Question

Arrange the following parts of Wheat (Triticum aestivum L.) in descending order with respect to their chromosome number:
A. Endosperm
B. Male gamete
C. Embryo

• A. B, A, C
• B. C, A, B
• C. A, C, B
• D. A, B, C

Hint:

Ploidy level of tissues in hexaploid wheat ($n=21$):
- Male Female Gamete: Haploid ($n = 21$)
- Root Tip Embryo Leaves: Diploid ($2n = 42$)
- Endosperm: Triploid ($3n = 63$)

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Common bread wheat (Triticum aestivum) is an allohexaploid species ($2n = 6x = 42$).
Different parts of the seed and plant have different ploidy levels based on their origin during double fertilization.

Step 2: Detailed Explanation:
Let us determine the ploidy and chromosome number for each of the given parts:
A. Endosperm:
In angiosperms, the endosperm is formed via triple fusion, which is the fusion of two haploid polar nuclei ($2 \times n$) and one haploid male gamete ($1 \times n$).
This results in a triploid ($3n$) tissue.
For hexaploid wheat where:
\[ n = 21 \]
The endosperm chromosome number is:
\[ 3n = 3 \times 21 = 63 \]
C. Embryo:
The embryo is formed by the fusion of one haploid egg cell ($n$) and one haploid male gamete ($n$), resulting in a diploid ($2n$) zygote.
For hexaploid wheat, the embryo chromosome number is:
\[ 2n = 2 \times 21 = 42 \]
B. Male gamete:
The male gamete (sperm cell) is haploid ($n$) and is produced by the mitotic division of the generative cell within the pollen grain.
Its chromosome number is:
\[ n = 21 \]

Step 3: Final Answer:
Arranging these parts in descending order of their chromosome number:
Endosperm ($63$) $>$ Embryo ($42$) $>$ Male gamete ($21$).
This corresponds to the sequence A, C, B, which is Option (C).