MCAT Biology Question – Sex Chromosomes
- Jan 06, 2017
- MCAT Question of the Day
A. Post-transcriptional modification of half the male sex chromosomes gene products
B. Inactivation of one Z chromosome in males
C. Inactivation of the W chromosome in females
D. Destruction of one Z chromosome in males
Click for Explanation
Opposite to male birds (ZZ), mammalian males (XY) are heterogametic and carry one X and one Y chromosome. Similarly, female birds (ZW) are heterogametic while mammalian females (XX) are homogametic.
In the mammalian XY sex-determination system, females randomly inactivate one of their X chromosomes to prevent a redundancy in gene products (i.e. mRNA and proteins). These inactivated chromosomes are known as Barr bodies.
In the case of bird species, the homogametic males (ZZ) must inactivate one of their Z chromosomes to achieve the appropriate reduction in gene products. Therefore, the correct answer is B.
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