If root cells have 18 chromosomes it is most likely that:

Options

A. gametes will have 18 chromosomes
B. gametes will have 9 chromosomes
C. zygotes will have 27 chromosomes
D. zygotes will have 9 chromosomes

Answer

To solve the question regarding the number of chromosomes in root cells and their implications for gametes and zygotes, we will follow these steps:

### Step-by-Step Solution:

1. **Understanding Chromosome Number in Root Cells**:
- The question states that root cells have 18 chromosomes. In terms of cell biology, this number represents the diploid (2n) chromosome count for these cells.

2. **Determining the Gamete Chromosome Count**:
- Gametes are reproductive cells (sperm and eggs) that are haploid (n), meaning they contain half the number of chromosomes compared to diploid cells.
- Since the root cells are diploid with 18 chromosomes (2n = 18), we can find the haploid number by dividing by 2.
- Calculation:
\[ n = \frac{2n}{2} = \frac{18}{2} = 9 \]
- Therefore, the gametes will have 9 chromosomes.

3. **Analyzing the Zygote Chromosome Count**:
- A zygote is formed when two gametes fuse during fertilization. Thus, the zygote will have the diploid number of chromosomes, which is the sum of the chromosomes from both gametes.
- Since each gamete has 9 chromosomes, the zygote will have:
- Calculation:
\[ 2n = n + n = 9 + 9 = 18 \]
- Therefore, the zygote will have 18 chromosomes, not 27 or 9.

4. **Conclusion**:
- Based on the analysis, the correct answer to the question is that gametes will have 9 chromosomes (option B).

### Final Answer:
**B. Gametes will have 9 chromosomes.**