As your text notes, in xx females the dosage of x-linked genes is twice what it is in xy males. however, the level of expression of x-linked genes is about the same in both males and females. in mammals this dosage compensation is the result of x-inactivation in females.a) trueb) false

a) true

Explanation:

It is absolutely right that in mammals dosage compensation occurs due to  X-inactivation in females. It happens because in mammals like humans, females have XX and males have XY as allosomes. Because of the presence of two X chromosomes, each gene is present in 2 copies in females but in males only 1 copy is present as they have only one X chromosome. So in order to compensate for this kind of difference, one of the female X chromosomes undergoes inactivation and this phenomenon is known as dosage compensation.

The X chromosome undergoes inactivation because of its DNA modification and acts very different from other X chromosomes. Several methyl groups are added to the DNA of such X chromosome so as to inactivate it. In general such inactivated X chromosome is known as bar body which appears like a darkly stained structure.

Note: In other lower organisms like drosophila and C. elegans other mechanisms of dosage compensation exist.

In drosophila rather than inactivation of one chromosome in female, the transcription rate of one X chromosome of male is doubled so that it could produce as much transcripts as two X chromosomes of female are producing.

In C. elegans, both the X chromosomes are active but partially. The transcripts produced by two X chromosomes of female equalize the transcripts produced by one X chromosome of hermaphrodite counter part.

B. He was the first to observe live cells in a sample of pond water.

Explanation:

He was a self taught man that created the first microscopes which allowed him and others to see tiny organisms.

The other answers are not correct as Hans made the first microscope, cells existing in liquids were not a critical part of micro biology, and it was Schlieden and Schwann who created the cell theory that stated that all living things were made of cells.