Assay (DAPA)

1Center for Autoimmune Genomics and Etiology, Cincinnati Children's Hospital, 2Medical Scientist Training Program, University of Cincinnati, 3Immunology Graduate Program, University of Cincinnati, 4Divisions of Biomedical Informatics and Developmental Biology, Cincinnati Children's Hospital

JoVE 54093


Targeted Next-generation Sequencing and Bioinformatics Pipeline to Evaluate Genetic Determinants of Constitutional Disease

1Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, 2Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, 3Analytic and Translational Genetics Unit, Center for Genomic Medicine, Harvard Medical School, Massachusetts General Hospital, Stanley Centre for Psychiatric Research, Broad Institute of MIT and Harvard, 4Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, 5School of Medicine, Faculty of Health Sciences, Queen's University, 6Faculty of Medicine, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 7CHEO Research Institute, Faculty of Medicine, University of Ottawa, 8Department of Clinical Neurological Sciences, Western University, 9Division of Neurology, Department of Medicine, Sunnybrook Health Sciences Centre, University of Toronto, 10Division of Neurology, Department of Medicine, University of Toronto, 11Morton and Gloria Shulman Movement Disorders Centre, Toronto Western Hospital, 12Department of Clinical Neurological Sciences, Schulich School of Medicine and Dentistry, Western University, 13Parkwood Institute, St. Joseph's Health Care, 14Department of Medicine, Division of Neurology, McMaster University, 15Division of Neurology, Department of Medicine, Baycrest Health Sciences, 16Canadian Partnership for Stroke Recovery Sunnybrook Site, Sunnybrook Health Science Centre, University of Toronto

JoVE 57266


Quantitation and Analysis of the Formation of HO-Endonuclease Stimulated Chromosomal Translocations by Single-Strand Annealing in Saccharomyces cerevisiae

1Irell & Manella Graduate School of Biological Sciences, 2Department of Molecular and Cellular Biology, City of Hope Comprehensive Cancer Center and Beckman Research Institute, 3Department of Biochemistry and Molecular Biology, University of Southern California, Norris Comprehensive Cancer Center

JoVE 3150


In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila

1Department of Molecular and Human Genetics, Baylor College of Medicine, 2Program in Developmental Biology, Baylor College of Medicine, 3Department of Pediatrics, Section of Neurology and Developmental Neuroscience, Baylor College of Medicine, 4Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, 5Department of Neuroscience, Baylor College of Medicine

JoVE 59658


Navigating MARRVEL, a Web-Based Tool that Integrates Human Genomics and Model Organism Genetics Information

1Program in Developmental Biology, Baylor College of Medicine, 2Medical Scientist Training Program, Baylor College of Medicine, 3Department of Pediatrics, Baylor College of Medicine, 4Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, 5Department of Molecular and Human Genetics, Baylor College of Medicine, 6Department of Neuroscience, Baylor College of Medicine, 7Howard Hughes Medical Institute, Baylor College of Medicine

JoVE 59542


Recording Mouse Ultrasonic Vocalizations to Evaluate Social Communication

1Human Genetics and Cognitive Functions, University Paris Diderot, CNRS UMR 3571, Institut Pasteur, 2Neurophysiology and Behavior, University Pierre et Marie Curie Paris 6, CNRS UMR 7102, 3Bio Image Analysis, CNRS URA 2582, Institut Pasteur

JoVE 53871


Candidate Gene Testing in Clinical Cohort Studies with Multiplexed Genotyping and Mass Spectrometry

1Molecular Genetics of Chronic Inflammation and Allergic Disease, Max-Delbrück Center for Molecular Medicine, 2Murdoch Childrens Research Institute, 3Department of Paediatrics, University of Melbourne, 4Centre for Social and Early Emotional Development, Faculty of Health, Deakin University, 5Department of Paediatrics, University of Western Australia

JoVE 57601


Generation of Escape Variants of Neutralizing Influenza Virus Monoclonal Antibodies

1Department of Microbiology, Icahn School of Medicine at Mount Sinai, 2Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, 3The Department of Medicine, Section of Rheumatology, The Knapp Center for Lupus and Immunology Research, The University of Chicago

JoVE 56067

 Immunology and Infection
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