II. Read the following text paying attention to the highlighted words. Explain or interpret the contextual meaning of the underlined phrases

Since prehistoric times, man has recognized the influence of heredity and has applied its principles to the improvement of cultivated crops and domestic animals. Most of the mechanisms of heredity, however, remained a mystery until the 20th century, when scientifically supported information became available.

Genetics may be defined as the study of the way in which genes operate and the way in which they are transmitted from parents to offspring. Modern genetics involves study of the mechanism of gene action — the way in which the genetic material affects physiological reactions within the cell. Although genes determine the features an individual may develop, the features that actually develop depend upon the complex interaction between genes and their environment. Genetics overlaps many different branches of biology such as biochemistry, cytology, microbiology, etc., and many other sciences; e.g., chemistry, physics, mathematics, sociology, psychology, and medicine.

Classical genetics, which remains a basis for all other topics in genetics, is concerned primarily with the method by which genetic traits classified as dominant (always expressed), recessive (subordinate to a dominant trait), intermediate (partially expressed), or polygenic (due to multiple genes) are transmitted in plants and animals. These traits may be sex-linked (result from the action of a gene on the sex, or X, chromosome) or autosomal (result from the action of a gene on a chromosome other than a sex chromosome). Classical genetics began with Mendel's study of inheritance in garden peas and continues with studies of inheritance in many different plants and animals.

Cytogenetics blends the skills of cytologists, who study the structure and activities of cells, with those of geneticists, who study the relationship between the mechanism of heredity and cellular activities. Cytologists discovered chromosomes and the way in which they duplicate and separate during cell division at about the same time that geneticists began to understand the behaviour of genes at the cellular level. The close correlation between the two disciplines led to their combination. Molecular genetics includes the study of the molecular nature of the gene and the method by which genes control the activities of the cell.

A study of genes in populations of animals, population genetics, provides information on past migrations, evolutionary relationships and extents of mixing among different varieties and species, and methods of adaptation to the environment. Statistical methods are used to analyze gene distributions and chromosomal variations in populations.

Some geneticists specialize in human genetics. When classical geneticists first determined the principles of heredity in plants, fruit flies, mice, and other forms of life, they tried to interpret man's heredity in a similar way but found many traits that did not fit the patterns. As techniques improved, it was found that the method of inheritance of human characteristics is the same as that for other living things.

Geneticists use a wide range of methods and techniques in their research work. When animals that differ with respect to one or more primary traits are bred, and their offspring then are bred among themselves to give a second generation, the method of inheritance of the trait can be determined; the process is known as experimental breeding. Cytogenetic techniques are closely associated with experimental breeding. Biochemical techniques are used to determine the activities of genes within cells. Chemical tests are used to distinguish certain inherited characteristics of man; e.g., urinalysis and blood analysis reveal the presence of certain inherited abnormalities—phenylketonuria (PKU), cystinuria, alkaptonuria, gout, and galactosemia. Mathematical techniques are used extensively in genetics. The laws of probability are applicable to crossbreeding and are used to predict ratios concerning the appearance of specific traits in offspring.

Nowadays genetic techniques are used nearly in all spheres of human activities. Agriculture and animal husbandry apply genetic techniques to improve plants and animals. Plant geneticists produce new species by special treatment; e.g., a hybrid grain has been produced from wheat and rye, and plants resistant to destruction by insect pests have been developed. Plant breeders use the techniques of budding and grafting to maintain desirable gene combinations originally obtained from crossbreeding. The use of the chemical compound colchicine, which causes chromosomes to double in number, has resulted in many new varieties of fruits, vegetables, and flowers. Animal breeders use artificial insemination to propagate the genes of prize bulls. Prize cows can transmit their genes to hundreds of offspring by hormone treatment, which stimulates the release of many eggs that are collected, fertilized, and transplanted to foster mothers.

Various industries employ geneticists; the brewing industry, for example, may use geneticists to obtain strains of yeast that produce large quantities of alcohol. The pharmaceutical industry has developed strains of molds, bacteria, and other microorganisms high in antibiotic yield.

Genetic techniques are used in medicine to diagnose and treat inherited human disorders. Knowledge of a family history of cancer or tuberculosis may indicate a hereditary tendency to develop these afflictions. Cells from embryonic membranes reveal certain genetic abnormalities, including enzyme deficiencies, that may be present in newborn babies, and thus permit early treatment. Many countries require a blood test of newborn babies to determine the presence of an enzyme necessary to convert an amino acid, phenylalanine, into simpler products. Phenylketonuria, which results from lack of the enzyme, causes permanent brain damage if not treated soon after birth. The presence of approximately 100 different types of human genetic diseases can be detected in embryos as young as 12 weeks; the procedure, called amniocentesis, involves removal and testing of a small amount of fluid from around the embryo.

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I. Match each word on the left to its correct definition on the right	\|	Vocabulary notes

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