Chapter 12, Problem 2STP

Summary Introduction

Introduction:

In animals the sexual life cycle involves meiosis. Meiosis involves two consecutive cell divisions called meiosis I and meiosis II. The two divisions produce a set of four haploid daughter cells that are not identical. Meiosis is important because it results in genetic variation.

Answer to Problem 2STP

Correct answer :

The correct answer is option A. anaphase I

Explanation of Solution

Explanation/justification for the correct answer:

Option A. anaphase I− During anaphase I, as can be seen in the given diagram, the homologous chromosomes separate and line up at the equator of the cell. Each member of the pair is guided by spindle fibers. The spindle fibers attach to the centromere of each chromosome. The homologous chromosomes then move towards the opposite poles of the cell. Each homologous chromosome still consist of two sister chromatids. Hence this is the correct option.

Explanation for incorrect answer:

Option B. anaphase II- After anaphase II, the sister chromatids separate and move to opposite poles of the cells. Here the chromosomes can be clearly seen to be having two sister chromatids. Hence this is not the correct option.

Option C. metaphase I- In metaphase I, the homologous chromosomes simply line up at the equator. They do not separate as can be seen in the diagram. Hence this is not the correct option.

Option D. metaphase II- In metaphase II, the centromeres of chromosomes simply line up at the equator. The chromosomes do not separate as can be seen in the diagram. Hence this is not the correct option.