When a diploid female plant is crossed with a tetraploid male, the ploidy level of endosperm cells in the resulting seed is:

Options

A. tetrapolidy
B. pentaploidy
C. diploidy
D. tripolidy

Answer

To determine the ploidy level of the endosperm cells in the resulting seed when a diploid female plant is crossed with a tetraploid male, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Ploidy Levels of Parents**:
- The female plant is diploid (2n), meaning it has two sets of chromosomes.
- The male plant is tetraploid (4n), meaning it has four sets of chromosomes.

2. **Gamete Formation**:
- During gamete formation, the diploid female plant will produce haploid (n) gametes. This is because meiosis reduces the chromosome number by half.
- The tetraploid male plant will also produce haploid (n) gametes through the same process of meiosis.

3. **Fertilization**:
- When the haploid male gamete (n) fertilizes the haploid female gamete (n), the resulting zygote will have a diploid (2n) chromosome number.
- However, the endosperm is formed through a unique process called double fertilization.

4. **Double Fertilization**:
- In double fertilization, one male gamete fuses with the egg cell (producing the zygote, which is 2n), and the other male gamete fuses with the two polar nuclei present in the embryo sac.
- The polar nuclei are typically diploid (2n) in the case of a diploid female plant.

5. **Endosperm Formation**:
- The fusion of one male gamete (n) with the two polar nuclei (2n) results in the formation of the endosperm.
- Therefore, the ploidy level of the endosperm will be: n (from the male gamete) + 2n (from the polar nuclei) = 3n (triploid).

### Conclusion:
The ploidy level of the endosperm cells in the resulting seed is **triploidy (3n)**.

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