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 situation step by step:

### Step 1: Understand the Chromosome Number in the Zygote
The problem states that the zygote of the plant has 20 chromosomes. This indicates that the diploid (2n) chromosome number is 20. Therefore, we can determine the haploid (n) chromosome number:
- **Diploid (2n) = 20**
- **Haploid (n) = 20/2 = 10**

### Step 2: Identify the Type of Gametophyte Development
The female gametophyte of the plant develops aposporously. Apospory means that the gametophyte develops from diploid cells without undergoing meiosis. This implies that the embryo sac (which contains the egg) will also be diploid (2n).

### Step 3: Determine the Chromosome Number in the Egg
Since the embryo sac is diploid due to aposporous development, the egg cell within the embryo sac will also be diploid (2n). Therefore, the egg cell will have:
- **Egg cell = 2n = 20 chromosomes**

### Step 4: Cross with a Normal Male Plant
When this plant is crossed with a normal male plant, the male gamete (pollen grain) will be haploid (n). The normal male plant has a haploid number of chromosomes:
- **Male gamete = n = 10 chromosomes**

### Step 5: Calculate the Chromosome Number in the Zygote
During fertilization, the male gamete (n = 10) fuses with the diploid egg cell (2n = 20). The zygote will therefore have:
- **Zygote = Egg cell (2n) + Male gamete (n) = 20 + 10 = 30 chromosomes**
- Thus, the zygote will be triploid (3n).

### Step 6: Determine the Endosperm Chromosome Number
In flowering plants, double fertilization occurs. One male gamete fuses with the egg to form the zygote, and the other male gamete fuses with the two polar nuclei in the central cell of the embryo sac. Since the embryo sac is diploid (2n = 20), the central cell has:
- **Central cell = 2n = 20 chromosomes**

The other male gamete (n = 10) will fuse with the central cell (2n = 20):
- **Endosperm = Central cell (2n) + Male gamete (n) = 20 + 10 = 30 chromosomes**
- Thus, the endosperm will be triploid (3n).

### Final Answer
- **Number of chromosomes in the zygote = 30**
- **Number of chromosomes in the endosperm = 30**

### Summary
- Zygote: 30 chromosomes (3n)
- Endosperm: 30 chromosomes (3n)