Question

Study the following statements regarding genic balance theory and identify incorrect statements: A) The production of gametes with abnormal number of chromosomes is due to non-disjunction. B) In Drosophila 'XO' males produce motile sperms. C) Sex index < 0.5 indicates intersexes in Drosophila. D) 'Y' chromosome in Drosophila lacks testis determining factor.

• A. A & C
• B. A & D
• C. B & C
• D. B & D

Hint:

In Drosophila, XO is a sterile male; the Y chromosome is for fertility only.

Answer 1

The Correct Option is C

Step 1: The task.
This is about the genic balance theory of sex determination in Drosophila, and we must find the wrong statements.

Step 2: Statement A.
Gametes with the wrong number of chromosomes form when chromosomes fail to separate properly, called non-disjunction. This is correct, so A is not a wrong statement.

Step 3: Statement B.
An XO fly in Drosophila is a male in appearance, but it is sterile and does not make motile (moving) sperms. So saying XO males produce motile sperms is wrong. B is incorrect.

Step 4: Statement C.
Sex is decided by the ratio of X chromosomes to autosome sets (the sex index). A value below 0.5 gives a male, while a value between 0.5 and 1.0 gives an intersex. So saying index less than 0.5 means intersex is wrong. C is incorrect.

Step 5: Statement D.
In Drosophila the Y chromosome does not carry a testis determining factor, sex depends on the X to autosome balance. So D is correct, not a wrong statement.

Step 6: Conclusion.
The incorrect statements are B and C, so the answer is "B & C". \[ \boxed{\text{B and C}} \]