Suppose there are 20 chromosomes in zygote of a plant and its female gametophyte develops aposporously. Now this plant is crossed with a normal male plant. What will be the number of chromosomes in its zygote and endosperm respectively ?

Options

A. 30 and 50
B. 20 and 30
C. 30 and 30
D. 40 and 50

Answer

To solve the problem, we need to analyze the information provided step by step:

### Step 1: Understand the Chromosome Count in the Zygote
- The problem states that the zygote of the plant has 20 chromosomes.
- This indicates that the zygote is diploid (2n), meaning it has two sets of chromosomes. Therefore, we can conclude that:
\[ 2n = 20 \implies n = 10 \]
Here, \( n \) represents the haploid number of chromosomes.

### Step 2: Analyze the Female Gametophyte Development
- The female gametophyte develops aposporously, which means it does not undergo meiosis.
- Normally, meiosis would reduce the chromosome number, but since it develops aposporously, the female gamete retains the diploid state.
- Thus, the female gamete will also have 20 chromosomes (2n = 20).

### Step 3: Determine the Male Gamete Contribution
- The male plant is normal, so it produces male gametes through meiosis.
- Therefore, the male gamete will have half the number of chromosomes compared to the zygote:
\[ n = 10 \]
Thus, the male gamete contributes 10 chromosomes.

### Step 4: Calculate the Chromosome Number in the Zygote After Fertilization
- During fertilization, the male gamete (n = 10) fuses with the female gamete (2n = 20).
- The total chromosome count in the zygote after fertilization will be:
\[ 20 (from female) + 10 (from male) = 30 \text{ chromosomes (3n)} \]

### Step 5: Analyze the Formation of Endosperm
- The endosperm is formed through a process called triple fusion, where the second male gamete fuses with the two polar nuclei in the female gametophyte.
- Since the female gametophyte develops aposporously, the polar nuclei will also be diploid (2n = 20).
- Therefore, each polar nucleus has 20 chromosomes, and since there are two polar nuclei:
\[ 20 + 20 = 40 \text{ chromosomes (4n)} \]
- The second male gamete (n = 10) fuses with the two polar nuclei (4n = 40):
\[ 40 + 10 = 50 \text{ chromosomes (5n)} \]

### Summary of Results
- The number of chromosomes in the zygote = 30
- The number of chromosomes in the endosperm = 50

### Final Answer
- **Zygote:** 30 chromosomes
- **Endosperm:** 50 chromosomes

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