Question

In a population of a grasshopper species, the chromosome number of some members is 23 and some other members possess 24 chromosomes. The 23 and 24 chromosome-bearing members in this species are ________

• A. females and males, respectively
• B. all males
• C. males and females, respectively
• D. all females

Hint:

Logic Tip: In the XX-XO system, the male is always the one "missing" a chromosome. If you see a species with 23 and 24 chromosomes, the odd, lower number (23) is always the male (XO).

Answer 1

The Correct Option is C

Step 1 : Understanding the Question:
The question presents a scenario where different individuals of the same grasshopper species have different total chromosome counts (23 and 24). We need to determine which count belongs to the male and which belongs to the female based on known sex determination mechanisms in insects.
Step 2 : Key Formulas and Approach:
The approach involves identifying the specific chromosomal sex-determination system for grasshoppers:
1. Mechanism Identification: Grasshoppers follow the XX-XO system.
2. Male Genotype: XO (Heterogametic—they produce two types of sperm, one with X and one without).
3. Female Genotype: XX (Homogametic—all eggs carry an X).
4. Rule: Total Chromosomes = Autosomes + Sex Chromosomes.
Step 3 : Detailed Explanation:

Mechanism Details: In the XX-XO system used by grasshoppers and many other insects, sex is determined by the number of X chromosomes. Females possess a pair of X chromosomes (XX), while males possess only a single X chromosome (XO). The "O" denotes the absence of a partner chromosome.

Female Chromosome Count: Since females have two X chromosomes (a complete pair), their total chromosome count will always be an even number. If the species has 22 autosomes, the female count is $22 (A) + 2 (XX) = 24$.

Male Chromosome Count: Males have the same number of autosomes but only one X chromosome and no Y or second X. Therefore, they are "short" one chromosome compared to the female. Their total count will always be an odd number. In this case, the male count would be $22 (A) + 1 (X) = 23$.

Logic Check: The question states some members have 23 and some have 24. Following the XX-XO logic, the members with 23 chromosomes (the odd number) must be the males, and those with 24 (the even number) must be the females.

Step 4 : Final Answer:
Therefore, the 23-chromosome members are males and the 24-chromosome members are females. Following the "respectively" order, the correct answer is option (C).