Problem 6 - Biology Concepts and Applications

Question

Sister chromatids of each duplicated chromosome separate during ________. a. prophase I b. prophase II c. anaphase I d. anaphase II e. both b and \(c\)

Step-by-Step Solution

Answer

d. anaphase II

Step 1: Understanding Chromosome Separation in Meiosis

Meiosis consists of two divisions: meiosis I and meiosis II. In meiosis I, homologous chromosomes are separated, whereas in meiosis II, the sister chromatids are separated.

Step 2: Identifying the Phase of Separation

Sister chromatids are held together after replication during the S phase and stay connected until they are separated. This separation occurs in anaphase II during meiosis II.

Step 3: Evaluating Each Option

- **a. prophase I:** This phase involves the condensation of chromosomes but not their separation. - **b. prophase II:** Similar to prophase I, this phase involves preparation for separation but is not when separation occurs. - **c. anaphase I:** During anaphase I, homologous chromosomes, not sister chromatids, are separated. - **d. anaphase II:** This is when sister chromatids are actually separated in meiosis II. - **e. both b and c:** This is incorrect because sister chromatids do not separate during prophase II or anaphase I.

Step 4: Selecting the Correct Answer

The correct answer is **d. anaphase II**, as this phase specifically involves the separation of sister chromatids into individual chromosomes during meiosis II.

Key Concepts

Sister Chromatids

Sister chromatids are two identical copies of a single replicated chromosome, connected by a structure called the centromere. Each chromatid consists of a DNA molecule that was replicated during the S phase of the cell cycle.
Together, they are crucial for the accurate distribution of genetic material during cell division. Sister chromatids ensure that each new cell receives a complete set of chromosomes.

• They are formed during the S phase of the interphase, when the DNA is replicated.
• They remain attached at the centromere until they are separated during cell division.
• Their structure is critical for the functioning of the mitotic spindle during division.

Chromosome Separation

During meiosis, chromosome separation occurs twice, once in each meiotic division: meiosis I and meiosis II. In meiosis I, homologous chromosomes are separated. This ensures that each cell gets one set of chromosomes.
In meiosis II, it's the sister chromatids' turn to separate, ensuring that each daughter cell is a haploid – containing a single set of chromosomes.

• In meiosis I, homologous chromosomes are separated into two cells.
• In meiosis II, the sister chromatids are separated into four different cells.
• This precise separation is crucial for genetic diversity and stability.

Anaphase II

Anaphase II is a critical phase in meiosis II where the actual separation of sister chromatids takes place. At this stage, microtubules pull the sister chromatids towards opposite poles of the cell.
This action is essential for ensuring that each of the resulting daughter cells receives an identical set of chromosomes.

• During anaphase II, centromeres split, allowing sister chromatids to finally part ways.
• The chromatids, now individual chromosomes, are pulled to opposite poles.
• This step follows metaphase II, where chromosomes align at the metaphase plate.

Understanding the role of anaphase II in meiosis helps grasp how genetic information is distributed accurately, preparing for increased diversity through formation of gametes.