Question

Based on the threshold range, at the X/A ratio of 0.67, the sex of {Drosophila will be:}

• A. Intersex
• B. Superfemale
• C. Supermale
• D. Male

Hint:

Memorize the key X/A ratio points for {Drosophila}: 1.0 is female, 0.5 is male. Anything between is intersex. Anything above 1.0 is superfemale, and below 0.5 is supermale. The Y chromosome in flies is important for male fertility but not for sex determination itself.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The sex of a {Drosophila melanogaster} (fruit fly) is determined by the Genic Balance Theory, proposed by Calvin Bridges. According to this theory, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes (X/A ratio).

Step 2: Key Formula or Approach:
The thresholds for the X/A ratio determine the sexual phenotype:

X/A Ratio \(\geq\) 1.0: Female (e.g., XX/2A = 1.0). If X/A>1.0 (e.g., XXX/2A = 1.5), it's a Superfemale (or metafemale), often sterile and weak.
X/A Ratio = 0.5: Male (e.g., XY/2A = 0.5).
X/A Ratio<0.5: Supermale (or metamale), sterile and weak.
X/A Ratio between 0.5 and 1.0: Intersex. These individuals display a mixture of male and female characteristics. \end{itemize}
Step 3: Detailed Explanation:
The question provides an X/A ratio of 0.67. We compare this value to the established thresholds:
\[ 0.5<0.67<1.0 \] Since the ratio falls between the value for a normal male (0.5) and a normal female (1.0), the resulting phenotype will be an Intersex. An example of a fly with this ratio would be one with two X chromosomes and three sets of autosomes (2X/3A \(\approx\) 0.67).

Step 4: Final Answer:
An X/A ratio of 0.67 in {Drosophila} results in an Intersex phenotype. Therefore, option (A) is correct.