9. Mitosis and Meiosis

Mitosis

9. Mitosis and Meiosis

Mitosis

4:26 minutes

Problem 32h

Textbook Question

From a piece of blank paper, cut out three sets of four cigar-shaped structures (a total of 12 structures). These will represent chromatids. Be sure each member of a set of four chromatids has the same length and girth. In set one, label two chromatids 'A' and two chromatids 'a.' Cut each of these chromatids about halfway across near their midpoint and slide the two 'A' chromatids together at the cuts to form a single set of attached sister chromatids. Do the same for the 'a' chromatids. In the second set of four chromatids, label two 'B' and two 'b.' Cut and slide these together as you did for the first set, joining the 'B' chromatids together and the 'b' chromatids together. Repeat this process for the third set of chromatids, labeling them as 'D' and 'd.' You now have models for three pairs of homologous chromosomes, for a total of six chromosomes. Separate the chromosomes as though meiotic anaphase I and telophase I have taken place.

Verified step by step guidance

Step 1: Understand the setup of the problem. You are creating a physical model of chromosomes to simulate the process of meiosis. Each set of chromatids represents homologous chromosomes, and you will manipulate them to mimic the stages of meiosis.

Step 2: Begin by separating the chromatids into three sets of four. Label the chromatids in each set as instructed: 'A' and 'a' for the first set, 'B' and 'b' for the second set, and 'D' and 'd' for the third set. Ensure that each pair of chromatids in a set is identical in size and shape.

Step 3: Simulate the formation of sister chromatids by cutting each chromatid halfway across near the midpoint and sliding the two chromatids of the same label together. For example, slide the two 'A' chromatids together to form a pair of sister chromatids, and do the same for 'a,' 'B,' 'b,' 'D,' and 'd.' You now have three pairs of homologous chromosomes.

Step 4: To simulate meiotic anaphase I, separate the homologous chromosomes from each other. For example, move the 'A'/'A' sister chromatids to one side and the 'a'/'a' sister chromatids to the opposite side. Repeat this for the 'B'/'B' and 'b'/'b' pairs, as well as the 'D'/'D' and 'd'/'d' pairs.

Step 5: To simulate telophase I, group the separated chromosomes into two distinct sets, representing the two daughter cells formed at the end of meiosis I. Each daughter cell should now contain one chromosome from each homologous pair (e.g., one cell might have 'A,' 'B,' and 'D,' while the other has 'a,' 'b,' and 'd').

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chromatids

Chromatids are the two identical halves of a replicated chromosome, which are joined together at a region called the centromere. During cell division, specifically in mitosis and meiosis, chromatids play a crucial role in ensuring that genetic material is accurately distributed to daughter cells. Each chromatid contains a single DNA molecule, and they are essential for the proper segregation of chromosomes during cell division.

Homologous Chromosomes

Homologous chromosomes are pairs of chromosomes that have the same structure and carry genes for the same traits, but may have different alleles. One chromosome of each pair is inherited from each parent, and during meiosis, these homologous chromosomes undergo processes such as crossing over and independent assortment, which contribute to genetic diversity in gametes. Understanding homologous chromosomes is vital for grasping how genetic variation occurs during reproduction.

Meiosis

Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in the formation of gametes (sperm and eggs). It consists of two sequential divisions: meiosis I and meiosis II. During meiosis I, homologous chromosomes are separated, while meiosis II separates sister chromatids. This process is essential for sexual reproduction, as it ensures that offspring receive a mix of genetic material from both parents.

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Textbook Question

From a piece of blank paper, cut out three sets of four cigar-shaped structures (a total of 12 structures). These will represent chromatids. Be sure each member of a set of four chromatids has the same length and girth. In set one, label two chromatids 'A' and two chromatids 'a.' Cut each of these chromatids about halfway across near their midpoint and slide the two 'A' chromatids together at the cuts to form a single set of attached sister chromatids. Do the same for the 'a' chromatids. In the second set of four chromatids, label two 'B' and two 'b.' Cut and slide these together as you did for the first set, joining the 'B' chromatids together and the 'b' chromatids together. Repeat this process for the third set of chromatids, labeling them as 'D' and 'd.' You now have models for three pairs of homologous chromosomes, for a total of six chromosomes. What are the genotypes of the daughter cells?

From a piece of blank paper, cut out three sets of four cigar-shaped structures (a total of 12 structures). These will represent chromatids. Be sure each member of a set of four chromatids has the same length and girth. In set one, label two chromatids 'A' and two chromatids 'a.' Cut each of these chromatids about halfway across near their midpoint and slide the two 'A' chromatids together at the cuts, to form a single set of attached sister chromatids. Do the same for the 'a' chromatids. In the second set of four chromatids, label two 'B' and two 'b.' Cut and slide these together as you did for the first set, joining the 'B' chromatids together and the 'b' chromatids together. Repeat this process for the third set of chromatids, labeling them as 'D' and 'd.' You now have models for three pairs of homologous chromosomes, for a total of six chromosomes. Align the chromosomes of each daughter cell as they might appear in metaphase II of meiosis.

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Textbook Question

From a piece of blank paper, cut out three sets of four cigar-shaped structures (a total of 12 structures). These will represent chromatids. Be sure each member of a set of four chromatids has the same length and girth. In set one, label two chromatids 'A' and two chromatids 'a.' Cut each of these chromatids about halfway across near their midpoint and slide the two 'A' chromatids together at the cuts, to form a single set of attached sister chromatids. Do the same for the 'a' chromatids. In the second set of four chromatids, label two 'B' and two 'b.' Cut and slide these together as you did for the first set, joining the 'B' chromatids together and the 'b' chromatids together. Repeat this process for the third set of chromatids, labeling them as 'D' and 'd.' You now have models for three pairs of homologous chromosomes, for a total of six chromosomes. Are there any alternative alignments of the chromosomes for this cell-division stage? Explain.

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Textbook Question

From a piece of blank paper, cut out three sets of four cigar-shaped structures (a total of 12 structures). These will represent chromatids. Be sure each member of a set of four chromatids has the same length and girth. In set one, label two chromatids 'A' and two chromatids 'a.' Cut each of these chromatids about halfway across near their midpoint and slide the two 'A' chromatids together at the cuts, to form a single set of attached sister chromatids. Do the same for the 'a' chromatids. In the second set of four chromatids, label two 'B' and two 'b.' Cut and slide these together as you did for the first set, joining the 'B' chromatids together and the 'b' chromatids together. Repeat this process for the third set of chromatids, labeling them as 'D' and 'd.' You now have models for three pairs of homologous chromosomes, for a total of six chromosomes. Align the chromosomes as they might appear at metaphase I of meiosis.