Kami Export - 208014 King - 17 Meiosis-S.pdf - Meiosis How does sexual reproduction lead to genetic variation Why Cells reproduce through mitosis to

Kami Export - 208014 King - 17 Meiosis-S.pdf - Meiosis How...

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Unformatted text preview: Meiosis How does sexual reproduction lead to genetic variation? Why? Cells reproduce through mitosis to make exact copies of the original cell. This is done for growth and repair. Sexually-reproducing organisms have a second form of cell division that produces reproductive cells with half the number of chromosomes. This process is called meiosis, and without it, humans, oak trees, beetles, and all other sexually-reproducing organisms would be vastly different than they are today. Model 1 – Meiosis I Sister chromatids Cell from the sex organs (ovaries/testes in animals) during Interphase I Homologous chromosomes come together to form a tetrad Single chromosome Early Prophase I Late Prophase I Telophase I Metaphase I Anaphase I   1. According to Model 1, in what type of organs are the cells that enter meiosis I found? The type of organs that cells enter during meiosis I are the sex organs.   2. Considering what you already know about mitosis in cells, what event must take place during interphase before a cell proceeds to division? The DNA needs to replicate, or the S phase, in order for it to proceed to division. Meiosis 1 3. What two structures make up a single replicated chromosome? Sister chromatids. 4. In Model 1, how many replicated chromosomes does the cell contain during prophase? There are four replicated chromosomes during prophase. Read This! Alleles are alternative forms of the same gene. For example, gene A may contain the information for fur color. One allele “A” may result in white fur, while the alternative allele “a” may result in black fur. Homologous chromosomes are chromosomes that contain the same genes, although each chromosome in the homologous pair may have different alleles. 5. At which stage in meiosis I do the pairs of homologous chromosomes come together? Late Prophase 6. Once the chromosomes have formed a pair, what are they called? They are called a tetrad. 7. At the end of meiosis I, two cells have been produced. How many replicated chromosomes are in each of these cells? There are two sets of replicated chromosomes in each of the cells. 8. Cells with a full set of chromosomes are referred to as diploid or 2n, whereas cells with half the chromosomes are haploid or n. At which stage(s) of meiosis I are the cells diploid and at which stage(s) are they haploid? The diploid: Metaphase, early prophase, late prophase, anaphase. The haploid: Telophase 9. Which of the statements below correctly describes the relationship between the cells at the end of telophase I and the original cell? a. The new cells have one copy of all of the genetic information in the original cell. b. The new cells have two copies of all of the genetic information in the original cell. c. The new cells have one copy of half of the genetic information in the original cell. d. The new cells have two copies of half of the genetic information in the original cell. 10. Considering the genetic makeup of the homologous pairs, will the cells at the end of telophase I be genetically identical to each other? No, the homologous pairs will be separated, and the alleles may not be identical. 2 POGIL™ Activities for High School Biology Model 2 – Meiosis II Two cells from Meiosis I in Prophase II Metaphase II Anaphase II Telophase II 11. According to Model 2, where did each of the cells come from that started meiosis II? Each of the two cells came from Meiosis I. 12. In meiosis I, during anaphase I, which structures separated—homologous chromosomes or sister chromatids? The homologous chromosomes. 13. In meiosis II, during anaphase II, which structures separated—homologous chromosomes or sister chromatids? The sister chromatids. 14. At the end of the meiosis II are four daughter cells. Are they haploid or diploid? Explain your answer in a complete sentence. They are haploid, because they have half of what the beginning cell started out with. 15. Which of the statements below correctly describes the relationship between the cells at the end of meiosis II and the original cell? a. The new cells have one copy of all of the genetic information in the original cell. b. The new cells have two copies of all of the genetic information in the original cell. c. The new cells have one copy of half of the genetic information in the original cell. study d. The new cells have two copies of half of the genetic information in the original cell. Meiosis 3 Model 3 – Gametogenesis and Fertilization (Human) Males Females Secondary oocyte (end of meiosis I) Secondary spermatocyte (end of meiosis I) Fertilization Spermatids (end of meiosis II) Mature sperm Oocyte proceeds to meiosis II Polar body eventually degenerates Zygote with half its chromosmes from the female (maternal) and half from the male (paternal) 16. According to Model 3, what is the name given to the cells produced at the end of meiosis I in males? Secondary spermatocyte. 17. What is the name given to the cells produced at the end of meiosis I in females? Secondary oocyte. 18. Refer to Model 3. a. At the end of meiosis II in males, what cells are produced? Spermatids b. What do these cells (from the previous question) eventually become? They eventually become mature sperm. 19. Before fertilization, what happens to the secondary oocyte? What happens to the secondary oocyte is it goes through meiosis II. 20. During fertilization which two cells come together? Be specific in your answer. The mature sperm and the secondary oocyte come together (sperm and the egg.) 4 POGIL™ Activities for High School Biology 21. During meiosis II, the secondary oocyte divides unevenly, with one cell (the ovum) receiving half of the chromosomes and nearly all the cytoplasm and organelles, while the other cell, the polar body, is much smaller and eventually degenerates. With your group, propose an explanation to explain why the secondary oocyte divides in this way. Because it needed a way to become haploid, and it didn't really need anything else afterwards; the ovum needs the nutrients in order to produce a baby with the mature sperm. (Fertilize) 22. What is the ploidy of the zygote produced by fertilization—haploid or diploid? They are diploid. 23. What would the ploidy of the zygote be if egg and sperm were produced by mitosis rather than meiosis? How would this affect the ploidy of each successive generation? The ploidy of the egg and sperm would be diploid, the zygote would be tetraploid, and two tetraploid zygotes would become octoploid, and each successive generation would double. 24. With your group write a statement to explain the origin of the chromosomes found in the zygote. Your statement must include the term homologous pair. The homologous pairs came from each parent; half is maternal, and half is paternal. Meiosis 5 Extension Questions Model 4 – Crossover of DNA in Chromosomes Chiasma Homologous pair of chromosomes (tetrad) during Prophase I Recombinant chromatids 25. At which stage of meiosis are the chromosomes in Model 4? They are in prophase I. 26. When the chromosomes come together as homologous pairs, the arms of the sister chromatids may cross over. a. What are these crossover points called? Chiasma b. Describe what happens to the chromatids during crossover. The chromatids switch from one sister chromatid to another 27. What phrase is used to describe the chromatids after crossing over takes place and the homologous chromosomes separate? Recombinant chromatids. 28. Compare the recombinant chromatids with the original pair. a. Are the genes on a recombinant chromatid the same as the original chromatid? No, because they switched chromatids with one another. b. Are the alleles on a recombinant chromatid the same as the original chromatid? No, because one is paternal and one is maternal. 6 POGIL™ Activities for High School Biology Model 5 – Genetic Variation OR OR Early Prophase I OR Late Prophase I Late Telophase I 29. Model 5 is a condensed version of meiosis I. Notice the two possible arrangements of chromosomes in late prophase I. Considering what you know about DNA replication and meiosis, is either arrangement equally likely during the formation of tetrads in late prophase I? Explain. There is no other arrangement possible, except maybe switching the dark and the gray side on the top. 30. If there were three sets of homologous chromosomes in the cell in Model 5, how many possible arrangements would there be for the tetrads in late prophase I? There are 6 possible arrangements for the tetrads in late prophase I. Read This! When homologous chromosome pairs align on the spindle during metaphase I the orientation of one pair is independent of the orientation of any other pair. This is known as independent assortment. Humans have 46 chromosomes, arranged as 23 pairs. During metaphase I each pair lines up independently, which results in 223 possible combinations. 31. With your group, calculate the number of possible genetic combinations due to independent assortment. There are 23 possible genetic combinations. Meiosis 7 32. As a group, choose one set of daughter cells in late telophase I from Model 5. Imagine that those cells now undergo meiosis II. Draw at least four resulting haploid cells that could result. On paper 33. Meiosis and sexual reproduction each lead to variation in the genetic make-up of every person. With your group, explain how meiotic events, as well as the random fertilization of eggs and sperm, together lead to this genetic variation. chromosomes go through then meiosis leadingII,toleading the genetic differentiation; to 8 million of them TheThe chromosomes in each cell go meiosis through I,meiosis I, then II, meiosis to genetic variations;up upwards of 8 million different 8 POGIL™ Activities for High School Biology ...
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