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Down Syndrome: A chromosome disorder associated either with an extra chromosome 21 or an effective trisomy for chromosome 21. Clinical manifestations include hypotonia, short stature, brachycephaly, upslanting palpebral fissures, epicanthus, Brushfield spots on the iris, protruding tongue, small ears, short, broad hands, fifth finger clinodactyly, Simian crease, and moderate to severe Intellectual disability. Cardiac and gastrointestinal malformations, a marked increase in the incidence of Leukemia, and the early onset of Alzheimer disease are also associated with this condition. Pathologic features include the development of Neurofibrillary tangles in neurons and the deposition of Amyloid beta-protein, similar to the pathology of Alzheimer disease. (Menkes, Textbook of Child Neurology, 5th ed, p213)

Karyotyping

JoVE 10787

Describing the number and physical features of chromosomes can reveal abnormalities that underlie genetic diseases. This description is facilitated by special staining techniques that produce a particular banding pattern on each chromosome. State-of-the-art techniques make this approach even more powerful, enabling the detection of individual genes that cause disease.

Some genetic diseases can be detected by looking at the structure and number of chromosomes that form when DNA is compacted during mitosis. Once chromosomes are formed, cytogeneticists halt mitosis and perform the staining. The staining produces a distinct banding pattern that reveals different characteristics such as number, shape, and type of chromosomes. Such a description of an individual’s chromosomes is called a karyotype. To facilitate karyotyping, an image is taken of the stained chromosomes, and individual chromosomes are identified and cut out from the image. The chromosomes are then arranged in pairs and ordered by size. This layout is called a karyogram. In a human karyogram, the 22 autosomes are labeled 1 through 22, from the largest to the smallest pair. The two sex chromosomes are labeled X or Y. A karyogram makes it easy to spot missing or additional pieces of a chromosome, or a whole extra copy, all of which can underlie genetic diseases. Marthe Gautier, J&

 Core: DNA Structure and Function

Meiosis I

JoVE 10767

Meiosis is a carefully orchestrated set of cell divisions, the goal of which—in humans—is to produce haploid sperm or eggs, each containing half the number of chromosomes present in somatic cells elsewhere in the body. Meiosis I is the first such division, and involves several key steps, among them: condensation of replicated chromosomes in diploid cells; the pairing of homologous chromosomes and their exchange of information; and finally, the separation of homologous chromosomes by a microtubule-based network. This last step segregates homologs between two haploid precursor cells that may subsequently enter the second phase of meiosis, meiosis II. The exchange of equivalent segments between homologous chromosomes occurs early on during meiosis I, and is referred to as crossing over. This process relies on the close association of such homologs, which are drawn together by the formation of a connective protein framework called the synaptonemal complex between them. To function correctly, the complex requires three parts: (1) vertical lateral elements, which form along the inward-facing sides of two juxtaposed homologous chromosomes; (2) a vertical central element positioned between the chromosomes; and (3) transverse filaments, or horizontal protein threads that connect the vertical and central components. The result has often been compared to a ladde

 Core: Meiosis

Nondisjunction

JoVE 11013

During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes. When an abnormal gamete fuses with a normal gamete, the resulting zygote has an abnormal number of chromosomes and is called aneuploid. An individual with one too few chromosomes has monosomy (45; 2n-1), while trisomy is the presence of one too many chromosomes for a total of 47 (2n+1). Down Syndrome is one well-studied trisomy, where individuals have three copies of chromosome 21. Aneuploid zygotes account for around 70% of spontaneous abortions during gestation. Nondisjunction is more common in sex chromosomes than autosomes. Individuals can have a variety of sex chromosome combinations, including one or more additional sex chromosomes (e.g., XXY, XXX, XYY) or the presence of only a single sex chromosome (denoted X0). These individuals tend to have normal lifespans, though with sometimes major physiological and reproductive consequences. Nondisjunction appears to be more

 Core: Meiosis

Oogenesis

JoVE 10906

In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from the equivalent procedure of spermatogenesis in males. First, meiotic divisions during oogenesis are asymmetric, meaning that a large oocyte (containing most of the cytoplasm) and minor polar body are produced as a result of meiosis I, and again following meiosis II. Since only oocytes will go on to form embryos if fertilized, this unequal distribution of cell contents ensures that there are enough cytoplasm and nutrients to nourish the early stages of development. Second, during oogenesis, meiosis “arrests” at two distinct points: once during embryonic growth and a second time during puberty. In mammals, oocytes are suspended in prophase I until sexual maturation, at which point meiosis I continues under hormonal influence until an egg precursor cell is released into a fallopian tube. At ovulation, the precursor exits the ovary and, only if fertilization occurs, is stimulated to complete meiosis II and form a complete egg. Defects during oogenesis can result in severe consequences. In particular, problems with chromosome segregation during either meiosis I or meiosis II may lead to an embryo being aneuploid, meaning that it contains an abnormal number of chromosomes. Increased age elevates a woman

 Core: Reproduction and Development

Cytogenetics

JoVE 5545

Cytogenetics is the field of study devoted to chromosomes, and involves the direct observation of a cell’s chromosomal number and structure, together known as its karyotype. Many chromosomal abnormalities are associated with disease. Each chromosome in a karyotype can be stained with a variety of dyes to give unique banding patterns. More recent techniques, including …

 Genetics

Detection of Copy Number Alterations Using Single Cell Sequencing

1Koch Institute for Integrative Cancer Research, Department of Biology, Massachusetts Institute of Technology, 2Howard Hughes Medical Institute, 3Division of Health Sciences and Technology, Harvard Medical School, 4The Barbara K. Ostrom (1978) Bioinformatics and Computing Facility in the Swanson Biotechnology Center, Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, 5BioMicro Center, Department of Biology, Massachusetts Institute of Technology

JoVE 55143

 Genetics

Ultrasound Images of the Tongue: A Tutorial for Assessment and Remediation of Speech Sound Errors

1Department of Communication Sciences and Disorders, Syracuse University, 2Haskins Laboratories, 3Department of Communicative Sciences and Disorders, New York University, 4Department of Communication Sciences and Disorders, University of Cincinnati, 5Program in Speech-Language-Hearing Sciences, City University of New York Graduate Center, 6Department of Linguistics, Yale University

JoVE 55123

 Behavior

The Production of Pluripotent Stem Cells from Mouse Amniotic Fluid Cells Using a Transposon System

1Stem Cell and Regenerative Medicine Laboratory, Fondazione Istituto di Ricerca Pediatrica Citta della Speranza, 2Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, 3Stem Cells and Regenerative Medicine Section, Developmental Biology and Cancer Programme, UCL Institute of Child Health and Great Ormond Street Hospital

JoVE 54598

 Developmental Biology

A High Throughput, Multiplexed and Targeted Proteomic CSF Assay to Quantify Neurodegenerative Biomarkers and Apolipoprotein E Isoforms Status

1Centre for Translational Omics, Genetics and Genomic Medicine Deptartment, Great Ormond Street Institute of Child Health, University College London, 2Dementia Research Centre, Institute of Neurology, University College London, 3Clinical Neurochemistry Laboratory, Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy, University of Gothenburg, 4Neurology Unit, Department of Pathophysiology and Transplantation, University of Milan, 5Great Ormond Street Hospital for Children, University College London

JoVE 54541

 Medicine

Dissection of Hippocampal Dentate Gyrus from Adult Mouse

1Japan Science and Technology Agency, Core Research for Evolutionary Science and Technology (CREST), 2Division of Systems Medical Science, Institute for Comprehensive Medical Science, Fujita Health University, 3Department of Psychiatry, Graduate School of Medicine, Kyoto University, 4Genetic Engineering and Functional Genomics Group, Horizontal Medical Research Organization, Graduate School of Medicine, Kyoto University, 5Center for Genetic Analysis of Behavior, National Institute for Physiological Sciences, National Institutes of Natural Sciences

JoVE 1543

 Biology
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