Meiosis: four different daughter cells
In meiosis, the nucleus divides twice. This produces four haploid nuclei. The number of chromosomes is therefore halved during meiosis. Moreover, homologous chromosomes within a pair can exchange genetic material before being separated. The daughter cells are therefore genetically different from the parent cell (and from each other).
Meiosis is the basis of sexual reproduction, occurring at some point in the life cycle of organisms that reproduce sexually. The haploid gametes produced by meiosis fuse during fertilization. This means that the new fertilized cell has the diploid number of chromosomes. Without meiosis in the life cycle, the number of chromosomes of a sexually reproducing species would be doubled in each generation.
■ Glossary of essential terms for you to know
| № | English term | Russian equivalent |
| essential | необходимый | |
| reproduction | воспроизведение, размножение | |
| generation | поколение | |
| affinity | сходство, родство | |
| dye | краска | |
| to cut out | вытеснять, отбрасывать | |
| mutation | мутация | |
| to double | удваивать | |
| asexual | бесполый | |
| multicellular | многоклеточный | |
| to carry out | выполнять | |
| to replicate | дублировать | |
| division | деление | |
| to attach | прикреплять | |
| strand | нить | |
| according to | согласно | |
| to fuse | сплавляться, сливаться | |
| fertilization | оплодотворение, удобрение | |
| to damage | повреждать | |
| nucleus | ядро | |
| mitosis | митоз, непрямое деление ядра | |
| meiosis | мейоз, редукционное деление | |
| to provide | обеспечивать | |
| continuity | непрерывность, неразрывность | |
| stain | краситель, пятно | |
| to wrap | обертывать | |
| apart from | кроме, помимо | |
| gene | ген | |
| species | вид | |
| gamete | половая клетка | |
| give rise to | давать начало | |
| sequence | последовательность | |
| to occur | происходить | |
| duration | длительность | |
| to vary | различаться |
■ Your Essential Assignments
I. Quick check:
1. a) List the main stages of mitosis, starting with interphase.
b) At which stage is DNA replicated?
2. Compare mitosis and meiosis in terms of number of cell divisions and number of daughter cells.
II. Fill in the missing words:
| Term (verb) | Noun | Adjective |
| replace | ....... | ....... |
| continue | ....... | ....... |
| condition | ....... | ....... |
| fuse | ....... | ....... |
| mutate | ....... | ....... |
| double | ….. | …… |
III. Use monolingual English dictionary and write down what could the words given below mean:
affinity, give rise to, division, asexual, generation.
IV. Match these words with their definitions:
| 1. | cell | A. | not having sexual organs or having sex |
| 2. | multicellular | B. | to make sperm join an egg so that a young baby or animal develops |
| 3. | reproduction | C. | a change in the genetic structure of an animal or plant, that makes it different from others of the same type |
| 4. | gamete | D. | the sequence of events that occurs between one cell division and the next cycle |
| 5. | fertilization | E. | the central part of an atom, made up of neutrons, protons, and other elementary particles |
| 6. | chromosome | F. | a group of animals or plants which are all similar and can breed together to produce young animals or plants of the same kind as them |
| 7. | nucleus | G. | to become twice |
| 8. | asexual | H. | the act or process of producing young animals or plants |
| 9. | mutation | I. | a part of every living cell that is shaped like a thread which controls the character, shape etc. that a plant or animal has |
| 10. | species | J. | a type of cell which joins with another cell, starting the development of a baby or other young creature |
| 11. | to double | K. | more than one cell |
| 12. | cell cycle | L. | the smallest part of a living thing that can exist independently |
V. Find English equivalents to the following word combinations:
| № | Russian term | English equivalent |
| 1. | деление клеток | |
| 2. | многоклеточный организм | |
| 3. | поврежденные клетки | |
| 4. | основа размножения | |
| 5. | генетический материал | |
| 6. | согласно их размеру | |
| 7. | дочерняя клетка | |
| 8. | родительская клетка | |
| 9. | бесполое размножение | |
| 10. | выполняет свои функции | |
| 11. | становится видимым | |
| 12. | длительность клеточного цикла | |
| 13. | во время оплодотворения | |
| 14. | жизненный цикл организмов |
VI. Give Russian equivalents to the following English terms:
| № | English term | Russian equivalent |
| to consist of DNA | ||
| wrapped in protein | ||
| matching pairs | ||
| two sets of chromosomes | ||
| identical nuclei | ||
| to be identical to sth. | ||
| without changing the genetic information | ||
| for growth of a multicellular organism | ||
| nuclear division | ||
| human nerve cells | ||
| sexual reproduction | ||
| fertilized cell | ||
| the light microscope | ||
| to contain the same genes | ||
| can exchange genetic material | ||
| genetically different from |
VII. Find synonyms among the pool of words: