9. Mitosis and Meiosis

Mitosis

9. Mitosis and Meiosis

Mitosis

3:25 minutes

Problem 32l

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?

Verified step by step guidance

Step 1: Understand the concept of homologous chromosomes and sister chromatids. Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that have the same genes but may have different alleles. Sister chromatids are identical copies of a single chromosome, formed during DNA replication.

Step 2: Recognize that the labeling ('A' and 'a', 'B' and 'b', 'D' and 'd') represents alleles of genes on homologous chromosomes. 'A' and 'a' are alleles for one gene, 'B' and 'b' for another, and 'D' and 'd' for a third gene.

Step 3: Note that the process described involves creating models of homologous chromosomes by pairing sister chromatids ('A' with 'A', 'a' with 'a', etc.) and grouping homologous pairs ('A/a', 'B/b', 'D/d'). This setup represents the chromosomes before cell division.

Step 4: Consider the type of cell division that will occur. If this is mitosis, the daughter cells will receive identical sets of chromosomes, maintaining the same genotype as the parent cell. If this is meiosis, homologous chromosomes will separate during meiosis I, and sister chromatids will separate during meiosis II, leading to daughter cells with different combinations of alleles.

Step 5: To determine the genotypes of the daughter cells, analyze the segregation of alleles during meiosis. For example, if the parent cell is heterozygous for all three genes (AaBbDd), the daughter cells could have combinations such as ABD, AbD, aBD, or abD, depending on how the alleles segregate during meiosis.

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Key Concepts

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

Chromatids and Chromosomes

Chromatids are the two identical halves of a replicated chromosome, joined together at a region called the centromere. During cell division, specifically in meiosis, these chromatids separate to ensure that each daughter cell receives the correct number of chromosomes. Understanding the structure and behavior of chromatids is essential for predicting the genetic makeup of daughter cells.

Homologous Chromosomes

Homologous chromosomes are pairs of chromosomes that have the same structure and gene sequence but may carry different alleles. In the context of the question, the sets labeled 'A', 'a', 'B', 'b', 'D', and 'd' represent different alleles of the same genes on homologous chromosomes. This concept is crucial for determining the genotypes of daughter cells after meiosis, as it influences genetic variation.

Genotype and Alleles

A genotype refers to the genetic constitution of an organism, specifically the alleles present for a given gene. In this scenario, the daughter cells will inherit combinations of the alleles from the parent chromatids, leading to various genotypes. Understanding how alleles combine during cell division is key to predicting the genetic outcomes in the daughter cells.

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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.

403

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

407

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 anaphase II and telophase II have taken place.

396

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.

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.

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