Meiosis Study Guide Answers What is the Purpose of Meiosis

**Meiosis Study Guide** **Name** Answer Key **Date** **Per** 1. What is the purpose of meiosis? The purpose of meiosis is to produce gametes with a haploid number of chromosomes that all differ from one another.   2. Name 2 types of cells that are haploid. sperm and egg 3. Fill in the blanks with the best word or phrase using the word bank to the right. (All words may not be used.) During Interphase before Meiosis, the DNA is replicated. During Prophase I, homologous chromosomes pair up as tetrads and undergo the process called   synapsis. During this process, segments of chromosomes from mom are exchanged with similar segments of chromosomes from dad. This process of synapsis and crossing over leads to genetic   recombination in the offspring. During Metaphase I, the homologous pairs orient themselves along the metaphase plate (middle of the cell)   next to each other. This random orientation of homologues is another major reason for genetic variation in offspring. With 23 pairs of chromosomes, the human cells have 2 to the power of 23 or   8,388,608 ways to orient themselves along the metaphase plate. During Anaphase I, the homologous chromosomes separate and each one is pulled   by spindle fibers to the opposite poles of the cell. During Telophase I, the nuclear membrane forms around the separated chromosomes and the cell will have 2 daughter cells with a haploid number of 23 chromosomes each. Cytokinesis will pinch the cytoplasm in the middle, leading to 2 daughter cells with a haploid number of 23 chromosomes each. During Meiosis II, the spindle fibers will attach to the centromere of each chromosome to line them up in the middle of the cell. During Anaphase II, the spindle fibers will shorten and pull apart the sister chromatids   of each duplicated chromosome to opposite poles of the cell. By the end of Meiosis II, there will be 4 daughter cells which are genetically   different from each other. Diagram a pair of homologous chromosomes undergoing synapsis and then crossing over. Explain what is occurring with the chromosomes.   **Word Bank** Synapsis Crossing over Recombination Homologous chromosomes Spindle fibers Sister chromatid Replicated Homologous Next Nuclear membrane Haploid Diploid **Mitosis** begins with a single **diploid (2n)** cell and results in **2 identical** cells. **Meiosis I** begins with a single **diploid (2n)** cell and results in **4 different** cells. Meiosis II is technically a **mitotic-style equational** division during which the sister chromatids in the two haploid cells **separate**. Meiosis results in a total of **4 haploid** cells. **Are all the gametes (egg or sperm cells) produced by one individual the same? Explain, giving 2 reasons based on Meiosis.** No, because of **crossing over during prophase I** and **independent assortment during metaphase   I**, all the cells are different. **What occurs during fertilization?** The sperm fuses with the egg and releases its 23 chromosomes into the ovum creating a diploid zygote.   **Is the resulting zygote/embryo haploid or diploid? Explain.** Diploid. A zygote is formed by the fusion of two haploid gametes (sperm and egg), resulting in a diploid cell with a full set of chromosomes. **For each of the following statements about Meiosis (and the Cell Cycle for Meiosis) determine the specific phase in which the events described in each statement occur.**   1. Sister chromatids move to opposite poles of the cell. **Anaphase II** 2. Homologous chromosomes align in the center of the cell. **Metaphase I** 3. DNA replication occurs. **Interphase** 4. Tetrads are formed. **Prophase I** 5. Homologous chromosomes move to opposite poles of the cell. **Anaphase I** 6. Four daughter cells are formed. **Cytokinesis (after Meiosis II)** 7. Crossing over occurs. **Prophase I** 8. Two daughter cells are formed. **Cytokinesis (after Meiosis I)** **Use the following chart to describe the differences between mitosis and meiosis.** | Characteristic | Mitosis | Meiosis | |---|---|---| | Goal or function | make two identical cells | make 4 different haploid cells | | Creates what sort of cells? | Somatic | Sex | | Creates genetically-identical or different cells? | identical | different | | Number of divisions | 1 | 2 | | No. of daughter cells; diploid 2n or haploid n? | 2 diploid | 4 haploid | | Pairing of homologous chromosomes (Yes/No) | No | Yes | | Crossing over (Yes/No) | No | Yes |