tailieunhanh - A Dictionary of Genetics phần 4

Tham khảo tài liệu 'a dictionary of genetics phần 4', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 166 fragile X syndrome the males in this F2 generation are retarded. See Appendix C 1969 Lubs 1991 Verkerk et al. CpG island DNA methylation fragile chromosome site parental imprinting trinucleotide repeats. fragile X syndrome See fragile X-associated mental retardation. frameshift mutation See reading frame shift. framework region the highly conserved relatively invariant portion of the variable V region of an immunoglobulin chain as distinguished from the hypervariable segments of the V region. fraternal twins See twins. free energy that component of the total energy of a system that can do work. See thermodynamics second law of. freemartin a mammalian intersex arising due to the masculinization of a female twin by hormones from its male sibling when the fetal circulations are continuous. free radical an unstable and highly reactive molecule bearing an atom with an unpaired electron that nonspecifically attacks a variety of organic structures including DNA. The interaction of ionizing radiation with water can generate hydroxyl and hy-droperoxyl groups free radicals that are potent oxidizing agents . See superoxide anion. free radical theory of aging aging due to the production of reactive free radicals of oxygen that inflict molecular damage to cell organelles especially DNA. These lesions accumulate with time and cause a progressive reduction in viability. See antioxidant enzymes. freeze-drying a method of dehydrating a cell or solution by rapidly freezing its moisture content to ice. The solid material is then dried in the frozen state under vacuum so that ice sublimes directly to water vapor with a minimization of shrinkage. See lyophilize. freeze-etching a technique for preparing biological material for electron microscopy. Live or fixed specimens are frozen in a liquid gas such as freon or nitrogen and then placed in a Balzer freeze-fracture apparatus. This is an instrument that allows frozen tissues to be sectioned in a vacuum. The exposed surface is .