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35569_Ward's World+MGH Human Genetics

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Human Genetics Article by: Margaret W. Thompson, Departments of Medical Genetics and Pediatrics, University of Toronto and the Hospital for Sick Children, Toronto, Ontario, Canada. Carter L. Denniston, Department of Medical Genetics, University of Wisconsin, Madison, Wisconsin. Friedrich Vogel, Institute for Anthropology and Human Genetics, Im Neuenheimer Feld, Germany. William L. Nyhan, Department of Pediatrics, University of California, San Diego, California. Access to this content is available to Ward's World readers for free from McGraw Hill's AccessScience, an award-winning, digital STEM resource containing exclusive articles written by expert scientists and engineers; biographies of well-known scientific figures; science news, videos, and animations; and much, much more. Instructors can use AccessScience to guide students on their research project journeys, to help students understand scientific concepts, to support distance learning efforts, in flipped classroom approaches, and in countless other ways. Ward's World and AccessScience have partnered to offer educators a no-obligation, free trial subscription to AccessScience. Request your free trial today to discover how valuable AccessScience can be for you and your students! Get your free trial now. A scientific discipline concerned with genetically deter- mined resemblances and differences among human beings. Human genetics analyzes all aspects of inheritance occurring in humans. Although the mechanism by which heredity operates remained mostly unknown until the twentieth century, the idea that certain physical and mental characteristics, normal or abnormal, can "run in families" goes back to ancient times. Formerly, genetics was thought to be concerned only with the familial transmission of rare and insignificant characteristics, but its fundamental biological role is now apparent. Genes, the units of heredity, have two unique properties: they are self-replicating, and they carry (in their biochemical structure) the codes for protein synthesis (Fig. 1). Consequently, genes play the double role of transmitting genetic information from generation to generation and of governing all the activities of living cells. Expansion of the knowledge of human genetics has come from various directions. For example, technological advances in the visualization of human chromosomes have shown that abnor- malities of chromosome number or structure are surprisingly common and of many different kinds, and that they account for birth defects or mental impairment in many individuals, as well as for numerous early spontaneous abortions. Progress in mo- lecular biology has clarified the molecular structure of chromo- + ward ' s science Content • Chromosome and gene structure • Mutation • Single-gene inheritance • Quantitative inheritance • Hereditary diseases • Chromosomal diseases • Diseases with mendelian inheritance • Multifactorial diseases • Biochemical genetics • Inheritance mechanism • Inborn errors of amino acid metabolism • Mitochondrial disease Key Concepts • Human cells normally contain 23 pairs of chromosomes (46 total), and are considered diploid cells. • Human reproductive cells (eggs and sperm) normally contain 23 total chromo- somes—22 autosomes and one sex chromosome—and are considered haploid. • A very large amount of genetic variation exists in the human population. • Hereditary diseases in humans include chromosomal diseases such as Down syndrome, diseases with mendelian modes of inheritance such as hemophilia, and multifactorial diseases such as diabetes mellitus. • Not all familial traits are hereditary because relatives tend to share common environments as well as common genes. • Biochemical genetics involves the study of the molecular mechanisms of inheritance, inborn errors of amino acid metabolism.

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