Meiosis

**Meiosis**



**Activity One** You have already discovered that biology has its own language. Your cell division unit offers a whole new set of vocabulary words that you will need to learn. First try your hand at determining the meanings of the words below by checking out this list of prefixes and suffixes (you will not find **all** the words this way). Check your work by consulting your textbook or this [|biology resource page], which contains a variety of online resources. Please do not use a dictionary, online or otherwise, because the terms are taken out of context and may be misleading.

**Activity Two**
 * **gamete** || **homozygous** || **haploid** || **genotype** ||
 * **zygote** || **heterozygous.....................** || **crossing over.......................** || **phenotype** ||
 * **fertilization.................** || **homologous** || **tetrad** || **chiasma** ||
 * **synapse** || **diploid** || **centromere** || **cytokinesis** ||
 * **variation** || **chromosome** || **chromatin** || **chromatid** ||
 * Meiosis, like mitosis, is a process of cell division. However, unlike mitosis, meiosis involves two parents who contribute different genetic material to the process. Recall that mitosis is a cloning process: the daughter cells are identical to the parent cell. Meiosis, on the other hand, creates daughter cells that are uniquely different, not only from their parent cells, but from each other.**

The two cells involved in meiosis are **sperm** and **egg** cells. These begin as [|diploid cells] in either the testes or the ovaries. Each parent cell (whether sperm or egg) is a composite of its parent cells' DNA: half its DNA came from the male parent and half from the female parent. This combination of the parents' DNA is the basis of the sex cells' uniqueness.

In [|Meiosis I], the DNA is replicated and the parent cell divides, creating two daughter cells, each of which still has the diploid number of chromosomes. In [|Meiosis II], the DNA DOES NOT replicate again, but the two daughter cells divide once more to create a total of four haploid daughter cells.
 * This [|animated tutorial] will walk you through the steps of meiosis.**

**Activity Three**
 * When does crossing over take place?
 * What is the result of crossing over?
 * Why must the daughter cells in meiosis be haploid rather than diploid like the parent cell?
 * Work through [|this tutorial] and follow the links to view the animations. You will need [|this link] to answer the questions on your worksheet.**

**Activity Four**  View the Unitedstreaming video on Meiosis. Answer the following questions: 1. When does crossing over take place? What is the chiasma? 2. How does crossing over take place? Can crossing over take place more than once per chromosome? 3. Explain the terms haploid and diploid in terms of human meiosis. 4. Where does meiosis take place in males? (spermatogenesis) 5. Where does meiosis take place in females? (oogenesis) 6. Describe how female meiosis differs from that of males in terms of daughter cells (gametes). 7. What process allows the formation of a diploid zygote. 8. What is the number of gene combination possibilities in humans? 9. What is a tetrad? 10. What causes nondisjunction? What is the result of nondisjunction? How does this affect the cell? 11. What is the most common chromosomal abnormality that results in live birth? 12. What is Turner's Syndrome? 13. What is Klinefelter's Syndrome? 14. What is the most common risk factor for nondisjunction? 15. What is polyploidy? 16. Why is polyploidy good in plants but not in animals? 17. How does crossing over encourage variation among populations? 18. How does this tie in with "survival of the fittest?" 19. What is a mutation? 20. How are mutations passed on to offspring? 21. What is the difference between natural selection and selective breeding?

**Activity Five** **Before embarking on the activity below, read about the [|differences between mitosis and meiosis.]**
 * **How does nature overcome the limitations of asexual reproduction?**

 Your teacher will distribute materials for your //**Comparing Mitosis and Meiosis**// activity:
 * Large sheet of white paper
 * Markers
 * Pencils
 * "cell" template
 * Chromosomes - (tubing)
 * genes (colored stickers)
 * scissors
 * velcro circles

1. Follow the procedure on your lab sheet to put together your genes and chromosomes. 2. Use a template to draw your cells. 3. Work with your partner to develop a script or narrative that describes each step is the processes of mitosis and meiosis. **You must know your script by heart** so that you can narrate while you manipulate the "chromosomes" through the process. __The script must include all the terms in Activity One above (except fertilization, zygote, genotype and phenotype) as well as others listed on your lab sheet.__ You must correctly use the vocabulary that you learned. 4. While writing the script is a joint effort between partners, the rest of the activity is not. Each partner will be expected to move the chromosomes while describing which stage the chromosomes are in and the important events of each stage. 5. After you have received a grade for your activity, complete the analysis and conclusions on the back of the lab sheet.

**Do your very best on this activity; it is the equivalent of a test grade for this unit.**

