Question

Sexual phenotype of Drosophila with the karyotype \(AA+XXX\) is:

• A. Female
• B. Metafemale
• C. Inter sex
• D. Triploid female

Hint:

For Drosophila: X/A = 1 gives female, X/A = 0.5 gives male, values greater than 1 produce metafemale.

Answer 1

The Correct Option is B

Concept: In Drosophila, sex determination depends upon the ratio of X chromosomes to sets of autosomes (X/A ratio). \[ \text{Sex Index}=\frac{\text{Number of X chromosomes}}{\text{Number of sets of autosomes}} \] Important values: \[ 1.0 = \text{Female} \] \[ 0.5 = \text{Male} \] \[ >1 = \text{Metafemale} \] \[ 0.5-1 = \text{Intersex} \]

Step 1: Determine the number of X chromosomes. The given genotype is \[ AA+XXX \] Number of X chromosomes \[ =3 \]

Step 2: Determine the number of autosomal sets. The notation \(AA\) indicates two sets of autosomes. Therefore, \[ A=2 \]

Step 3: Calculate the sex index. \[ \text{Sex Index} = \frac{3}{2} = 1.5 \]

Step 4: Interpret the result. Since \[ 1.5>1 \] the individual develops as a metafemale. \[ \boxed{\text{Metafemale}} \]