Question

At which stage of meiosis are sister chromatids separated from each other? a. prophase I b. prophase II c. anaphase I d. anaphase II

Short answer

Answer: d. anaphase II

Step-by-step solution

Understand the phases of meiosis

Meiosis is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell. It consists of two divisions, meiosis I and meiosis II, each containing several stages: prophase, metaphase, anaphase, and telophase.

Review the events of meiosis I

In meiosis I, homologous chromosomes are separated. During prophase I, the chromosomes condense, and homologous chromosomes pair up. At the end of prophase I, the nuclear membrane breaks down. Metaphase I involves the alignment of homologous chromosomes at the center of the cell. In anaphase I, homologous chromosomes separate and move towards opposite poles of the cell. Finally, during telophase I, the chromosomes reach the poles, and the cell divides, resulting in two haploid daughter cells.

Review the events of meiosis II

Meiosis II is similar to mitosis, where the sister chromatids are separated. During prophase II, the chromosomes condense again, and the nuclear membrane breaks down. Metaphase II involves the alignment of chromosomes at the center of the cell. In anaphase II, sister chromatids separate and move towards opposite poles of the cell. Finally, during telophase II, the chromatids reach the poles, and the cell divides, resulting in four haploid daughter cells.

Determine the stage where sister chromatids separate

Based on the information in Steps 2 and 3, we can deduce that sister chromatids are separated during anaphase II of meiosis.

Provide the answer

The stage of meiosis when sister chromatids are separated from each other is: d. anaphase II

Key concepts

Anaphase II

In meiosis, the step where sister chromatids finally part ways is called anaphase II. After chromosomes condense and align at the cell's equator during metaphase II, anaphase II follows. This phase is crucial for ensuring that each new cell will have just one copy of each chromosome.

Imagine a classroom where students are paired to share a textbook. During anaphase II, it's like each student gets their own book to take home. Centromeres split, and the sister chromatids (now individual chromosomes) are pulled apart by spindle fibers to opposite ends of the cell. This is the heart of genetic diversity; each chromatid is unique due to genetic recombination in meiosis I, meaning each new cell is also genetically unique.

Understanding this stage is key in grasping the overall process of meiosis, as it sets the stage for the final cell divisions that eventually lead to the formation of gametes (sperm and egg cells).

Sister Chromatid Separation

Sister chromatid separation marks the defining moment that paves the path to forming new cells with varied genetic combinations. Sister chromatids are identical copies of a single chromosome, originally joined together. It's crucial to grasp that this separation occurs in anaphase II of meiosis and results in the reduction of chromosome numbers by half—this is what ensures genetic diversity among sexually reproducing organisms.

Analogy for Understanding

Think of each pair of sister chromatids like twins holding hands. The process of meiosis is like a journey where, eventually, these twins go off on separate paths. When they do split during anaphase II, they carry with them a unique set of genetic instructions critical for the development of unique organisms.

Highlighting the distinction between anaphase I, where homologous chromosomes separate, and anaphase II, where sister chromatids divide, helps students deepen their understanding of meiosis and the fascinating genetic ballet that orchestrates life.

Meiosis I

Meiosis I is the first leg of the meiosis journey, wherein one cell starts the complex process of becoming four. It's characterized mainly by the separation of homologous chromosomes—pairs of similar yet not identical chromosomes inherited from each parent.

This process kicks off with prophase I, where chromosomes condense, and genetic material is shuffled in a process called 'crossing over.' Metaphase I follows, lining up pairs at the cell's midpoint. Anaphase I sees these pairs part ways, and by telophase I, the cell splits into two. It's a dance of DNA, choreographed to introduce genetic variety.

Meiosis I is often where students need clarity—it's fundamentally different from meiosis II because it's about separating chromosome types, not identical copies. It's also vital as it's responsible for the genetic variation foundational to evolution and species survival.

Meiosis II

If meiosis I is about diversity, meiosis II is about halving the chromosome number. Here, cells produced from meiosis I embark on a journey similar to mitosis, with a key distinction—they're reducing already halved genetic material.

Beginning with prophase II, the cells prepare their condensed chromosomes for another split. Metaphase II aligns them in the center, ready for the big event. Anaphase II is where sister chromatids finally separate, as explained earlier, and by telophase II, we're nearing the end of this genetic odyssey.

Understanding meiosis II is critical for students as it explains how organisms produce cells with the correct number of chromosomes for sexual reproduction. This ensures that when fertilization occurs, the resulting offspring will have a complete set of chromosomes — half from each parent. It's a perfect blend of the two cellular narratives of meiosis I and II culminating in the fundamental purpose of this biological process—reproduction and biodiversity.