Question

Scientists discover many new species with different mechanisms for dosage compensation between "male" and "female" organisms. Which of the following cases would result in correct sex chromosome dosage between males and females within the species? Choose ALL correct answers 4 points possible A species that has X and Y sex chromosomes where males are XY and females are XX. Gene expression of the SRY gene is doubled in males, and both of the X chromosomes is expressed in females. A species that only has X chromosomes where males are XXX and females are XXXX. Males have 2 Barr bodies and females have 3 Barr bodies. A species that has S and T sex chromosomes where males are ST and females are SS. Gene expression of the single S chromosome in males is doubled and females do not inactivate either S chromosome. A species that has S and T sex chromosomes, where males are TT and females are ST. Females inactivate their T chromosome.

Answer 1

2, 3

Dosage compensation is a process which occurs in organisms to compensate the amount of gene product synthesized by genes located on the sex chromosomes in both males and females.

First option is incorrect because the males need to double the expression of X chromosome not the SRY gene. SRY gene is located on Y chromosome.

Second option is correct because number of bar bodies is equal to the total number of X chromosome minus 1. So, males have three X chromosomes and if they will inactive 2 then only one active X chromosome will be left and females have four X chromosomes and if they will inactive 3 then only one actice X chromosome will be left.

Third option is correct because if males will double the expression of S chromosome, then the amount of gene dosage by S chromosome will be equal in both males and females.

Last option is incorrect because males need to inactivate there one of the T chromosomes.

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