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Discuss these questions with your partner. Then scan the text quickly to find the answers.
1. What is variation?
2. What is mutation?
3. Are mutations harmful or beneficial?
4. How do X-rays influence the mutation rate?
Exercise A. Match the words with their definitions:
| 1. | ultimate | A | being the only one of its kind |
| 2. | unique | B | a process by which two or more things have an effect on each other and work together |
| 3. | distinguish | C | the final and the most important one |
| 4. | source | D | the air, water and land in which people, animals and plants live |
| 5. | feature | E | someone`s child or children; animal`s baby or babies |
| 6. | spontaneous | F | how tall someone is |
| 7. | twin | G | a thing, place, activity that you get something from |
| 8. | offspring | H | a part of something that you notice because it seems important, interesting, or typical |
| 9. | identical | I | to be able to recognize and understand the difference between two similar things or people |
| 10. | environment | J | happening or done without being planned or organized |
| 11. | interaction | K | one of two children born at the same to the same mother |
| 12. | height | L | exactly the same |
■ Read and translate the given text and make your essential assignments:
The Earth is inhabited by billions of organisms, every one of which is unique. Individuals belonging to different species are usually easy to distinguish; members of the same species may differ only in small ways; but even clones (such as identical twins) show some subtle differences. The differences between individuals of the same species are called variation.These differences may be the result of genetic differences, the influence of the environment, or a combination of genetic and environmental influences.
Genetic variation
Genetic differences reflect the genotypeof an organism, that is, its genetic make-up. A diploid organism has two sets of chromosomes and two forms ( alleles)of each particular gene. These alleles may be the same (the organism is homozygous for that gene) or different (the organism is heterozygousfor that gene). If different, one of the alleles (the dominant allele ) may mask the other allele (the recessive allele).The dominant allele is therefore expressed in either the heterozygous or the homozygous condition, whereas the recessive allele is expressed only in the homozygous condition. If an organism is haploid (that is, it has only one set of chromosomes), all its alleles will be expressed and will be reflected in its observable or measurable characters(the features or traits transmitted from parent to offspring).
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