Question

Which of the following is a term for a plant or an embryo that contains only a gametic chromosome set:

• A. Monoploid
• B. Aneuploid
• C. Haploid
• D. Gametophyte

Hint:

Remember:
\(n\) = Haploid (gametic chromosome set)
\(x\) = Monoploid (basic chromosome set)
In polyploids, \(n\) is not equal to \(x\), which makes "Haploid" the correct term for gametic chromosome sets.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The chromosome number of an organism is defined relative to its lifecycle stages and ploidy levels.
The somatic chromosome number of a diploid sporophyte is represented as \(2n\), while the gametic chromosome number found in the gametes (pollen or egg) is represented as \(n\).

Step 2: Detailed Explanation:
Let us evaluate each cytogenetic term:
- Haploid (C): A haploid cell, embryo, or plant possesses exactly the gametic chromosome number (\(n\)) characteristic of the species.
Regardless of whether the species is a simple diploid or a complex polyploid, any individual that develops directly from a gamete (such as through parthenogenesis or androgenesis) and contains only the gametic chromosome complement is referred to as a haploid.
- Monoploid (A): A monoploid organism contains a single basic set of chromosomes (\(x\)).
In a simple diploid species, the monoploid number is equal to the haploid number (\(n = x\)).
However, in polyploids, such as hexaploid wheat (\(2n = 6x = 42\)), the haploid gametic number is \(n = 3x = 21\), which contains three basic chromosome sets, whereas the monoploid number remains \(x = 7\).
Therefore, "containing only a gametic chromosome set" is the definition of a haploid.
- Aneuploid (B): Aneuploids have a chromosome number that is not an exact multiple of the basic set due to the loss or gain of individual chromosomes (e.g., \(2n-1\), \(2n+1\)).
- Gametophyte (D): A gametophyte is the haploid, gamete-producing multicellular phase in the alternation of generations of plants, but it is a lifecycle stage rather than a specific term for an abnormal sporophytic embryo containing gametic chromosomes.

Step 3: Final Answer:
Haploid is the correct term.