Chapter 10, Problem 5A

Summary Introduction

Introduction:

In animals the sexual life cycle involves meiosis. Meiosis involves two consecutive cell divisions called meiosis I and meiosis II. In meiosis I the stages are interphase I, prophase I, metaphase I, anaphase I and telophase I. during interphase I cells carry out cellular activities, replication of DNA and synthesis of proteins.

Answer to Problem 5A

Correct answer :

The correct answer is option D. metaphase II

Explanation of Solution

Explanation/justification for the correct answer:

OptionD. metaphase II- This is the second stage in meiosis II. In this phase the haploid chromosomes line up at the cell’s equator. The spindle fibers attach to the centromere of each chromosome. As can be seen in the given diagram, the haploid chromosomes are lined up at the equator of the cell. Hence, this is the correct option.

Explanation for incorrect answer:

Option A. prophase I- During this process the replicated chromosomes appear as two sister chromatids. The homologous chromosomes condense and begin to form pairs in a process called synapsis. Some segments of homologous chromosomes get exchanged during synapsis. This process is called crossing over. In this phase the chromosomes do not line up at the cell’s equator. Hence, this is not the correct option.

Option B. prophase II- In this phase the chromosomes do not line up at the cell’s equator. A second set of phases start with spindle apparatus being formed and the chromosomes condense. Hence, this is not the correct option.

Option C. metaphase I- This is the second stage in meiosis I. In this phase the pairs of homologous chromosomes line up at the cell’s equator. The spindle fibers attach to the centromere of each homologous chromosome. As can be seen in the given diagram, the pairs of homologous chromosomes are not lined up at the equator of the cell. Only haploid chromosomes are lined up at the equator. Hence, this is not the correct option.