Chapter 3, Problem 1P

Examine the following diagrams of cells from an organism with diploid number 2n = 6, and identify what stage of M phase is represented.

Summary Introduction

To review:

Identification of stages of mitotic or meiotic phase from the given diagrams in question.

Introduction:

There are two types of cell division – mitosis and meiosis. Somatic cell division is termed as mitosis, and germ cell division is termed as meiosis. The prophase, metaphase, anaphase, and telophase are four phases in mitosis. In prophase, chromatin gets condensed and chromosomes become visible under microscope. In metaphase, homologous chromosomes get aligned in the center of the cell. In anaphase, sister chromatids are separated by mitotic spindles. The last phase is telophase in which a nuclear membrane is formed between daughter cells; a cleavage furrow is formed which separates the cytoplasm of the parent cell equally, and diploid daughter cells are formed from diploid parent cells.

Meiosis 1 and meiosis 2 are the two cycles in meiosis. Meiosis 1 is known as reduction division. The rare event of crossing over occurs in this phase in which segments of non-sister chromatids are exchanged. Meiosis 1 results in two haploid daughter cells, and then meiosis 2 begins, which forms 4 haploid cells.

Explanation of Solution

The given diagram is of anaphase 1. The given diagram shows that the homologous chromosomes get pulled by microtubules and move to opposite poles. This phenomenon is observed in both types of cell division (mitosis and meiosis), but here, segments of chromosomes are shown in different colors, which means crossing over takes place between them, and crossing over is s rare phenomenon, which occurs in meiosis 1 (Anaphase 1) only.

The given diagram is of metaphase. It can be concluded by observing the position of chromosomes. In the given diagram, chromosomes are aligned in the middle of the cell.

The given diagram is of cytokinesis (telophase). Cleavage furrow is formed between daughter cells which separates parent cytoplasm equally into two daughter cells. Initiation of nuclear membrane formation is observed.

Given diagram is of anaphase. Initiation of movement of sister chromatids to apposite pole is observed as sister chromatids get pulled by mitotic spindles. Crossing over is not observed.

Conclusion

1. The given diagram is of anaphase 1.

2. The given diagram is of metaphase.

3. The given diagram is of cytokinesis (telophase).

4. The given diagram is of anaphase.