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القسم قسم علوم الحياة
المرحلة 4
أستاذ المادة قاسم محمد علي العامري
4/27/2011 11:36:23 AM
Genetics (The Science of Heredity)
Genes, Chromosomes, and the Genome
Genetics is the science of heredity; it deals with the structure and function of the genes. The cells of all living things contain a program that guides their functioning. This program is genetically determined, i.e., it is transmitted to both newly formed cells during every cell division. The transmission must be precise, since otherwise it leads to disturbances in function (mutations, see below). The genetic program consists of individual information units, the genes (= hereditary characters), with each gene determining a specific function. The sum total of all genes is the genome (the human inheritance includes within a single set of chromosomes approximately 30000?40000 genes; see Chapter 1: The Cell Nucleus), which is contained in the sum of chromosomes in each cell nucleus. Genes are arranged along the chromosomes in a linear fashion and have a definite location and structure. They represent the smallest functional genetic unit; each comprises on an average 1000?10000 base pairs (300?3000 base triplets), a comparatively short chromosome segment (a single set of chromosomes, that is, 23 chromosomes, contains a double strand of DNA with a total length of around 3 billion base pairs). A single gene might, for instance, contain the information for one protein (i.e., how many amino acids it contains and how they are arranged). A single character, on the other hand, may be determined by several genes.
The Allele
With the exception of the sex cells, human cells contain 46 chromosomes: 23 maternal and 23 paternal. In thisway, every gene is present on the corresponding paired homologous chromosome in identical or slightly modified form. The genes that are localized at the same site on both the maternal and paternal chromosomes are called alleles. If both alleles are completely identical in their genetic information, the carrier of such a character is called homozygous; if they differ, the carrier for that character is heterozygous.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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