9. Mitosis and Meiosis

Mitosis

9. Mitosis and Meiosis

Mitosis

2:39 minutes

Problem 32k

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 anaphase II and telophase II 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 are tasked with separating them as they would during anaphase II and telophase II.

Step 2: Recall the key events of anaphase II. During this stage of meiosis, the sister chromatids of each chromosome are pulled apart by spindle fibers and move toward opposite poles of the cell. This means that each chromatid (e.g., 'A' and 'a') will separate from its sister chromatid and move to opposite sides.

Step 3: Physically separate the chromatids in each pair. For the first set, separate the 'A' chromatids from each other and the 'a' chromatids from each other. Repeat this process for the second set ('B' and 'b') and the third set ('D' and 'd'). Ensure that each chromatid is now on its own and no longer attached to its sister chromatid.

Step 4: Simulate telophase II. In this stage, the separated chromatids are now considered individual chromosomes. Place the separated chromatids into four distinct groups, representing the four haploid daughter cells that result from meiosis II. Each group should contain one chromatid from each homologous pair (e.g., one 'A,' one 'B,' and one 'D' in one group).

Step 5: Verify the results. Ensure that each of the four groups contains one chromatid from each homologous pair ('A' or 'a,' 'B' or 'b,' and 'D' or 'd'). This represents the genetic diversity achieved through meiosis, as each haploid cell contains a unique combination of chromatids.

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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. In the context of the question, the cigar-shaped structures represent chromatids that will be manipulated to model chromosome behavior 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. Each pair consists of one chromosome inherited from each parent. In the exercise described, the sets of chromatids labeled 'A', 'a', 'B', 'b', 'D', and 'd' represent homologous chromosomes, which are essential for understanding genetic variation and inheritance during meiosis.

Anaphase II and Telophase II

Anaphase II and Telophase II are stages of meiosis, the process of cell division that produces gametes. During Anaphase II, sister chromatids are pulled apart to opposite poles of the cell, while in Telophase II, the separated chromatids reach the poles, and the cell begins to divide. Understanding these stages is crucial for visualizing how genetic material is segregated and how gametes are formed, which is the focus of the exercise in the question.

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Textbook Question

A species of cereal rye (Secale cereale) has a chromosome number of 14, while a species of Canadian wild rye (Elymus canadensis) has a chromosome number of 28. Sterile hybrids can be produced by crossing Secale with Elymus.

What would be the expected chromosome number in the somatic cells of the hybrids?

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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. Combining your work in steps (f) through (m), provide a written explanation of the connection between meiotic cell division and Mendel's law of independent assortment.

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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. Repeat steps (h) through (l) for the alternative alignment of chromosomes you identified in step (g).

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.

437

views

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 of each daughter cell as they might appear in metaphase II of meiosis.

386

views

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.

386

views

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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