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Which of the following organisms does not exhibit X chromosome inactivation?

Option: 1


Option: 2

 Fruit flies (Drosophila melanogaster)

Option: 3

Cats (Felis catus)

Option: 4

Birds (Aves)

Answers (1)


In mammals, X chromosome inactivation occurs when one of the two X chromosomes in female cells is randomly inactivated to accomplish dosage adjustment between males and females. Birds (Aves) do not have X chromosomal inactivation. Both the Z and W chromosomes are sex chromosomes in birds, with females having ZW and males having ZZ. Unlike in mammals, inactivation of one of the Z chromosomes does not equalise gene expression on the sex chromosomes in birds. Instead, dosage compensation is accomplished in females by increasing transcription of the single active Z chromosome.

Option 4 is the correct answer. 

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