If the number of bivalents is 10 in prophase - l what will be the number of the chromosomes during late anaphase - II in each cell ?

Options

A. 10 with two chromatids each
B. 10 with one chromatid each
C. 20 with two chromatids each
D. 20 with one chromatid each

Answer

To solve the question, we need to analyze the situation step by step.

### Step 1: Understand the concept of bivalents
- In prophase I of meiosis, homologous chromosomes pair up to form structures called bivalents. Each bivalent consists of two homologous chromosomes, each made up of two sister chromatids.
- Given that the number of bivalents is 10, this means there are 10 pairs of homologous chromosomes.

### Step 2: Determine the total number of chromosomes in prophase I
- Since each bivalent consists of 2 homologous chromosomes, the total number of chromosomes during prophase I can be calculated as:
\[ \text{Total chromosomes} = \text{Number of bivalents} \times 2 = 10 \times 2 = 20 \]
- Therefore, there are 20 chromosomes in prophase I, each consisting of 2 sister chromatids.

### Step 3: Transition to anaphase II
- During meiosis, the process involves two rounds of division: meiosis I and meiosis II.
- In anaphase II, the sister chromatids of each chromosome separate and move towards opposite poles of the cell.
- After the separation of sister chromatids, each chromatid is considered an individual chromosome.

### Step 4: Calculate the number of chromosomes in late anaphase II
- Since there were 20 chromosomes in prophase I (each with 2 chromatids), after meiosis I, the number of chromosomes is halved:
\[ \text{Number of chromosomes after meiosis I} = \frac{20}{2} = 10 \]
- In anaphase II, each of these 10 chromosomes will separate into 10 individual chromatids, which are now considered as individual chromosomes.
- Therefore, during late anaphase II, the number of chromosomes will be:
\[ \text{Total chromosomes in late anaphase II} = 10 \text{ (each with 1 chromatid)} \]

### Final Answer
- The number of chromosomes during late anaphase II in each cell is **10 with one chromatid each**.

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