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Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation1 Mark
Question
For question two statements are given-one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both assertion and reason are true and reason is the correct explanation of assertion.
  2. Both assertion and reason are true but reason is not the correct explanation of assertion.
  3. Assertion is true but reason is false.
  4. Both assertion and reason are false.
Assertion: In some Drosophila, bilateral gynandromorphs are found.
Reason: The gynandromorphs are formed by an irregularity in mitosis at the first cleavage of the zygote.
✓

Answer

  1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Abnormal chromosomal behaviour in insects can result in the formation of gynandromorphs or sexual mosaics in which some parts of the animal are female and other parts are male. Some gynandromorphs in Drosophila are bilateral intersex. Bilateral gynandromorphs have been explained on the basis of an irregularity in mitosis at the first cleavage of the zygote. Infrequently a chromosome lags in division and does not arrive at the pole in time to be included in the reconstructed nucleus. When one of the X chromosomes of an XX (female) zygote lags in the spindle, one daughter nucleus receives two X chromosomes. A mosaic body pattern is thus established. One nucleus in the nuclei stage would be XX (female) and one would be XO (male).

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