X. Give the key words (phrases) to the text. Give the summary.
XI. Translate without a dictionary. Guess the meaning of unknown words from the context. Give the main idea of each paragraph:
a) In general, genes are very stable. They replicate exactly and remain unchanged from one generation to another. They are capable of undergoing change, however, and these changes may result in modification of the gene's action. The geneticist recognizes this change in action in the phenotype. Once a mutation has taken place, the altered form of the gene is copied exactly, and if the change occurred in a germ cell or in a cell which will finally give rise to germ cells, it may be inherited and become a part of the genetic make-up of the population. The frequency with which mutations appear depends to some extent on environmental conditions. The study of mutations and how they arise can lead to a clearer understanding of what genes are and how they function. For these reasons it was indeed a great step forward when mutations in Drosophila were discovered.
b) With a good microscope, we can see that in the nucleus of every cell there are tiny particles that look like dots. These dots are made of a material called chromatin. The chromatin particles form threads. These are the threads that are usually to be found coiled and twisted inside the nucleus. These threads of chromatin are called chromosomes and they contain genes.
There must be something in the chromatin that decides what the offspring is going to look like. You know, of course, that a person has many different traits or features. Whatever controls these traits must be packed into the microscopic nucleus. Scientists believe that there are tiny structures in the chromatin that control all the different traits. These structures, which are so small that they cannot be seen even under the microscope, are called genes.
Genes are extremely important. You have genes for all your body organs: for hair, skin and eye colour; for blood type and for intelligence. In fact, genes are responsible for almost all the features that make you look different from anybody else. A single gene may even change your whole life. In the nucleus of every cell of your body there are about 20 000 genes all together, these genes do much to decide what you look like.
c) Scientists thought it would be interesting to make account of these chromosomes in the cell. It was found soon that each particular kind of animal or plant has its own definite number of chromosomes. Even the shape of each chromosome remains the same in all the cells. And when the cell divides, each chromosome divides lengthwise also. It divides in a manner that every gene in that chromosome also splits in two. In this manner, every cell in the body has the same number of chromosomes and the same gene.
Read and translate the following words:
variety, desirable, characteristics, nevertheless, possess, process, yield, quality, improvement, heredity, genetics, technique, require, important, discard, example, resistant, survive, severe, improve, superior, strain, procedure, row, refer to, progeny, parent, appearance, comparison.
Date: 2016-01-03; view: 1106