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

Concept:
Grasshoppers, along with many other insects like bugs and cockroaches, follow the XX-XO type of sex determination mechanism. This is a form of male heterogamety where the sexes have a different total number of chromosomes.
Step 1:
In this system, females possess two X chromosomes (XX) in addition to the autosomes. Males possess only one X chromosome (XO) in addition to the autosomes. The 'O' indicates the absence of a second sex chromosome.
Step 2:
Since females have a pair of sex chromosomes (XX), their total chromosome count will be an even number. Let $A$ be the number of autosomes. Female chromosome count = $A + 2$ (for XX). In this specific species, the female total is 24.
Step 3:
Males have only one sex chromosome (X). Therefore, their total chromosome count will be exactly one less than the female count. Male chromosome count = $A + 1$ (for X). If females have 24, males will have $24 - 1 = 23$.
Step 4:
The question asks to identify the 23 and 24 chromosome-bearing members, respectively. - 23 chromosomes = males. - 24 chromosomes = females. Therefore, the sequence is males and females.
Step 5:
Option (3) "males and females, respectively" correctly aligns with the XX-XO sex determination mechanism.